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Effects of iso- and polyvalent substitutions on the short/long-range crystalline order in CuCrO 2 compounds
Abstract
Compounds of pristine CuCrO 2 , doped CuCr 0.96 M 0.03 V 0.01 O 2 (M = Ti, Mn, Ga and Nb), CuCr 0.96 V 0.04 O 2 , CuCr 0.97 Mg 0.03 O 2 , CuCr 0.97 Ni 0.03 O 2 and CuCr 1-x Fe x O 2 (x = 0.03, 0.06, and 0.09) were prepared by conventional solid-state route. Rietveld Refinement method using the Fullprof software confirms the single rhombohedral structure with space group R-3m for all the studied samples. It was found that doped ion having a larger ionic radius shows an increase in the unit cell volume for CuCrO 2 , while the unit cell volume decreases or remains nearly unchanged for dopant having a slightly smaller ionic radius. Negligible strain is observed in the pristine, Mn, Ga and Nb doped samples, whereas other dopants show strained growth. It was found that samples with Ti and Fe doping exhibit the maximum strain. Although, no significant changes in the frequencies of Raman active modes A 1g and E g were detected, strong local distortions were observed in the Mn, Ti and Fe doped samples. In addition, the CuCrO 2 compounds doped with V, Ga, Nb, Ti and Mn ions exhibit splitting of IR active E u and A 2u modes.
... After calcination, the discs were ground and then sintering was carried out twice for 24 h at 1125°C. 32 The thin films of CCO and CCVO were deposited using PLD. A pulsed KrF (wavelength λ = 248 nm) excimer laser was used for ablation repetition at 10 Hz and an energy density of 220 mJ/cm 2 . ...
... The lattice parameters of CCO were a = b = 2.97 Å and c = 17.10 Å. Furthermore at the M site, 4% vanadium was doped resulting in CCVO which has not changed the overall symmetry of the samples having the lattice parameters a = b = 2.97 Å and c = 17.10 Å , as reported elsewhere. 32 The substrate temperature plays a significant role in the crystallinity of the films. Previous reports have shown that with the increase in temperature of the substrate, the crystallinity of CCO is significantly promoted and the structure changes to a more stable phase. ...
... The V and Fe doping contracts the metal oxygen bonds and leads to a depressed p-type conductivity. 32 We have also plotted the temperature versus resistivity graphs that show the high resistivity of the CCVO thin film. It is noted that the electron doping could lead to the partial compensation of holes that might result in an increase in electrical resistivity, as both electrons and holes contribute to the electrical transport, resulting in the decreased electrical resistivity. ...
Delafossite CuCrO2 (CCO), CuCr0.96V0.04O2 (CCVO) thin films were successfully prepared on Si (100) substrates, using the pulsed laser deposition technique. The effect of doping was studied using x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), temperature-dependent resistivity measurements, and I–V characteristics. The XRD results confirmed the single-phase rhombohedral structure of the prepared thin films, and the XAS results conveyed the mixed Cu+ and Cu2+ ions in the CCVO and CCO samples. The valence state of Cr was unaltered under the doping effects and remained + 3 (i.e., Cr+3). The modified hybridization of the O 2p orbitals with the metal d (V, Cr,) orbitals was confirmed in the O K-edge spectra. Insertion of V5+ ions in the CCO lattice introduced an electron doping effect. Thus, the basic p-type character of CCO was affected by the V doping and, therefore, increases in the resistivity or decreases in the p-type character were observed in the I–V measurements. From this study; the method of selective mono-doping can be a useful tool to tailor the bandgap and the type of conductivity in other delafossite semiconductors.
... A. X-ray diffraction studies Figure 1 shows the XRD patterns for doped CuFe 0.96 M 0.03 V 0.01 O 2 (where M = Ti, Ga, and Mn), CuFe 0.96 V 0.01 O 2 , and undoped CuFeO 2 samples. 1% V has been added to the limit phase stabilization at 1273 K. 29 Such a reduction in the phase formation temperature has been reported earlier. 20,29 It is known that the Eu doped samples have impurity phases present beyond 2% doping, 19 Ni doping shows impurity phases at and beyond 2%, 14 and in the case of Mn 5% doping shows impurity phases. ...
... 1% V has been added to the limit phase stabilization at 1273 K. 29 Such a reduction in the phase formation temperature has been reported earlier. 20,29 It is known that the Eu doped samples have impurity phases present beyond 2% doping, 19 Ni doping shows impurity phases at and beyond 2%, 14 and in the case of Mn 5% doping shows impurity phases. 15 All the synthesized samples exhibited a single delafossite phase, confirming the rhombohedra structure having space group R-3m (space group No. 166), and no impurity peaks were detected for the samples within the experimental limits. ...
... 15 All the synthesized samples exhibited a single delafossite phase, confirming the rhombohedra structure having space group R-3m (space group No. 166), and no impurity peaks were detected for the samples within the experimental limits. [14][15][16][17][18][19][20][21][22][23][24][25][26][27]29 The Rietveld refinement method was used for refining the structural and cell parameters using Fullprof software. 30 One such refined XRD pattern of reference composition CuFe 0.96 Ti 0.03 V 0.01 O 2 (CFTiV) sample is presented in Fig. 2. The value of lattice constants, reliability factors including other crystallographic data are given in Table I. ...
Single phase CuFeO2, CuFe0.96M0.03V0.01O2 (M = Ti, Mn, and Ga), and CuFe0.96V0.04O2 compounds with space group R3¯m were prepared through a newly developed solid-state technique using annealing under high vacuum. Raman studies demonstrate, for the first time, a minor shift in Ti and Mn-doped samples as well as the Jahn–Teller effect induced distortions around 500 cm⁻¹ along with well-documented peaks of Eg and A1g modes. Mössbauer studies confirm the presence of iron in high spin Fe³⁺ and quadruple splitting values endorsing the presence of octahedron distortions. An increase in the electrical conductivity at low temperatures is observed due to the enhanced charge doping with minor variations related to local distortions. Low-temperature magnetic studies of pristine and Ti-doped samples demonstrate paramagnetic nature up to 25 K. However, on one hand, the pristine sample shows a sharp rise in magnetization values at low applied fields and on the other side, Ti-doped samples exhibit nearly linear behavior. Dielectric measurements confirm weakening of electrical ordering near the magnetic transition in distorted Ti-doped samples, compared to pure CuFeO2 sample. Level of charges along with its local distortions affected mobility has significant effects on transport and multiferroic nature of these samples.
... The crystallite size was determined using the following Eq. (2) [18][19][20]: ...
A red emitting luminescent novel double perovskites magnesium tungstate (Mg3WO6) activated with Eu³⁺ were prepared and characterized for structural and photoluminescence (PL) properties. The phosphors were prepared using the standard solid-state reaction (SSR) method, with varying Eu³⁺ concentrations ranging from 1 mol% to 4 mol%. All the phosphor under study were thoroughly examined by utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDAX) analysis for structural and morphological aspects. The Rietveld refinement matching of powder XRD patters confirms the Monoclinic crystalline structure of the phosphor under study. Moreover, the crystallite size is computed using Debye-Scherrer (D-S) formulation. The monoclinic crystallized Mg3WO6:Eu³⁺ phosphors show agglomerated surface looking like a cluster of particles, which primarily due to the high-temperature calcination. When excited at 278 nm, 396 nm, and 536 nm excitations, the phosphor series doped with Eu³⁺ exhibited standard PL emission of activator ions. Under all three applied excitations, the phosphors displayed red spectral emission with notably high luminescence intensity for which ⁵D0-⁷FJ (J = 1 and 2) standard transition of Eu³⁺ ions are responsible. The effect of doping and concentration quenching were investigated and discussed. The decay kinetics of the phosphors were examined using PL decay lifetime measurements for λex = 396 nm and λem = 616 nm, and corresponding lifetime was determined. Additionally, the PL quantum efficiency, a key parameter for evaluating the potential of the phosphors, was calculated based on the measured PL decay time using Auzel’s model. The CIE color coordinates significantly falling within red region of the CIE diagram, confirming standard color emission and related photometric parameters were determined. As a result, the synthesized phosphor series under investigation found capable in their application in light illumination devices.
... Meanwhile, new absorption functional groups appear on the Al2O3/CuCrO2/AC electrode which indicates the formation of CuCrO2 [36]. Whereas the appearance of spinel phase also exhibits at wavenumber 726.67 cm -1 which relates to the vibration of Cr -O in the octahedrans of the spinel phase [37], [38]. Vibration peak located at wavenumber 642 cm -1 can be ascribed to the stretching vibration of the Cu-O bond [39]. ...
The development of the supercapbattery has become the focus of energy storage research due to their potential to increase energy and power density. This research is focused on developing a modification of silicon (Si) porous as an anode with Al2O3/CuCrO2/AC composite as a cathode of supercapacitor. These electrodes were synthesized using LA133 binder with deionized water as solvent. The supercapacitor electrode uses an aluminum foil substrate, while the Si electrode uses a cupper foil substrate. The structural and morphological characterization of the electrodes were identified through XRD, FTIR, and SEM tests, while the electrochemical performance characterization using Galvanostatic Charge-Discharge (GCD) instruments. The results of XRD data analysis of thin film electrodes of supercapacitor showed diffraction peaks which indicated the phases Al2O3/CuCrO2/AC and Si porous. The absorption functional groups of Al2O3/CuCrO2/AC and Si porous were identified through FTIR characterization. The results of SEM showed the addition of CuCrO2 and structure modification of silicon into porous caused increasing value of porosity. The electrochemical performance of the optimum point at Al2O3/CuCrO2/AC condition, showing a specific capacitance of 50.3 F/g, an energy density of 36.499 Wh/kg, and a power density of 433.6 W/kg. The combination of Al2O3/CuCrO2/AC//Si Porous 16 for supercapbattery devices shows performance with a specific capacitance of 14.4 F/g, an energy density of 6.1 Wh/kg, and a power density of 33.6 W/kg. These results indicate an increase in electrochemical performance compared with Si anodes without modification.
... Among Cu delafossites, the copper chromium oxide (CuCrO 2 ) is considered the most promising, as it presents a favourable covalent mixing between Cr 3? and O 2-, a high density of Cr 3d states near the VBM and a high band gap. Additionally, its optoelectrical properties are easy tuneable as the structure allows facile substitution with aliovalent and/or isovalent cations at the Cr site [81,82,151,152]. Finally, it has a low synthesis temperature and a favourable thermal stability in air. ...
Transparent conductive oxides (TCOs) constitute a class of materials that combine high electrical conductivity and optical transparency. These features led to the development of the transparent electronics applications, such as flat panel displays, “smart” windows or functional glasses. N -type TCOs dominate the applications market, and the lack of a suitable p-type counterpart limits the fabrication of a completely transparent active device, which might be considered as a technological breakthrough. Among the wide range of p-type candidates, delafossite CuCrO 2 (and its out-of-stoichiometry derivatives) is a promising material to achieve the desired p-type TCO properties as, up to date, it is presenting the foremost trade-off between optical and electrical properties. The present paper covers the research work and the major achievements related to copper chromium delafossite. A comprehensive overview of fabrication methods and opto-electronic properties is presented. The source of doping and the charge carriers transport mechanism are also thoroughly discussed.
Graphical abstract
... For all samples in Fig. 5(a), three Raman-active peaks were observed at approximately 203, 450, and 699 cm À1 , corresponding to A g , E g , and A 1g , respectively [17,37,38]. Furthermore, a broad band centered around 540 cm À1 is due to the presence of local distortions [39]. This band corresponds to the existence of copper vacancies (V Cu ) in the delafossite structures, which is attributed to the native intrinsic acceptor defects [38,40]. ...
The thermoelectric performance of CuCr1-xMgxO2 materials in terms of multi-scale defects induced at various Mg dopant concentrations (x = 0–0.3) was thoroughly studied in this paper. At 748 K and for x = 0.05, 0.15, and 0.30, we report the following power factors and thermal conductivities: 175, 213, and 2.3 μW/m K² and 7.85, 5.60, and 3.82 W/m K, respectively. In the low doping regime (x < 0.15), the thermoelectric performance is mainly dependent on hole carriers originated from point defects via Mg substitution on Cr sites, whereas the thermoelectric properties reduce significantly for x ≥ 0.15 due to nanoscale secondary phases (MgCr2O4, Cu2O and CuO) and mesoscale grain boundaries. At 748 K, our CuCr0.85Mg0.15O2 samples exhibit a high figure of merit ZT = 0.028, which is better than those of other CuCr1-xMgxO2 and related delafossite materials. The correlations between the structural and thermoelectric properties of CuCr1-xMgxO2 materials are also discussed in detail.
A set of Sm3+ doped calcium tungstate double perovskite (Ca3WO6) samples was synthesized via a combustion synthesis to explore their luminescence properties. The X-ray diffraction (XRD) study revealed the formation of monoclinic crystal structure of the phosphor. Surface morphology was investigated using scanning electron microscopy (SEM), wherein, the probable cathodoluminescence was observed with agglomeration. In examine the elemental distribution, the phosphor under study was characterized via the energy-dispersive X-ray analysis (EDAX) analysis, confirm even distribution of constituent elements. Moreover, to examine the mode of vibrations corresponds to available functional group, FTIR study is carried out. When exciting the phosphors with NUV and blue light at 278 and 410 nm, the phosphors exhibited a strong orange-red photoluminescence (PL) emission peaking at 567, 605 and 650 nm. These emissions are attributed to Sm3+ characteristic transition occurring from 4G5/2-6H5/2,6H7/2 and 6H9/2, respectively. The PL intensity was found maximum at a 2% concentration of Sm3+, with subsequent quenching attributed to multipolar interaction, to be precise dipole-dipole interaction. The temperature-dependent PL (TDPL) measurements showed a reduction in intensity with increasing temperature. The intensity of PL emission maintained 74.2% at 150 C°, indicating high thermal stability with an activation energy of 0.184 eV. Moreover, the CIE chromaticity coordinates confirmed pure orange-red emission. By means of CIE, color corelated temperature (CCT) is computed and discussed. Overall, the intense orange-red PL emission under 278 nm and 410 nm excitation suggest that the phosphor under study has potential to use in display materials and in illuminating device applications.
A series of tungstate double perovskite Ca3 WO6 doped with Tb3+ was prepared by a combustion process using urea as a flux. The crystal structure identification of Ca3 WO6 :Tb3+ phosphors was done using X-ray diffraction patterns, and a monoclinic structure was discovered. The Fourier transform infrared spectrum of Ca3 WO6 :Tb3+ displayed characteristic vibrations of tungstate bonds. Under 278 nm excitation, Ca3 WO6 :Tb3+ exhibited intense downconversion green emission, which corresponded to the 5 D4 -7 FJ (J = 4,5) transitions of Tb3+ . The phosphor exhibited the highest photoluminescence (PL) intensity when it was doped with 1 mol% of Tb3+ ; later intensity quenching appeared to be due to the multipolar interaction at higher dopant concentrations. Moreover, high-quality thermoluminescence (TL) was detected when phosphors were irradiated using beta rays. The effects of Tb3+ concentration and beta dose on TL intensity were the two major aspects studied in detail. The TL intensity demonstrated excellent linear response to the applied range of beta dose. The trap parameters of the studied phosphors were computed by the peak shape approach and glow curve deconvolution. The fading effect on TL intensity was studied by recording the TL glow curves after 1 month of beta irradiation. Obtained results from the PL and TL characterizations showed that the phosphors under study have the potential to be used in lighting displays and in thermoluminescence dosimetry.
The breakthrough of transparent electronics is hindered by the lack of p-type semiconducting oxides with adequate optical transparency and electrical conductivity, limiting the conception of see-through optoelectronic devices as well as transparent photovoltaic devices. In this framework, copper chromium oxide (CuCrO2) arises as promising candidate thanks to its optical, electrical and manufacturing properties. Moreover, it is well known that the composition of the film plays a major role in its properties, and that defects generated by the out of stoichiometry can act as dopants. This work was focused on the synthesis of out of stoichiometry CuCrO2 thin films by atmospheric pressure CVD and their integration into see-through optoelectronic devices. The effect of the deposition temperature was investigated to maximize the electrical conductivity and the transparency of the thin films. The stoichiometry of CuCrO2 films was tuned to further enhance the optoelectronic properties of the material. As highlighted result, we report the synthesis of single phase Cu-rich CuCrO2, characterized by low resistivity, around 0.1 Ω.cm, and wide energy gap of 3.15 eV. The synthesis of an oxygen-poor environment has been demonstrated to impede the formation of CuO, detrimental to the properties of the films. This allows the deposition of films composed of Cu2O and CuCrO2. These nanocomposite films are characterized by carrier mobility of 0.65 cm² V-1 s-1, higher than for the Cu-rich CuCrO2 films, resulting in the lowest resistivity value of 0.02 Ω.cm of this study.Out of stoichiometry CuCrO2 thin films have been successfully integrated as hole transport layer (HTL) in PBDD4T-2F:PC70BM Organic Solar Cells with architecture glass/ITO(anode)/HTL (PEDOT:PSS or CuCrO2.)/ Organic active layer/ETL (LiF)/cathode (Al). The effect of the stoichiometry of the CuCrO2 films, varied between 40% and 100%, on the Power Conversion Efficiency (PCE) was studied. We obtain an increasing PCE for Cu-rich CuCrO2 as HTL. The optimal cationic ratio was achieved for Cu/(Cu+Cr)= 65%, due to the best trade-off between optical and electrical properties, with a corresponding PCE of 3.1%. The stability of these devices in atmospheric conditions was studied and compared to the one of PEDOT:PSS based-OSC. The integration of oxides as HTL improved the stability in atmospheric conditions of the device, with a lifetime for oxides-based solar cells double when compared to polymer-based photovoltaic devices.The reusability of the functionalized substrates, glass/ITO/CuCrO2, was tested by the elimination of the top stack Aluminum/ETL/Active layer through a simple chemical method. This was followed by the assembly of new cells above the substrate/ITO/ CuCrO2. The properties of the HTL as well as the performances of the devices based on the recycled HTL were unaltered. This will help the development of new performant and sustainable organic photovoltaic devices.Additionally, out of stoichiometry CuCrO2 thin films were implemented in combination with ZnO in a fully oxides-based transparent planar p-n junction. This transparent diode was entirely synthesized by chemical deposition techniques at low temperature and atmospheric pressure, with no required post-deposition treatment. The device architecture was optimized through the tuning of deposition parameters for the p and the n-type oxides. The optimized diode, corresponding to a nanocomposite Cu2O+CuCrO2 coupled with polycrystalline ZnO, shows an extremely high rectifying behaviour, Ion/Ioff (±2.5V) around 100000, the highest ever reported, with a transmittance in the visible around 75%. The fitting of the diode characteristic led to a turn-on voltage of 1.3 V, an ideality factor of 3.15, a shunt resistance of 640 kohm.cm-2, and a series resistance of 340 kohm.cm-2. The extremely high performances and the manufacturing advantages of these devices are extremely appealing for the transparent electronic industry.
Electrochemical removal of nitrogen oxides (NOx) by solid electrolyte cells (SECs) is a promising technology due to no required reductant. Herein, a series of La0.8Sr0.2Mn1−xNixO3 (0 ≤ x ≤ 0.5) perovskites were first synthesized and utilized as the electrode materials of SECs. The role of Ni substitution in electrode performance and NOx reduction mechanism were revealed by various experimental characterization and first-principle calculations. The results indicate that the moderate Ni substitution (x ≤ 0.3) increased the NOx conversion of electrodes while reduced the polarization resistance. The further investigation shows that this improvement was attributed to the more surface oxygen vacancies, better reducibility and higher Mn⁴⁺ proportion of the Ni-substituted perovskites. The electrochemical impedance spectroscopy (EIS) shows that these changes facilitated the NOx adsorption and dissociation processes on the electrode. According to first-principle calculations, the Ni-substituted perovskite had a lower formation energy of surface oxygen vacancy, while the NO molecule adsorbed on defect surface gained more electrons thus was easier to be reduced and dissociated. Finally, the electrode performance at different operating temperatures and the operational stability were verified.
Introduction: Harvesting the waste heat emitted from the activities of humanity based on thermoelectric devices is an appropriate way to reduce the overconsumption of fossil fuel nowadays. Methods: In this work, CuCr0:85Mg0:15O2 compounds prepared by conventional solid-state reaction method were investigated to find out that the short sintering time is enough for thermoelectric applications, directly low the cost of the devices. Results and Conclusion: We find out that there is a significant change in the crystal structure, the chemical state, and thermoelectric properties along with the increase of the sintering time, but eventually, the dimensionless figure of merit ZT is almost constant regardless of the long or short sintering time which means that the increase of electrical conductivity will compromise the increase of thermal conductivity. The highest ZT value is 0.03 measured at 500 oC for both samples prepared at the sintering time of 3 and 12 hours.
Herein, delafossite CuCrO 2 nanoparticles were synthesized through a polymeric citrate precursor method, followed by heating at 900 C in air. The BET surface area of the CuCrO 2 nanoparticles was found to be 235 m 2 g À1 , which was more than 500 times that of bulk CuCrO 2 (0.47 m 2 g À1) and 2–4 times that of the reported CuCrO 2 nanoparticles (50–100 m 2 g À1) (Y.-T. Nien et al., Mater. Chem. Phys., 2016, 179, 182– 188 and D. Xiong et al., J. Mater. Chem., 2012, 22, 24760–24768). In the photoluminescence spectra of the CuCrO 2 nanoparticles, a strong luminescent emission peak was observed at $460 nm in the blue light region. The resulting transmittance value of the CuCrO 2 nanoparticles was found to be 77% in the visible region, and the direct band gap energy was determined to be 3.09 eV via UV-vis spectroscopy. The dielectric properties as a function of frequency and temperature and photocatalytic degradation of the organic pollutants in an aqueous solution were also investigated. CuCrO 2 nanoparticles also showed remarkable enhancement in the catalytic degradation of methylene blue in H 2 O under sunlight irradiation. The plausible fragmentation and the structural changes in the methylene blue molecule were further demonstrated via mass spectrometry.
To stabilise ferroelectric-tetragonal phase of BaTiO3, the double-doping of Bi and Mn up to 0.5 mol% was studied. Upon increasing the Bi content in BaTiO3:Mn:Bi, the tetragonal crystal-lattice-constants a and c shrank and elongated, respectively, resulting in an enhancement of tetragonal anisotropy, and the temperature-range of the ferroelectric tetragonal phase expanded. X-ray absorption fine structure measurements confirmed that Bi and Mn were located at the A(Ba)-site and B(Ti)-site, respectively, and Bi was markedly displaced from the centrosymmetric position in the BiO12 cluster. This A-site substitution of Bi also caused fluctuations of B-site atoms. Magnetic susceptibility measurements revealed a change in the Mn valence from +4 to +3 upon addition of the same molar amount of Bi as Mn, probably resulting from a compensating behaviour of the Mn at Ti4+ sites for donor doping of Bi3+ into the Ba2+ site. Because addition of La3+ instead of Bi3+ showed neither the enhancement of the tetragonal anisotropy nor the stabilisation of the tetragonal phase, these phenomena in BaTiO3:Mn:Bi were not caused by the Jahn-Teller effect of Mn3+ in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi3+.
The p-type semiconductor Cu(I)-based delafossite transparent conducting oxides are good candidates to be used as hole collectors in dye-sensitized solar cells. The Al-doped CuGaO2 has been synthesized by hydrothermal method and its properties have been investigated as cathode elements in ruthenium dye N719-sensitized solar cells. The photocurrent density (Jsc) and the open-circuit voltage (Voc) for 5% Al-doped CuGaO2 microparticles using N719 dye were approximately two times higher than undoped CuGaO2 microparticles. The integration of aluminum dopants in the delafossite structure improves the photovoltaic performance of CuGaO2 thin films, due to the excellent optical transparency of CuGaO2 in the visible range as well as the improved electrical conductivity caused by the apparition of the intrinsic acceptor defect associate (AlCu••2Oi″)″ with tetrahedrally coordinated Al on the Cu-site.
A series of Cu(Cr1−xFex)O2 and Cu(Cr1−yMgy)O2 (0.0 ≤ x,y ≤ 0.05) nanocrystalline samples with high surface area were prepared using hydrothermal synthesis. The effect of Fe3+ substitution for Cr3+ on the structural, morphological, optical and electrical characteristics of CuCrO2 nanoparticles was investigated in comparison with Mg-doped samples. X-ray diffraction study showed that the solubility limit was around 3 at% for both dopants and beyond this concentration the formation of spinel phases was observed. The incorporation of the tri- and divalent dopants induced a slight expansion in a- and c-parameters. Transmission electron microscopy examination indicated that the average crystallite size (12 nm for undoped) decreased with increasing doping amount of up to x = 0.03 (8.5 nm) and y = 0.05 (7 nm). Moreover, the introduction of Fe and Mg led to an increase in the size distribution of the crystallites. All samples exhibited transmittance above 80 % at 700 nm wavelength and transmittance was enhanced for all doping concentrations except for x = 0.05. A similar trend was also observed for the direct band gaps, where only 5 at% Fe doping induced a red-shift of Eg. The direct band gaps were estimated to be 3.09 eV for x = 0.03 and 3.07 eV for y = 0.03. At room temperature, the minimum achieved electrical resistivity was measured to be 6.4 and 0.068 kΩ cm for the samples with x,y = 0.03, respectively. These values are lower by a factor of ~2 and 166 than that of the undoped CuCrO2 sample (11.8 kΩ cm). All samples behaved like semiconductors, and the thermally activated energy for Cu(Cr0.97Mg0.03)O2 and Cu(Cr0.97Fe0.03)O2 pellets were found to be 45.40 and 92.5 meV, respectively.
P-type transparent conducting thin films of copper aluminium oxide were prepared by DC sputtering of polycrystalline
CuAlO target, which was fabricated by heating a stoichiometric 2 mixture of Cu2O and Al2O3 at 1375 K for 24 h. Thin films of
CuAlO2 were deposited on Si (4 0 0) and glass substrates. The sputtering was performed in ArqO2 (40 vol.%) atmosphere and
the substrate temperature was 453 K. X-ray diffraction spectra of the films showed the peaks that could be assigned with those
of the crystalline CuAlO2. Fourier transform infrared spectra showed Cu–O, Al–O, O–Cu–O bonding. UV–Vis–NIR spectrophotometric
measurement showed high transparency of the films in the visible region. Both direct and indirect band gaps were found
to exist and their corresponding estimated values were 3.66 and 2.1 eV, respectively. The room temperature conductivity of the
film was fairly high and was of the order of 0.08 S cmy1, while the activation energy was ;0.26 eV. Thermoelectric power
measurement indicated positive value of Seebeck coefficient and its room temperature value was q128 mV Ky1. Positive value
of Hall coefficient (R sq16.7 cm3 Cy1) also confirmed p-type conductivity of the films.
H
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This work describes the scandium doping effect on the structural and magnetic properties of delafossite-type oxides CuCr1−xScxO2. The lattice parameters were found to vary according to Vegard’s low. A reflection broadening is observed, that is ascribed to local lattice distortion due to the ionic radius difference between Cr 3+ and the non-magnetic dopants. Magnetic susceptibility measurements show that the dominant interactions are antiferromagnetic (AFM) but that doping induces significant changes. The coupling between the local spins at the Cr sites and doped metal transition may enhance spin fluctuations at the Cr sites, which break the residual magnetic degeneracy as fluctuation-induced symmetry breaking in a highly magnetic degenerate ground state manifold of some frustrated systems.
The CuCo0.5Ti0.5O2, CuNi0.5Ti0.5O2 and CuNi0.5Sn0.5O2 quaternary oxides have been prepared using direct solid state reaction. AgNi0.5Ti0.5O2 and CuScO2 have been obtained only by exchange reaction.
They exhibit a 3R-delafossite type structure. For CuCo0.5Ti0.5O2, a 2H-polytype is also observed.
The lattice constant variation with the size of the cation occupying the B-site is similar for both mixed (AB0.5′B0.5″O2) and simple ABO2 delafossites. The evolution with the size of B-site cations of the BO6 or (B′, B″)O6 octahedron D3d-deformation is explained by that of the covalency of the σ(B-O) bonds. No evidence of a ordering has been detected in the materials.
The electronic structure of the p-type transparent conducting oxide CuCrO{sub 2} has been studied by x-ray photoemission, x-ray absorption, and x-ray emission spectroscopies. The upper part of the valence band derives mainly from Cu?3d and Cr?3d states while the lower valence-band states are of dominant O?2p atomic character, but with pronounced mutual hybridization among Cu?3d, Cr?3d, and O?2p states. Site specific electronic excitations have been studied by resonant inelastic x-ray scattering at the Cu?L and Cr?L edges. Inelastic loss at the Cu?L edge is dominated by on-site interband excitations similar to those found in Cu{sub 2}O, while at the Cr?L edge localized excitations arising from ligand field splitting of the Cr?3d levels are observed. Mg doping on the Cr sites in CuCrO{sub 2} is shown to lead to a pronounced shift in the Fermi level toward the edge of the valence band. The experimental data are compared to electronic structure calculations on CuCrO{sub 2} carried out using density-functional methods corrected for onsite Coulomb repulsion.
In this study, we present a facile hydrothermal synthesis of ultrasmall delafossite CuCrO2 nanocrystals, with a typical size of 15 nm × 5 nm, and a high surface area of 87.86 m2 g−1, thermally stable up to 400 °C. The screen-printed CuCrO2 films sintered at different temperatures and under different atmospheres present different optical transmittances, tunable BET surface areas, dye adsorbing amounts, and tunable hole transport rates and hole recombination kinetics, which allows the optimization of the performance of p-type dye sensitized solar cells (DSSCs) based on CuCrO2 photocathodes. At optimized conditions, an open circuit voltage of 102 mV, a short circuit density of 0.491 mA cm−2, a fill factor of 0.398 and an overall photoconversion efficiency of 0.0194% were finally achieved for a coumarin 343 dye sensitized CuCrO2 solar cell. This record is acceptably high in comparison to a DSSC based on an NiO photocathode prepared and tested in similar experimental conditions. The light harvesting properties, charge collection capability, and flat-band potential of CuCrO2 photocathodes and the NiO photocathode have been critically compared.
Delafossite p-type CuFeO 2 (CFO) semiconductors were synthesized by a modified solid state reaction technique and investigated by x-ray diffraction, x-ray photoemission spectroscopy (XPS), energy dispersive x-ray spectroscopy, and scanning electron microscopy, revealing the single-phase nature of CFO with 1:1 Cu/Fe atomic ratio. The valance states of CFO were examined by XPS and suggest Cu and Fe ions are in +1 and +3 valance states with high spin S =5/2 . The “turn-on field” which is the macroscopic field needed to get an emission current of 9 nA, was calculated as 5.72 V /μ m . Room temperature Raman spectra of CFO displayed two main Raman active modes at E g ∼351 cm -1 and A g ∼692 cm -1 in accord with other delafossite structures. Temperature dependent Raman spectra showed that both the modes shifted to lower frequency with significant decrease in intensity with increase in temperature. Frequency shift and linewidth of both phonon lines matched well with the theoretical damped harmonic oscillator model based on thermal expansion of the lattice and their anharmonicity coupling with other phonons.
The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
Ultrasonic velocity measurements on the magnetoelectric multiferroic compound CuFeO(2) reveal that the antiferromagnetic transition observed at T(N1) = 14 K might be induced by an R3m --> pseudoproper ferroelastic transition. In that case, the group theory states that the order parameter associated with the structural transition must belong to a two-dimensional irreducible representation E(g) (x(2) - y(2), xy). Since this type of transition can be driven by a Raman E(g) mode, we performed Raman scattering measurements on CuFeO(2) between 5 and 290 K. Considering that the isostructural multiferroic compound CuCrO(2) might show similar structural deformations at the antiferromagnetic transition T(N1) = 24.3 K, Raman measurements have also been performed for comparison. At ambient temperature, the Raman modes in CuFeO(2) are observed at ω(E(g)) = 352 cm(-1) and ω(A(1g)) = 692 cm(-1), while these modes are detected at ω(E(g)) = 457 cm(-1) and ω(A(1g)) = 709 cm(-1) in CuCrO(2). The analysis of the temperature dependence of the modes in both compounds shows that the frequencies of all modes increase with decreasing temperature. This typical behavior is attributed to anharmonic phonon-phonon interactions. These results clearly indicate that none of the Raman active modes observed in CuFeO(2) and CuCrO(2) drive the pseudoproper ferroelastic transitions observed at the Néel temperature T(N1). Finally, a broad band at about 550 cm(-1) observed in the magnetoelectric phase of CuCrO(2) below T(N2) could be associated with magnons.
Red beryl from Utah is chemically homogeneous and contains only Fe < 0.163, Mn < 0.018, and Mg < 0.016 apfu. Channel sites contain only up to Cs 0.011, K 0.009, Rb 0.004, and Na 0.004 apfu. This suggests only very slight tetrahedral (Cs,K,Rb)Li□-1Be-1 substitution, octahedral Na(Fe²⁺,Mg)□-1Al-1 substitution can be excluded. Fe and Mn are trivalent as documented by Mössbauer spectroscopy and optical absorption spectroscopy. Red beryl optimized formula is ∼[(Cs,Rb,K)0.02□0.98]Σ1.00□1.00(Al1.79Fe³⁺0.16Mn³⁺0.02Ti⁴⁺0.02Mg0.01)Σ2.00Be3(Si6O18). Location of Mn³⁺ was estimated to the octahedral Al³⁺ site, other choices are improbable due to the bond-length requirements. No Mn³⁺-induced Jahn-Teller structural distortion was detected due to site symmetry restrictions and small Mn³⁺ content. However, optical spectroscopy shows broad band at ∼7190 cm⁻¹ assigned to the excited level of the spin-allowed pseudo-tetragonal split E ground state of elongated six-fold Mn³⁺ coordination. Crystal field calculations indicate that the local Mn³⁺ environment complies well with crystal chemical expectations for Jahn-Teller distorted Mn³⁺O6 octahedra.
The effect of 1 and 2 mol % V addition on sintering conditions, structural and functional properties of NbLi co-doped PZT ceramics, prepared by conventional ceramic method, was systematically studied, by different experimental techniques. The reported results show that the increasing amount of vanadium, as a substitute for niobium, decreases the optimal sintering temperature with 100–150 °C, but slightly reduces the piezoelectric, ferroelectric, and electromechanical properties of these ceramics. In addition, the presence of vanadium increases the lattice tetragonality and grain size, promoting a harder piezoelectric behaviour, mostly in the absence of niobium. EPR spectra exhibit well-defined hyperfine splitting characteristics for V4+ state, dispersed in the lattice as VO2+ ion. Additionally, complex paramagnetic defects (charged oxygen vacancies and associated defects) are evidenced for 2 mol % vanadium addition. The results were explained by assuming that vanadium promotes the B-site Li substitution, compensated by oxygen vacancies, while niobium facilitates the A-site Li substitution with lead vacancies formation and partial reduction of V5+ to V4+. Thus, indirect information about lithium location is provided.
Raman scattering and infrared reflectance spectra of CuCrMgO films (\emph{x}=0.03, 0.06 and 0.09) in the temperature range of 5-300 K have been studied combining with the first-principles calculation. The abnormal redshift of Raman mode center with decreasing the temperature below 100 K for lightly doped film (\emph{x}=0.03) is ascribed to the Cr 3\emph{d}-O 2\emph{p}-Cu 3\emph{d} interaction. Strong disturbance of the local spin fluctuation at Cr sites from heavily Mg doping films (\emph{x}=0.06 and 0.09) drives the mode center into normal blueshift with decreasing the temperature. With further decreasing the temperature, the out-of-plane structure increases the internal spin-charge coupling. It enhances the spin-flip splitting and brings back the abnormal redshift of the Raman mode center. Similar but more obvious trend can be found from temperature-dependent infrared mode center shifts. Two successive magnetic transitions were observed at corresponding N\'{e}el temperature T around 24.7 K and T around 23.0 K, as manifested by magnetoresistance measurements. The interesting phenomena of phonon dynamics are suggested to be manipulated by the spin structures during magnetic transitions.
Delafossite CuCr1-xFexO2 (0.0 ≤ x ≤ 0.15) semiconductors were synthesized using a self-combustion urea nitrate process. The effects of Fe concentration on its microstructural, optical, magnetic, and electrical properties were investigated. X-ray diffraction (XRD) analysis results revealed the delafossite structure in all the samples. The lattice spacing of CuCr1-xFexO2 slightly increased with increasing substitution of Fe at the Cr sites. The optical properties measured at room temperature using UV-visible spectroscopy showed a weak absorbability in the visible light and near IR regions. The corresponding direct optical band gap was about 3.61 eV, exhibiting transparency in the visible region. The magnetic hysteresis loop measurements showed that the Fe-doped CuCrO2 samples exhibited ferromagnetic behavior at room temperature. This indicated that the substitution of Fe3+ for Cr3+ produced a mixed effect on the magnetic properties of CuCrO2 delafossite oxide. The temperature dependent resistivity measurements clearly revealed the presence of superconductivity in the CuCr1-xFexO2 with a superconducting transition up to 118 K.
Structural stability of a multiferroic compound CuFeO2 belonging to the delafossite family has been investigated at high pressures using in-situ Raman spectroscopy. At ambient conditions, CuFeO2 has a rhombohedral structure with space group R3¯m. It has two Raman active modes, identified as Eg and A1g. Both Raman mode frequencies harden with pressure. At 18GPa, the doubly degenerate mode Eg splits, followed by softening of one of the split components. This is also accompanied by rapid softening of the high frequency mode. Features observed across 18GPa confirm the reported structural phase transition. Beyond 23GPa, there is an abrupt loss of Raman intensity and no Raman spectra could be recorded. This could be due to another structural transition. Raman spectroscopic data in the first high pressure phase give evidence for rearrangement in the FeO6 octahedra which eventually leads to an increased coordination of copper in the second high pressure phase. Using the temperature dependence and the present pressure dependence of Raman mode frequencies of CuFeO2, implicit and explicit contributions to their anharmonicity in the ambient phase are separated. The Raman spectroscopic data are correlated with available structural data for the delafossite family of compounds.
RuO2 nanoparticles (RuO2 NPs) have been successfully synthesized by the hydrothermal method. Structure and the particle size have been determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). UV-Vis spectra reveal that the optical band gap of RuO2 nanoparticles is red shifted from 3.95 to 3.55eV. BET measurements show a high specific surface area (SSA) of 118-133m(2)/g and pore diameter (10-25nm) has been estimated by Barret-Joyner-Halenda (BJH) method. The crystallite size and lattice strain in the samples have been investigated by Williamson-Hall (W-H) analysis assuming uniform deformation, deformation stress and deformation energy density, and the size-strain plot method. All other relevant physical parameters including stress, strain and energy density have been calculated. The average crystallite size and the lattice strain evaluated from XRD measurements are in good agreement with the results of TEM.
Copyright © 2015 Elsevier B.V. All rights reserved.
We investigated in this paper a new mixture +3/+2 B cations delafossites by the doping at Cr3+ sites in CuCrO2 by nonmagnetic cation Ti2+. Ceramics of CuCr1-xTixO2 (0 <= x <= 0.1) were prepared via solid state synthesis techniques in a controlled atmosphere of O-2. The compound crystallized into the 3R delafossite phase with hexagonal structure. The slightly different size in B cations induced a slightly variation in unit cell parameters. We modulate the spin chirality by the effect of spin dilution for Ti2+ on the structural and magnetic properties of delafossite CuCrO2 having a S = 3/2 antiferromagnetic triangular lattice (ATL).
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The structure, Raman spectroscopy, magnetization, and dielectric properties of delafossite-type oxide CuCr1−xAlxO2 have been characterized. It was found that Al substitution generates an anisotropic effect on the structure, besides magnetic dilution. The temperature dependence of all samples exhibits paramagnetic behavior at high temperature. Above x=0.2 the ferromagnetic transition at 120K disappears. It is argued that Al substitution destabilizes the antiferromagnetic order of Cr3+ ions and modulates the spin configuration, leading to a weak ferromagnetism. The coupling between the magnetic order and ferroelectric order is also characterized.
We present an experimental and theoretical study on the structural properties of ZnO nanoparticles embedded in silica. The ZnO–SiO2 nanocomposite was prepared by ion implanting a Zn+ beam in a silica slide and by annealing in oxidizing atmosphere at 800°C. From an experimental point of view, the structural properties of the ZnO–SiO2 nanocomposite were studied by using glancing incidence X-ray diffraction. According to the results, zinc crystalline nanoclusters with an average diameter of 13nm are in the as-implanted sample. The annealing in oxidizing atmosphere promotes the total oxidation of the Zn nanoclusters and increases their size until to an average of 22nm. Moreover, the formed ZnO nanocrystals have a preferential (002) crystallographic orientation. From a theoretical point of view, the preferential orientation of the ZnO nanoparticles can be explained satisfactory by the minimization of the strain energy of the nanoparticles placed in proximity of the surface of the matrix.
In this paper we investigate the vibrational properties of CuGaO2 delafossite by means of Raman experiments and ab initio calculations. Both investigations have been performed at ambient pressure and also at high pressure. The two Raman-active modes have frequencies wEg=368±1cm-1 and wA1g=729±1cm-1 , and pressure coefficients 2.78±0.03cm-1/GPa (Eg) and 4.64±0.09cm-1/GPa (A1g) . Raman experiments indicate the existence of a phase transition beginning at 26±1GPa . At about the same pressure, ab initio calculations show the presence of a dynamical instability, possibly related to the phase transition. The phonon dispersion curves are also discussed.
We investigated the structural, magnetic, transport, and thermoelectric properties of polycrystalline delafossite oxides, CuCr1−xMgxO2 (0⩽x⩽0.04). We found that, with the substitution of Mg2+ ions at the Cr site, the resistivity and Seebeck coefficient drastically decrease without a change of Néel temperature (TN=26 K). In contrast to the x-independent TN, the deduced Curie-Weiss temperature linearly varies from −170 to −100 K with the increase of x. A crossover occurs in the conductivity from a thermal activation behavior to variable range-hopping one at Tcross, around which the temperature dependence of magnetization starts to deviate from the Curie-Weiss form. Furthermore, the negative magnetoresistance effect for CuCr0.96Mg0.04O2 compound is observed only in the variable range-hopping regime and is enhanced around TN. These results clearly indicate the coupling between the doped hole and the local spin at the Cr site.
Although the pure delafossite CuVO2 does not exist, the present study well confirms that large amounts of vanadium(III) can be incorporated into copper based delafossites without reducing Cu+ into metallic copper, as several solid solutions CuM1−xVxO2 exist where M=Ga, Cr (x⩽0.50) or Fe (x⩽0.67).Vanadium(III) has a peculiar magnetic behavior. Actually VV antiferromagnetic interactions appear rather large at high temperature, but as the temperature decreases magnetic data can be (at least qualitatively) interpreted assuming the formation of VV pairs. The bonding involves one of the two electrons of the 3d2 (a11e1) configuration of V(III)-atoms having a 6-fold D3d coordination, the one occupying the e orbital that lies in the (M, V) layers of the delafossite structure. The behavior changes from a rather 2D ferrimagnetic-like one to a 3D antiferromagnetic one with a Néel temperature larger than 4.5 K in the case of CuFe1−xVxO2 as determined from a Mössbauer study.
Zinc oxide (ZnO) nanoparticles were synthesized by a hydrothermal process at 120 ∘C. XRD results reveal that the sample product is crystalline with a hexagonal wurtzite phase. TEM results confirm that the morphology of the annealed ZnO is rod shaped with an aspect ratio (length/diameter) of ∼3.2. We also investigate the crystallite development in nanostructured ZnO by X-ray peak broadening analysis. The individual contributions of small crystallite sizes and lattice strain to the peak broadening in as-prepared and annealed ZnO nanoparticles were studied using Williamson-Hall (W–H) analysis. All other relevant physical parameters including strain, stress and energy density value were calculated more precisely for all the reflection peaks of XRD corresponding to wurtzite hexagonal phase of ZnO lying in the range 20∘–65∘, from the modified form of W–H plot assuming the uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM). The root mean square (RMS) lattice strain 〈εRMS〉calculated from the interplanar spacing and the strain estimated from USDM and UDEDM are different due to consideration of anisotropic crystal nature. The results obtained show that the mean particle size of ZnO nanoparticles estimated from TEM analysis, Scherer’s formula and W–H method are highly inter-correlated. All the physical parameters from W–H plot are tabulated, compared, and found to match well with the value of bulk ZnO.
We have calculated the superconducting critical temperature Tc of hole-doped delafossite CuAlO2 based on first-principles calculations. According our calculation, 0.2–0.3 hole-doped CuAlO2 can become a phonon-mediated high-Tc superconductor with Tc≃50K. In the hole-doped CuAlO2, the A1L1 phonon mode that stretches the O–Cu–O dumbbell has a strong interaction with electrons of the flat band in Cu 3d3z2−r2 and the O 2pz anti-bonding π-band.
The CuCr1−xRhxO2 series is investigated by X-ray diffraction, magnetization measurements and Raman spectroscopy on ceramic samples. It is found that a delafossite solid solution is maintained up to x=0.2 in CuCr1−xRhxO2. The small observed variation in cell parameters is consistent with the small difference between the ionic radii of Cr3+ and Rh3+. A significant broadening of X-ray reflections is observed and when analyzed using the Williamson–Hall relationship showed that the strain generated by Rh substitution is strongly anisotropic, affecting mainly (Cr,Rh)–O bonds in the ab plane. Room temperature Raman spectra displayed three main Raman active modes. All modes shift to lower frequency and undergo significant changes in intensity with increasing Rh content, showing the effect of Rh atoms on the M3+–O bond strength. The magnetic behavior of CuCr1−xRhxO2 samples was investigated as a function of temperature and applied field. At high temperature paramagnetic behavior, and at low temperature, evidence for weak ferromagnetism, reinforced by a hysteresis loop at 4K is observed. The magnetic behavior of CuCr1−xRhxO2 is attributed to the disorder of Cr and Rh in octahedral sites resulting in short-range Cr–O–Cr and Cr–O–Rh interactions, which give rise to short-range weak ferromagnetism.
A series of CuCr1−xNixO2 (0≤x≤0.06) polycrystalline samples was prepared. The electrical conductivity was measured in the temperature range of 160–300 K. It was found that the electrical conductivity (σ) increases rapidly with the doping of Ni2+ ions. At room temperature, the σ is 0.047 S cm−1 for the sample with x=0.06, which is two orders of magnitude larger than that of the CuCrO2 sample (9.49E−4 S cm−1). The Seebeck coefficients are positive for all samples, which indicate p-type conducting of the samples. The experimental results imply that it is possible to get higher electrical conductivity p-type transparent conducting oxides (TCO) from CuMO2 by doping with divalent ions.
We have performed pseudopotential calculations and x-ray-diffraction and x-ray-absorption measurements on the CuGaO2 delafossite under high pressure. We have completely characterized the structural behavior of the low pressure phase. We have found out that the a axis is more compressible than the c axis, and as a consequence the oxygen octahedra defined by the gallium environment tend to become more regular under high pressure. We have determined the internal parameter describing the oxygen position inside the unit cell, and seen that it is nearly constant when pressure is applied. We have observed an irreversible phase transition affecting the copper environment but not the gallium one. Such phase transition begins at 24±2 GPa and is completed at 28±2 GPa.
A comprehensive study of conduction polarons in purified BaTiO3 crystals, containing about 100-ppm Nb as extrinsic ions, is presented. Nb5+ is compensated by Ti3+ (3d1) ions, many of them isolated. Small Ti3+ polarons, stabilized by crystal strains, and polarons of intermediate size in less strained crystal regions are identified. Both species break the point symmetry, indicating stabilization by a tetragonal T2×e Jahn-Teller distortion. There is indirect evidence for the presence of bipolarons in the crystal ground state. They have a rather small dissociation energy, 0.01 eV. The investigations are based on electron paramagnetic resonance (EPR) performed at T<20K under application of uniaxial stress. This allows to obtain local information on the intrinsic Jahn-Teller properties of the conduction states of an oxide perovskite. For the small polarons stress has the following effects: (i) aligns the tetragonal Jahn-Teller axes along the stress direction, and (ii) enlarges the radius of the aligned orbitals, transforming them into intermediate ones. The stress alignment of the intermediate polarons is different: The Jahn-Teller axes orient perpendicular to the stress axis. Several of the polaron features are elucidated by comparison with the stress-dependent Jahn-Teller properties of the impurity ion Mo5+ (4d1), where the d electron is prevented from tunneling to its Ti4+ neighbors. The EPR of Ti3+ in reduced BaTiO3 is attributed to polarons bound to doubly filled oxygen vacancies.
We have studied the vibrational properties of CuAlO2 by means of Raman scattering in ambient conditions, at low temperature, and also at high pressure. Results are discussed in the framework of an ab initio calculation. Raman active modes have wave numbers σEg=418.1±0.2 cm−1 and σA1g=767.2±0.3 cm−1. Polarized measurements with single crystals have confirmed their symmetry. We present and discuss the phonon-dispersion curves. Below 200 K, the temperature dependence of the Raman active modes is almost linear, with coefficients ∂σEg∕∂T=(−4±1)×10−3 cm−1∕K and ∂σA1g∕∂T=(−1.0±0.2)×10−2 cm−1∕K. Most of the temperature shift is associated with thermal expansion. The pressure dependence is given by ∂σEg∕∂P=2.72±0.07 cm−1∕GPa and ∂σA1g∕∂P=4.96±0.12 cm−1∕GPa. We observe a reversible phase transition at 34±2 GPa, which, as already has been shown to happen in CuGaO2, we relate to the existence of a dynamical instability.
ZnO nanoparticles (ZnO-NPs) were prepared by a sol-gel combustion method from a zinc acetate precursor and acetic acid. The ZnO-NPs were synthesized at calcination temperatures of 650 degrees C and 750 degrees C for 1 h. The synthesized ZnO-NPs were characterized by X-ray diffraction analysis (XRD) and TEM. The XRD results revealed that the sample product was crystalline with a hexagonal wurtzite phase. High-magnification transmission electron microscopy (TEM) showed single-crystal ZnO-NPs with nearly spherical shapes. The crystalline development in the ZnO-NPs was investigated by X-ray peak broadening. The Williamson-Hall (W-H) analysis and size-strain plot method were used to study the individual contributions of crystallite sizes and lattice strain on the peak broadening of the ZnO-NPs. The physical parameters such as strain, stress and energy density values were calculated more precisely for all the reflection peaks of XRD corresponding to the wurtzite hexagonal phase of ZnO lying in the range of 20 degrees-100 degrees from the modified form of the W-H plot assuming a uniform deformation model (UDM), uniform stress deformation model (USDM), uniform deformation energy density model (UDEDM) and by the size-strain plot method (SSP). The results obtained showed that the mean particle size of the ZnO-NPs estimated from the TEM, W-H analysis and the SSP method were highly intercorrelated. (C) 2010 Elsevier Masson SAS. All rights reserved.
FTIR spectra of pure CuCrO 2 and doped samples
- Fig
Fig. 10. FTIR spectra of pure CuCrO 2 and doped samples.
Handbook of Chemistry and Physics, 58 th Ed
- R C Weast
R.C. Weast, Handbook of Chemistry and Physics, 58 th Ed., 1977, pp. 213e214.
Origin of giant dielectric constant in Ba[(Fe 1Àx Co x ) 1/2 Nb 1/2 ]O 3
- D Devang
- P K Shah
- M S Mehta
- C J Desai
Devang D. Shah, P.K. Mehta, M.S. Desai, C.J. Panchal, Origin of giant dielectric
constant in Ba[(Fe 1Àx Co x ) 1/2 Nb 1/2 ]O 3, J. Alloys Compd. 509 (2011) 1800e1808,
https://doi.org/10.1016/j.jallcom.2010.10.045.