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ln(σ dc ) vs. 1000/T of the system Ca 2 MnO 4−δ with δ = 0.0 (), δ = 0.15 (), δ = 0.2 (), δ = 0.3 (•) and δ = 0.4 (•).
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The materials Ca2MnO4−δ(δ=0.0–0.5) were prepared in two steps: the preparation of the parent compound Ca2MnO4 by the sol–gel method followed by the creation of oxygen vacancies δ. The morphology has been studied by scanning electron microscopy (SEM) technique and has revealed that the free surface morphology becomes more densified when increasing t...
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... with a Keithley electrometer, model 617, as a function of the temperature (100-370 K) and the impedance spectroscopy measurements were performed in the frequency range of 40 Hz-110 MHz using an Agilent 4294A, in the same temperature range. The dependence of the dc conductivity with the temperature, for the range between 290 and 360 K, is shown in Fig. 3, where the relation between ln(σ dc ) and 1000/T is linear and thus the Arrhenius equation (Eq. (2)) can be applied in order to obtain the activation energy of this conduction mechanism. The sample with δ = 0.5 is not shown because it presents a very low conductivity (<10 −12 S/m). The Arrhenius expression [11][12][13][14][15][16] used ...
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... a(ac) the activation energy for the relaxation process and k B the Boltzmann constant. In a logarithmic representation of F r as a function of the inverse temperature, linear fits are obtained, as we can observe in Fig. 9. The activation energy is independent of δ, with a value of 0.24 eV and lower than the observed for the dc conduction process (Fig. 3). Assuming the potential barrier model, these results indicate that the long range conduction process is more difficult that the short range. In Fig. 9 we can see the depression angle as a function of temperature for different values of δ. In general, higher values of δ present lower angles. ...
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Citations
... 43,44 However, to date, the sintering behavior of Ca 2 MnO 4 has been poorly studied in the published literature, and when investigated, it has generally been badly controlled. [45][46][47] Consequently, there is considerable interest in comprehensively understanding the sintering mechanisms of this compound to enable the production of bulk materials with controlled density and microstructure. ...
n‐type Dy‐doped Ca2MnO4 powders with the Ruddlesden–Popper structure were synthesized by the combustion method and sintered by conventional sintering and spark plasma sintering (SPS). Conventional sintering fails to densify Ca2MnO4, but the addition of Li2O proves to be a highly effective sintering additive, albeit with a detrimental impact on electrical conductivity. In contrast, SPS at 850°C for 1 min yields nanostructured, nearly fully dense samples, demonstrating superior outcomes. The dimensionless figure of merit ZT reaches 0.02 at 750°C. Additionally, the best sample exhibits a remarkable hardness value of 10.7 GPa, underlining the excellent mechanical properties achieved through this innovative approach.
... Moreover, the n = 1 RP oxides allow a wide range of oxygen stoichiometries, from oxygen-stoichiometric to oxygen-deficient and oxygen-excess, depending on the oxygen defects (Chihaoui et al. 2011a;Yang et al. 2019). Similar to other members of the RP family, the Ca 2 MnO 4 perovskite exhibits various magnetic, dielectric, and thermoelectric properties (Tezuka et al. 1999;Matar et al. 2005;Chihaoui et al. 2011bChihaoui et al. , 2013Baranovskiy and Amouyal 2016). Furthermore, its layered structure and non-toxic and readily available chemical constituents make it a promising material for new battery cathodes (Surace et al. 2014). ...
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... The values of E a are determined via the slope of Ln (σ dc .T) versus 1000/T in Fig. 5c. For the temperature range between 300 to 380 K the value of E a1 = 0.175 eV and E a2 = 0.356 eV for the temperature range between 400 to 500 K; these values are similar to these of the E a in the spinel ferrites [58]. The mechanism behind conduction in nanoferrites has been explained using Verwey and De Boer's theory [59], which proposes that electrons exchange between identical-element ions that have different valence states. ...
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Graphical Abstract
Sol–gel synthesis steps for Co0.6Zn0.4Fe2O4 ferrite.
... Note that the activation energy of grain resistance (from the model) is in good agreement with that the calculated from DC conductivity, implying that electrical mechanisms are dominantly associated with the grain effect. In addition, the activation energies obtained in this work are comparable to those for other perovskite compounds based on manganese [14,23]. The conduction and relaxation mechanism for all compositions are thermally activated and satisfies the Arrhenius law. ...
Herein, we investigated the structural, optical, and dielectric properties of perovskite LaFe1−xMnxO3 (x = 0.00, 0.05, 0.10, 0.15, and 0.20) polycrystalline ceramics synthesized using sol–gel and sintering methods. X-ray diffraction measurements revealed that these materials adopt a single-phase orthorhombic crystal structure (space group Pnma). The effects of the Mn substitution induce changes in the lattice parameters including the Fe/Mn–O–Fe/Mn bond angle, Fe/Mn–O bond length, and tilting of the bond angle; these changes are also supported by the tolerance factor calculations and Raman scattering analysis. The complex impedance of the samples was measured in the temperature range of 100 °C to 275 °C and over the frequency range of 100 Hz to 1 MHz. The Nyquist plots, i.e., Z″ versus Z′ over the entire frequency range, resembled semicircular arcs and could be described by an electrical equivalent circuit model. The complex conductivity of the samples was investigated using both the equivalent circuit modelling and the Jonscher universal power law. The activation energies of the conduction processes obtained from both methods were very similar, indicating that the model comprising discrete electrical components used to interpret the response of the real system is applicable. The activation energies from conduction and relaxation processes were found to be < 1 eV, indicating that the mechanisms might be predominantly induced by oxygen ionic conductivity rather than electronic conductivity and oxygen vacancies.
... To calculate the activation energies, we use the Arrhenius law. The variation of relaxation frequency (f max ) with temperature can be expressed by Eq. (1) [32]: ...
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... The activation energy of the dielectric relaxation process was determined using the Arrhenius law. The variation of relaxation frequency (f max ) with temperature can be expressed by Eq. (2) [44]: ...
... The best fit was obtained when using an (R 1 /CPE 1 )-(R 2 /CPE 2 ) equivalent circuit (see the insets of Fig. 6) according to C. Chen et al. [29]. The CPE impedance (Z CPE ) is given by the following relation [30]: ...
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... The frequency dependence of imaginary part of the electric modulus (M 00 ) for all the samples are displayed in Fig. 14. The electric modulus formalism was used to investigate ionic conductivities and dielectric relaxation mechanisms, because it minimizes the electrode interface capacitance contribution and other interfacial effects [25]. All the composites exhibit relaxation peaks at different frequencies due to interfacial polarization. ...
Carbon based materials with a high dielectric performance and better thermal stability have great potential for many semiconductor device applications. In this paper, we report the preparation, thermal and dielectric properties of multi-walled carbon nanotube (MWCNT)–graphene oxide (GO) freestanding films. Different weight percentages of MWCNT–GO composite freestanding films were prepared using vacuum filtration method. Powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared, micro Raman and UV–Vis–NIR spectroscopy studies revealed that the homogeneous dispersion of MWCNT in the GO matrix. Thermal stability of the MWCNT–GO composites linearly increases with increasing MWCNT content from 5 to 30 wt%. Our results show that the addition of 30 wt% MWCNT in GO increases the dielectric constants from 17 to 807 at 100 Hz which was even very high compared to conventional dielectric materials. The improvement of dielectric constant is attributed to the formation of microcapacitors by highly conductive MWCNT segregated by GO sheets. Meanwhile, the Cole–Cole plot elucidates the two semicircles for all samples representing the serial arrangement of two units that attributed to the contribution from the bulk composite and the interface region of the MWCNT–GO. The radius of arc in impedance spectra decreases with increasing MWCNT weight percentage indicating the higher electrical conductivity. The present results suggest that MWCNT–GO composite films are having promising application in the high frequency capacitors, high performance dielectric based electronic and energy storage devices.
... It also minimizes the electrode interface capacitance contribution and other interfacial effects. 26 The electric modulus corresponds to the relaxation of the electric field in the material when the electric displacement remains constant. Figure 6 shows real (M¢) and imaginary (M¢¢) parts of the complex modulus plots as a function of angular frequency at different temperatures. ...
The electrical properties of rare-earth based ordered double perovskite oxide barium erbium tantalate, Ba2ErTaO6 synthesized by solid-state reaction method are investigated. The x-ray diffraction pattern of the sample shows cubic Fm3m phase at room temperature with ordering of the B cations. Fourier transform infrared spectrum shows two primary phonon modes of the sample at around 350 cm−1 and 600 cm−1. The dielectric relaxation of the sample is investigated in the frequency range from 50 Hz to 1.1 MHz and in the temperature range from 303 K to 673 K. Electric modulus and electrical impedance data are fitted to the Cole–Cole equation. The frequency dependent conductivity spectra follow the power law. Summerfield scaling is used to explain the conduction mechanism. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures. The complex impedance plane plots show that the relaxation (conduction) mechanism in this material is mainly due to grain boundary effect for all temperatures and grain effect for low temperature. The relaxation frequency corresponding to dielectric loss is found to obey Arrhenius law with activation energy of 0.50 eV. The values of activation energy indicate that the dielectric relaxation and the conduction mechanism are due to adiabatic small polaronic hole hopping mechanism.
... This method describes the electrical processes occurring in a system on applying an ac signal as an input perturbation. This technique has been applied to analyze the relaxation spectrum of many bulk materials [7][8][9][10]. ...
... Moreover, to the best of our knowledge, there are no reports on structural and electrical properties of BaPr-CoNbO 6 (BPCN) till date. In particular, the presence of both SOJT distortions of d 0 cations and the presence of magnetic ions make BPCN potentially attractive candidate for various technological applications such as microelectronics, telecommunications, memory devices, and charge storage devices [1][2][3][4][5][6][7][8][9][10]. Also the possible ordering of B-cations namely Co 2 þ and Nb 5 þ should make this compound more interesting for investigating its structural detail. ...
A new rare earth based double perovskite oxide barium praseodymium cobalt niobate, BaPrCoNbO6 (BPCN) is synthesized by solid-state reaction technique. Rietveld analysis of X-ray diffraction (XRD) data shows that the compound crystallizes in a perovskite like tetragonal structure which belongs to the I4/mmm space group with lattice parameters a=b=5.6828(9) Å, c=8.063(2) Å. Structural analysis reveals 1:1 ordered arrangement for the Co2+ and Nb5+ cations over the six-coordinate B-sites of BPCN. The superlattice line (101) at 2θ=19.10° arising from the alternate ordering of Co2+ and Nb5+ sites is observed in the XRD pattern which confirms the presence of cation ordering in BPCN. Fourier transform infrared spectrum shows two phonon modes of the sample due to the antisymmetric NbO6 stretching vibration. The relaxation dynamics of the conductive process in BPCN is investigated in the temperature range 303 to 503 K and in the frequency range 100 Hz to 1 MHz using impedance spectroscopy. The relaxation mechanism of the sample in the framework of electric modulus formalism is modeled by Davidson-Cole model (DCM). The values of α (distribution of relaxation time) for the DCM varies from 0.1 to 0.3 which suggests the asymmetric distribution of relaxation time for BPCN. The activation energy of the sample, calculated from both conductivity and modulus spectra, are found to be almost the same ∼0.4 eV, which indicates that the conduction mechanism for BPCN is polaron hopping. The scaling behaviour of the imaginary part of electric modulus suggests that the relaxation follows the same mechanism at various temperatures.
