Y. Q. Ma

Anhui University, Luchow, Anhui Sheng, China

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Publications (46)74.83 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The irreversible susceptibilities χirr (H) exhibited the double-peak behavior which can be assigned to the cation vacancies in SrFe12O19. The coercivities Hc of all samples almost changed linearly with the average value Hirr of irreversible fields (peak position of χirr), indicating that the coercivity was mainly determined by the amount and distribution of cation vacancies in SrFe12O19.
    Materials Research Bulletin 09/2014; 57:13–18. · 1.97 Impact Factor
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    ABSTRACT: We investigated the effects of Ag added Sr0.9La0.1TiO3 ceramics prepared via a hydrothermal method and sintering. The results indicate that Ag addition is an efficient way to enhance its thermoelectric properties. The maximum thermoelectric figure-of-merit, ZT, is 0.20 at 955 K for x=0.15 sample.
    Journal of Low Temperature Physics 02/2014; 174(3-4). · 1.18 Impact Factor
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    ABSTRACT: YBO3:Eu3+ phosphors with different morphologies such as flower-like, spherical-like and cake-like have been hydrothermally synthesized without any additives by simply adjusting the B3+ sources, stirring speeds and initial solution pH values. During the hydrothermal reaction, stirring with suitable speed can reduce particle size and obtain more uniform size distribution. The emission intensity can be distinctly enhanced by stirring and post-annealing due to the micro-structural improvement and better crystallization. Interestingly, the weak acidity (pH = 6) in the initial solution or post-annealing enhances the emission in the wavelength range of visible light, and weakens the emission around 700 nm due to weakened distortion of the outside surroundings of Eu3+, which is useful in Plasma Display Panel (PDP) application.
    Journal of Alloys and Compounds 10/2013; 574:142–148. · 2.73 Impact Factor
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    ABSTRACT: Ruddlesden-Popper (RP) phase (Sr0.9La0.1)3Ti2O7/xAg (x=0, 0.05, 0.10, 0.15) are systematically investigated with regard to their phase composition and thermoelectric transport properties. The XRD results show that all oxide samples are of two phases and they have layered microstructure. The electrical conductivity is found to be increased simultaneously. And the absolute Seebeck coefficient decreases firstly and then increases Ag addition, which leads to (Sr0.9La0.1)3Ti2O7/xAg (x=0.10) sample possesses optimum power factor. The total thermal conductivity lowers with Ag addition. The dimensionless figure of merit, ZT, reaches 0.12 for x=0.10. These results suggest that a proper of metal element Ag addition would be an effective way improving thermoelectric performance of (Sr0.9La0.1)3Ti2O7 system.
    Journal of Low Temperature Physics 06/2013; · 1.18 Impact Factor
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    ABSTRACT: CoFe2O4/Co0.7Fe0.3 nanocomposite permanent magnets have been synthesized in one step by a hydrothermal method at reaction temperatures of 80, 120, 140, 160 and 180 °C and characterized by XRD, SQUID, SEM, (HR)TEM, and SAED. All samples consisted of octahedral CoFe2O4 particles and spherical-like Co0.7Fe0.3 particles. The maximum magnetization and coercivity were 191 emu/g and 1311 Oe, respectively, values not previously observed for the CoFe2O4/Co0.7Fe0.3 system. This maximum magnetization was attributable to the larger mass ratio of Co0.7Fe0.3 to CoFe2O4, which were in intimate contact. Magnetic dipolar interaction plays a crucial role in magnetic properties and leads to the reduction of the magnetization and the Mr/Ms ratio. The coercivity of all samples exhibited complex variation with reaction temperature and its mechanism may deserve further investigation.
    ChemInform 04/2013; 553:79–85.
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    ABSTRACT: Systematical studies of resistivity ρ(T), thermopower S(T), and thermal conduction κ(T) have been performed on the electron-doped manganites La0.9Te0.1Mn1−x Cr(Al) x O3 (0.05≤x≤0.20). The Cr005 and Al005 samples exhibit an insulator-metal transition in the ρ(T) curves, however, other samples present insulating behaviors in the whole measured temperature. The S(T) data increases with decreasing temperature and develop a peak at TSPT_{S}^{P} for all samples, with decreasing temperature further, another characteristic temperature TsmT_{s}^{m} is observed. The fits of ρ(T) and S(T) data in the high temperature region are presented, and the result shows that the electron conduction is governed by the VRH mechanism for Al-doped samples and the SPC mechanism for Cr-doped ones. As to thermal conduction κ(T), it is suggested that it comes from two sides, one is the phonon-phonon scattering due to disorder and the other is the spin-phonon interaction. KeywordsThermoelectric power–Transport mechanism–Thermal conductivity
    Journal of Low Temperature Physics 10/2011; 165(1):43-54. · 1.18 Impact Factor
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    ABSTRACT: Composition dependence of interface control, band alignment and electrical properties of HfTiON/Si grown by sputtering has been studied by spectroscopy ellipsometry (SE), x-ray photoelectron spectroscopy (XPS) and electrical measurement. Analysis from XPS has confirmed that the interfacial layer consisting of silicate and SiOx is formed unavoidably, irrespective of composition ratio. Meanwhile, reduction in band gap and asymmetric band alignment has been detected for HfTiON films with the increase in Ti composition. To meet the requirements of high-k dielectrics with the barrier height of over 1 eV, the incorporation composition ratio needs to be carefully optimized. As a result, improved C–V characteristics and reduced leakage current have been achieved from HfTiON gate dielectric MOS capacitors with optimized composition ratio of Hf:Ti = 1:1, which can be attributed to the reduction in oxygen-related traps and the obtained near-symmetric band alignment relative to Si.
    Semiconductor Science and Technology 09/2011; 26(10):105019. · 1.92 Impact Factor
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    ABSTRACT: Photoluminescence properties of Sr3(VO4)2, Sr2Y2/3−yEuy(VO4)2 and Sr2Y2/3−zSmz(VO4)2 (y, z = 0, 0.1, 0.2, and 0.3) samples have been investigated. The self-activated Sr3(VO4)2 sample shows the activation and emission bands due to the charge transfer transition of VO43-. While Sr2+ is partially substituted by Y3+, Sr2Y2/3 (VO4)2 can be used as the good host material for Eu3+ and Sm3+ activator-ions. The Eu3+ and Sm3+ ions doped Sr2Y2/3(VO4)2 can be effectively excited by the near UV light with wavelengths of 300 nm, and emit red light around 617 and 604 nm, respectively. Specially, for Sr2Y2/3−yEuy(VO4)2, Y3+ substitution quite enhances the emission intensity and quenching concentration of Eu3+. For example, Sr2Y0.56Eu0.1(VO4)2 has higher emission intensity than Sr2.85Eu0.1(VO4)2 without Y3+, and even much higher than Y1−xEuxVO4 which has been extensively used. Our results suggest that Sr2Y2/3−yEuy(VO4)2 samples may be good candidate for a new phosphor to convert the UV pump light into visible wavelength bands.
    Optical Materials 01/2011; 33:1162-1166. · 2.08 Impact Factor
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    ABSTRACT: The luminescent properties of Sr3V2−xPxO8 (0 ⩽ x ⩽ 2), Eu3+ doped Sr2.7Eu0.2V2−yPyO8 (0 ⩽ y ⩽ 2) and Sr3−3zEu2zV0.8P1.2O8 (0 < z ⩽ 0.3) have been investigated. For the Sr3V2−xPxO8 (0 ⩽ x ⩽ 2) samples, the VO43- activation and emission intensity reaches the strongest as x = 1.6. For the Sr2.7Eu0.2V2−yPyO8 (0 ⩽ y ⩽ 2) samples, an appropriate amount of phosphorus doping enhances the Eu3+ emission with the strongest emission occurring at y = 1.2. For the Sr3−3zEu2zV0.8P1.2O8 (0 < z ⩽ 0.3) sample with the phosphorus content fixed at 1.2, it exhibits the most intense emission as Eu3+ concentration reaches at z = 0.2. Our results indicate that the introduction of the PO43- plays an important role in the photoluminescence properties of the studied samples and the relevant mechanism has been discussed.
    Optical Materials 01/2010; 32(9):1256-1260. · 2.08 Impact Factor
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    ABSTRACT: The optical spectra have been investigated for a prototypical double exchange ferromagnetic La0.67Ca0.33MnO3 with Mn substituted by V above the paramagnetic–magnetic transition temperature TC. The excitation spectra under the probe wavelength of λem = 473 nm for all samples exhibit two activation bands around 360 and 294 nm, involving an electron transfer from oxygen 2p states to the Mn d states in MnO6 octahedra. The photoluminescence spectra at λex = 290 nm have the similar spectral features for all samples. The photoluminescence spectral peaks located at 400, 473, 534, 670, 738 and 770 nm, and the corresponding photon energy is in a broad range of 3.1–1.6 eV, indicating that the PL bands could have the different origin: the self-trapped excitons localized on MnO6 octahedra; the interband transition between the O 2p and Mn 3d bands; the transition between the 3d electron states of Mn ions. So, it can be clearly seen that the electronic behavior above TC is very complicated. Our results suggest that the charge transfer from O 2p to Mn 3d has the important effects on the electronic structure, and it not only contributes to the optical transition but is helpful and even important to understand the electric, magnetic and thermal properties etc. due to the strong correlation among charge, spin and lattice in perovskite manganites.
    Materials Research Bulletin. 09/2009; 44(9):1867–1870.
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    ABSTRACT: The V doped La0.67Ca0.33Mn1−xVxO3 (0 ≤ x ≤ 0.08) samples have been investigated by measuring the resistivity, magnetization, thermoelectric power and thermal conductivity. The V doping lowers the metal–insulator and magnetic transition temperature and enhances the thermoelectric power. The evolution of thermal conductivity with temperature exhibits a similar characteristics as reported previously. For the x = 0.04 sample, the transport behavior somewhat appears to be anomalous, and it is suggested to result from the competing interaction among the multiple effects due to the V doping.
    Journal of Alloys and Compounds 01/2009; 482:535-539. · 2.73 Impact Factor
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    ABSTRACT: The optical spectra have been investigated for a prototypical double exchange ferromagnetic La0.67Ca0.33MnO3 with Mn substituted by V above the paramagnetic–magnetic transition temperature TC. The excitation spectra under the probe wavelength of λem=473nm for all samples exhibit two activation bands around 360 and 294nm, involving an electron transfer from oxygen 2p states to the Mn d states in MnO6 octahedra. The photoluminescence spectra at λex=290nm have the similar spectral features for all samples. The photoluminescence spectral peaks located at 400, 473, 534, 670, 738 and 770nm, and the corresponding photon energy is in a broad range of 3.1–1.6eV, indicating that the PL bands could have the different origin: the self-trapped excitons localized on MnO6 octahedra; the interband transition between the O 2p and Mn 3d bands; the transition between the 3d electron states of Mn ions. So, it can be clearly seen that the electronic behavior above TC is very complicated. Our results suggest that the charge transfer from O 2p to Mn 3d has the important effects on the electronic structure, and it not only contributes to the optical transition but is helpful and even important to understand the electric, magnetic and thermal properties etc. due to the strong correlation among charge, spin and lattice in perovskite manganites.
    Materials Research Bulletin - MATER RES BULL. 01/2009; 44(9):1867-1870.
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    ABSTRACT: We have investigated the phase-separated La0.5Ca0.5MnO3−δ samples, with the coexistence of ferromagnetic metallic and antiferromagnetic charge-ordered phases at low temperatures, by means of in-situ measurements of resistivity and Young's modulus combined with magnetization measurement. When the percolative metal–insulator transition occurs or the ferromagnetic domains grow up with decreasing temperature, the Young's modulus exhibits the corresponding variation. Our results suggest that the temperature-driven strain has a close correlation with basic physics such as the percolative metal–insulator transition and phase separation, etc.
    Physica B Condensed Matter 01/2008; 403(21):4100-4103. · 1.28 Impact Factor
  • Y. Q. Ma, Z. Q. Sun, M. Z. Wu
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    ABSTRACT: We report the electroresistance (ER) effect tuned by oxygen stoichiometry in La0.5Ca0.5MnOz. ER value varies from positive to negative, and is enhanced with the absolute maximum approaching a percentage of several thousands with lowering of the oxygen content, and the underlying physical mechanism of ER effect varies with the oxygen stoichiometry. We give a reasonable explanation on the mechanism of ER effect for the self-doped La0.5Ca0.5MnOz. In addition, the observation of the ER effect tuned by oxygen content may open up new routes to potential applications.
    Solid State Communications 01/2007; 143:245-249. · 1.53 Impact Factor
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    ABSTRACT: The effects of V doping on field-cooled magnetization MFC(T), zero-field-cooled magnetization MZFC(T), resistivity ρ, thermoelectric power S, and thermal conductivity κ in manganites CaMn1−xVxO3 (0.02 ⩽ x ⩽ 0.08) have been investigated systematically. As the V doping level exceeds 0.02, an anomalous “diamagnetism” has been observed. It is suggested that the force generated by the orbit rotation of eg electron in Mn3+O6 octahedron makes the spin tilt, as a result, the vector sum of individual spins may be along or opposite to the direction of the applied magnetic field, and macroscopically, the average magnetization exhibits positive or negative values. In addition, the transport mechanism in the high and low temperature ranges is dominated by the small polaron conduction and the variable-range-hopping conduction, respectively, according to the fitting analysis of the temperature dependence of Seebeck coefficient S(T) and resistivity ρ(T). Both S and κ peaks appearing at low temperature is gradually suppressed by V doping. Additionally, obvious magnetothermoelectric power and magnetothermal conductivity are observed in the temperature region which an anomalous diamagnetism appears. The results are discussed based on spin-orbital coupling and spin-phonon coupling induced due to V doping, respectively. Moreover, the large thermoelectric figure of merit Z = S2/ρκ for the slightly V-doped sample suggests that the V-doped manganite may be a good candidate for thermoelectric materials.
    Journal of Applied Physics 09/2006; 100(6):063902-063902-11. · 2.21 Impact Factor
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    ABSTRACT: The low temperature magnetic properties of the La0.275Pr0.35Ca0.375MnO3 manganite have been investigated. Step-like charge ordered antiferromagnetic (AFM)–ferromagnetic (FM) transition is observed in the magnetic field dependence of magnetization M(H) curve below 200 K as the applied magnetic field is only several Tesla, and the magnetic step become ultrasharp at 2 K. The onset magnetic field of the step decreases initially and then increases with increasing temperatures and the critical magnetic field is sensitive to the magnetic history. The results are discussed according to the field-induced reduction of the distortion of MnO octahedron as martensitic mechanism. The magnetic phase diagram is also constructed based on the magnetic measurements.
    Physics Letters A 06/2006; 354(5):472-476. · 1.63 Impact Factor
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    ABSTRACT: Well-oriented LaSr2Mn2O7 thin film with layered perovskite structure was fabricated via the magnetron sputtering method on an a-axis oriented SrTiO3 single crystal substrate. It exhibits large magnetoresistance and photoinduced decrease in resistance at low temperature. The study of the influence of the current, magnetic field and laser illumination on the charge-ordering (CO) state shows that the CO state at low temperature is sensitive to the external stimulus. The decrease in resistance is attributed to the relaxation of MnO6 octahedra distortion under the laser illumination as well as the magnetic field.
    Journal of Physics D Applied Physics 02/2006; 39(4):621. · 2.53 Impact Factor
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    ABSTRACT: The structure, resistivity, thermopower, and magnetization of the sample La0.9Te0.1MnO3 were investigated. The sample with a rhombohedral structure (R3¯C) undergoes the paramagnetic–ferromagnetic (PM–FM) transition accompanied by an insulator–metal (I–M) transition. Above the I–M transition temperature, a significant difference between the resistivity activation energy (Eρ=128.3 meV) and the thermopower activation energy (ES=14.7 meV), a characteristic of small polarons, is observed. In the PM region, the inverse magnetic susceptibility, 1/χm, is well described by the Curie–Weiss law indicating the absence of the short-range magnetic correlations, which further confirm that the conductivity above the I–M transition temperature for La0.9Te0.1MnO3 is indeed dominated by hopping of the lattice ‘small-polaron’ rather than hopping of the magnetic ‘small-polaron’.
    Materials Letters - MATER LETT. 01/2006; 60(27):3281-3285.
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    ABSTRACT: We have studied the perovskite manganite CaMn1-xV xO3 samples (0
    Solid State Communications 01/2006; 140:416-421. · 1.53 Impact Factor
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    ABSTRACT: The sensitivity of transport and the lattice to a direct current has been investigated by means of in situ measurements of resistivity varrho and Young's modulus E along with magnetic measurements in La0.67-yPryCa0.33MnO3 (y = 0, 0.15, 0.25, and 0.30) compounds. Increasing the Pr doping level enhances the softening of the magnitude of E with the appearance of a minimum in the curve of the temperature dependence of the modulus, E(T). The direct current depresses the resistivity and shifts the E(T) minimum to lower temperatures dramatically for the compounds with y ? 0.25, which exhibit a distinct magnetic hysteresis loop. The resistivity drop caused by the larger current may result from the depression of the Q3-type distortion mode of Mn3+O6 octahedra by the current, which may favor the lower resistivity.
    physica status solidi (b) 01/2006; 243:677-684. · 1.49 Impact Factor

Publication Stats

170 Citations
74.83 Total Impact Points

Institutions

  • 2006–2011
    • Anhui University
      Luchow, Anhui Sheng, China
  • 2004–2006
    • Chinese Academy of Sciences
      • Key Laboratory of Materials Physics
      Beijing, Beijing Shi, China
    • Northeast Institute of Geography and Agroecology
      • Key Laboratory of Materials Physics
      Beijing, Beijing Shi, China
  • 2003–2005
    • Nanjing University
      • Department of Physics
      Nan-ching, Jiangsu Sheng, China