Yue Jin Shan

Dielectric Behavior of (1-x)LaAlO3–xSrTiO3 Solid Solution System at Microwave Frequencies

The (1-x)LaAlO3–xSrTiO3 solid solution system with the perovskite structure was synthesized and its dielectric behavior was investigated. The lattice parameter of (1-x)LaAlO3–xSrTiO3 increases with increasing the fraction of SrTiO3 in the system. 0.45LaAlO3–0.55SrTiO3 shows a dielectric constant e of 34, a temperature coefficient of resonant frequency τf of -8 ppmK-1 and a dielectric loss Q of 6900, which satisfy the suggested requirements for applications to mobile communications devices. The annihilation of the ferroelectric mode of SrTiO3 corresponds to the drastic decrease of e and τf of SrTiO3 to those of 0.25LaAlO3–0.75SrTiO3.

Oxide cathode with perovskite structure for rechargeable lithium batteries

Lithium ions were electrochemically inserted into perovskite-type oxides SrVO3−δ and La0.50Li0.37TiO2.94 using galvanic cell: Li|1 M LiClO4 in PC|SrVO3−δ or La0.50Li0.37TiO2.94. It is found that the lattice parameters of SrVO3−δ will be increased and the discharge capacity of SrVO3−δ will be decreased as δ increased. At the composition where all of A-site vacancies in La0.50Li0.37TiO2.94 are just occupied by the lithium ions, the lattice parameter shows a sudden increase. The chemical diffusion coefficients of lithium ions in SrVO3−δ and La0.50Li0.37TiO2.94 were determined to be the values in the range from 10−8 to 10−12 cm2 s−1. Both oxides can be considered as a useful cathode of rechargeable lithium batteries. The charge/discharge characteristic can be improved by mixing of a small amount of carbon powder with the oxide.

Crystal structure and characterizations of perovskite oxides (Eu1−xSrx)MnO3 (0.0≤x≤0.5)

Abstract Novel perovskite-type oxides (Eu 1− x Sr x )MnO 3 (0.0≤ x ≤0.5) have been prepared by the conventional solid-state technique. Synthesized samples still have orthorhombic symmetry with space group Pnma throughout the range studied. The crystal symmetry and conductivity of (Eu 1− x Sr x )MnO 3 (0.0≤ x ≤0.5) became higher with increasing x , but the metal–insulator transition was not observed. EuMnO 3 is antiferromagnetic with T N ≈55 K. Samples with x =0.2 and x =0.4 show ferromagnetic behaviors with T c ≈120 K and ≈130 K, respectively. The relationships between the magnetic properties and the crystal structure are investigated through the detailed study of crystal structure.

Preparation and dielectric characterizations of the novel perovskite-type oxides (Ln1/2Na1/2)TiO3 (Ln=Dy, Ho, Er, Tm, Yb, Lu)

The novel perovskite-type oxides (Ln 1/2 Na 1/2 )TiO 3 (Ln = Dy, Ho, Er, Tm, Yb, Lu) were synthesized, and their crystal structures and dielectric properties were examined. (Ln 1/2 Na 1/2 )TiO 3 (Ln = Dy, Ho, Er, Tm, Yb, Lu) possess an orthorhombic symmetry with space group Pnma similar to (Ln 1/2 Na 1/2 )TiO 3 (Ln = Pr, Nd, Sm, Eu, Gd and Tb). Their lattice parameters and dielectric constants decrease with an increase in the atomic number of Ln (Ln = Dy to Lu). At low temperatures, (Ln 1/2 Na 1/2 )TiO 3 (Ln = Dy, Ho, Er, Tm, Yb, Lu) shows quantum paraelectric behavior.

On the perovskite-related materials of high dielectric permittivity with small temperature dependence and low dielectric loss

Abstract Dielectric properties of quantum paraelectric materials, SrTiO3, CaTiO3 and (La1/2Na1/2)TiO3, were presented and discussed since they show the titled dielectric properties in the lowest te...

Transparent conductive Cd3TeO6 thin films with perovskite structure

Transparent conductive Cd3TeO6 thin films were deposited by radio-frequency magnetron sputtering using a target composed of CdO and TeO2 powders, and these films’ electrical and optical properties were examined. The electrical resistivity of 1.9×10−2Ωcm and an average transmittance above 85% in the visible region (400–800 nm) were obtained after annealing the film at 500 °C. The film’s carrier density and Hall mobility were 8.7×1019cm−3 and 6.8cm2V−1s−1, respectively. The absorption edge of the films was shifted to a lower wavelength by increasing the carrier density. The maximum band gap of these films was found to be 3.69 eV.

Ferroelectric Phase Transition in Perovskite Oxide CdTiO 3

Single crystals of CdTiO 3 were synthesized by a flux method. The obtained single crystals showed the orthorhombic perovskite structure with the space group Pnma at room temperature, and a dielectric anomaly appeared near 80 K, which was similar to the polycrystalline samples. The temperature dependence of the dielectric constants along three directions was investigated, and a dielectric anisotropy was observed. The comparison of the measured dielectric constants indicates that the polarization of CdTiO 3 is directed along the b axis of the space group Pnma .

New n-Type Thermoelectric Oxide, Cd3TeO6

Electron doping into Cd3TeO6 with a 1:1 ordered perovskite-type structure was carried out by two methods: the introduction of oxygen vacancies, and the atomic substitution of In for Cd. Both methods turned polycrystalline samples into metallic conductors while single crystals with metallic conductivity were obtained by the second method. The resistivity and thermoelectric power of the single-crystal indium-substituted sample were 0.6 mΩcm and -50 µVK-1, respectively, giving a power factor of 4×10-4 WK-2m-1, which is the highest among nontransition metal oxides.

The effect of electrostatic potentials on lithium insertion for perovskite oxides

Abstract Lithium was electrochemically inserted into perovskite oxides, SrVO 3 − δ , La 2 3 TiO 3 − δ and (La, Li)TiO 3 − δ , by using a galvanic cell: Li ¦1M LiClO 4 in PC ¦perovskite oxide. The tetravalent transition metal ion (Ti, V) can be reduced to the minimum valence of 3 by lithium insertion. This fact was explained by the effect of valence on the lattice self-potential and site-potential in the ideal perovskite oxide ABO 3 . We tried to explain the lithium insertion and high lithium conductivity in the perovskite oxide from the view point of electrostatic potentials.

The study on the dielectric property and structure of perovskite titanate CdTiO3

Abstract The anomalous peak in dielectric constant versus temperature of perovskite CdTiO3 appears at 77 K, which corresponds to the nonlinear D-E hysteresis loop below 80 K. The powder X-ray diffraction profiles at room temperature and 15 K do not change evidently. The indices of the diffraction profiles satisfy the extinction rule of both centrosymmetric space group Pnma and noncentrosymmetric Pna21. In the case of profiles at 15 K, the R factors of Rietveld refinement by Pnma or Pna21 reveal nearly the same satisfactory Values. No differences can be distinguished between the Raman spectra at room temperature and 4K. Although X-ray diffraction profiles and Raman spectra can not provide any effective structural differences, the D-E hysteresis loop suggests that a transition from centrosymmetric space group Pnma to noncentrosymmetric Pna21 may exist.