The temperature dependence of dielectric properties and electrical conduction of (Sr 1Ϫ1.5x Bi x )TiO 3 (0.0133рxр0.133) was measured from 10 to 800 K. Three sets of oxygen vacancies related dielectric peaks ͑peaks A, B, and C) were observed. These peaks could be greatly suppressed or eliminated by annealing the samples in an oxidizing atmosphere, and enhanced or recreated by annealing in a reducing atmosphere. The results show that the Maxwell-Wagner polarization is not the main mechanism, and the Skanavi's model also cannot be directly applied. A tentative explanation was suggested. Peak A, observed in the temperature range of 100-350 K with the activation energy for dielectric relaxation E relaxA ϭ0.32-0.49 eV, is attributed to the coupling effect of the conduction electrons with the motion of the off-centered Bi and Ti ions; the conduction carriers in this temperature range are from the first ionization of oxygen vacancies (V o ). Peaks B and C are also discussed.

No abstract

Hybrid inorganic-organic perovskites have proven to be a revolutionary material for low-cost photovoltaic applications. They also exhibit many other interesting properties, including giant Rashba splitting, large-radius Wannier excitons, and novel magneto-optical effects. Understanding these properties as well as the detailed mechanism of photovoltaics requires a reliable and accessible electronic structure, on which models of transport, excitonic, and magneto-optical properties can be efficiently developed. Here we construct an effective-mass model for the hybrid perovskites based on the group theory, experiment, and first-principles calculations. Using this model, we relate the Rashba splitting with the inversion-asymmetry parameter in the tetragonal perovskites, evaluate anisotropic g-factors for both conduction and valence bands, and elucidate the magnetic-field effect on photoluminescence and its dependence on the intensity of photoexcitation. The diamagnetic effect of exciton is calculated for an arbitrarily strong magnetic field. The pronounced excitonic peak emerged at intermediate magnetic fields in cyclotron resonance is assigned to the 3D±2 states, whose splitting can be used to estimate the difference in the effective masses of electron and hole.

The polarization and strain behavior of Ba(Ti1−xZrx)O3 (x=0–0.3) ceramics are studied. The unipolar strain levels of ∼0.18% at 40 kV/cm and of ∼0.25% at ∼120 kV/cm with small hysteresis were obtained for the ceramics with 0.03⩽x⩽0.08. The remnant polarization is ∼13–18 μC/cm2 for 0.03⩽x⩽0.08 and below 2 μC/cm2 for 0.15⩽x⩽0.3 at room temperature. The electromechanical coupling coefficient K33=56.5% and the piezoelectric stain coefficient d33=236 pC/N were obtained for the ceramics with x=0.05. These results indicated that the Ba(Ti1−xZrx)O3 system is a promising lead-free high strain material for applications.