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Sintered composites of iron oxide plus barium titanate in form of core-shell structures are investigated by impedance spectroscopy. The measurements were performed in the frequency and temperature ranges 20 Hz to 1 MHz and 150 K to 510 K, respectively. The composites exhibit strong low-frequency dispersion of electrical modulus and dielectric permittivity which is caused by different mechanisms of electron transfer at low and high temperatures. A hopping transport process with activation energy of 0.22 eV for exchange between Fe2+ and Fe3+ was tentatively assigned to reign below room temperature. It gradually changes to a conducting mechanism with activation energy of 0.45 eV above 345 K. [ABSTRACT FROM PUBLISHER]

Dielectric and noise characteristics of CoFe2O4-BaTiO3 ceramic composites were investigated. The complex dielectric permittivity displays a broad maximum around 300 K, where a phase transition occurs. The dielectric spectra of the complex dielectric permittivity are caused by the conductivity above 300 K. Intensive almost periodic telegraphic noise with relaxation type spectra is observed in the same temperature range (around 300 K). An investigation of the noise characteristic shows that several noise intensity peaks occur during this phase transition. [ABSTRACT FROM PUBLISHER]

New leadless ferroelectric relaxor 0.85Ag0.9Li0.1NbO3-0.15Bi0.5K0.5TiO3 ceramics have been obtained. The ceramics exhibits a smeared frequency-dependent maximum of permittivity, which follows the Fogel-Vulcher law with the freezing temperature T0 = 250 K. The Last mode in 0.85Al0.9Li0.1NbO3-0.15Bi0.5K0.5TiO3 ceramics is the ferroelectric soft mode inside polar nanoregions, with the critical temperature Tc = 437 K. [ABSTRACT FROM AUTHOR]

Quasistatic dielectric relaxation due to migration of charged point defects is considered as a mechanism of aging in ferroelectrics. A two-dimensional model is developed which includes the coupled potential problem and the field-driven diffusion problem. Numerical study reveals formation of space charge zones near the grain boundaries with the only characteristic time of several days being the Maxwell relaxation time defined by the charge carrier density and mobility. The clamping pressure due to charge segregation is about few MPa which corresponds to observed coercive stresses in perovskite ferroelectrics and is significantly stronger than in the mechanisms involving orientational reordering of defect dipoles. [ABSTRACT FROM AUTHOR]