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The structural, dielectric, ferroelectric and piezoelectric properties of 0.90[x(Bi1/2 Na1/2)TiO3-(1-x)(Bi1/2K1/2)TiO3]-0.10(Bi1/2Ag1/2)TiO3 (BNKA) ceramics were studied for the compositional range, x = 0.73-0.89. The morphotropic phase boundary (MPB) composition of the system appears to be near BNKA-79 according to the results of the X-ray diffraction. The optimal piezoelectric properties are observed in the MPB region. The sample with x = 0.79 showed the highest piezoelectric constant d33 = 160 pC/N. The maximum electromechanical coupling factors, kp and kt, are 0.30 for BNKA-79 and 0.42 for BNKA-85, respectively. [ABSTRACT FROM AUTHOR]

Dielectric and impedance spectroscopies were employed to study intergrowth Bi5TiNbWO15 ferroelectrics. It was observed one ferroelectric phase transition at 1096 K and two dielectric relaxation processes involving bulk and grain boundary effects. It was also found that the bulk response within the material is of localized relaxation process, the temperature dependence of the relaxation strength is analogous to the Curie-Weiss law and the interactions between the oxygen vacancies in the bulk material follow the traditional point defects relaxation theory. Based on the analysis of the crystal structure, a short range diffusion mechanism of oxygen ions coordinating A sites was proposed. [ABSTRACT FROM AUTHOR]