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The phase transition temperatures and piezoelectric properties of (Bi0.5Na0.5)TiO3 (BNT) ceramics and single crystal were investigated. This study revealed that the high conductivity of BNT ceramics is attributed to the Bi vaporization during sinterint. The highest depolarization temperature Td of 187°C was obtained for the stoichiometric BNT ceramics, and Td tends to decrease as the composition deviates from stoichiometric BNT. Td of BNT single crystal was 158°C because of Na poor composition. BNT ceramics was easy to pole fully when the Bi/Na ratio is more than 1.0. The electromechanical coupling factor k33 and piezoelectric properties d33 of fully poled stoichiometric BNT ceramics were 0.459 and 72.9 pC/N, respectively. [ABSTRACT FROM AUTHOR]

Aging of Na0.5 + xBi0.5 - xTiO3 - x (x = 0, 0.02) ceramics is studied by dielectric measurements. The time dependence of the dielectric property is well fitted by the stretched exponential function. The observed aging temperature dependences are different between Na0.52Bi0.48TiO2.98 and Na0.5Bi0.5TiO3 in relation with the concentration of oxygen vacancies. The aging temperature dependences of the relaxation intensity and the relaxation time in Na0.52Bi0.48TiO2.98 (which contains more oxygen vacancies) is consistent with the result of Monte-Carlo simulation which is based on the relaxation of defect dipoles in relaxor ferroelectrics. It is found that the oxygen vacancies are mainly responsible for the defect dipole. The aging behavior can be explained on the basis of the size of defect-dipole and its distribution. [ABSTRACT FROM AUTHOR]