Phase transitions and dielectric properties of (1-x)KNbO3 - xK(0.5)Bi(0.5)TiO(3) ceramics synthesized by a stirred hydrothermal process

Dielectric ceramic materials (1 - x) KNbO3 - xK(0.5)Bi(0.5)TiO(3) (0 <= x <= 0.3) have been successfully synthesized via a stirred (dynamic) hydrothermal method. The microstructure, relative density and dielectric properties were studied as a function of KBT doping. The structure of the solid solutions changed from orthorhombic (x = 0; 0.05) to tetragonal (x = 0.1; x = 0.3) at room temperature. The morphotropic phase limit was obtained at x = 0.075 where we have noted the coexistence of the orthorhombic and tetragonal structures. The mean value of the measured dielectric permittivity epsilon(r) was 700 and dielectric loss tan delta was about 0.06 at room temperature. The dielectric properties of the studied ceramics, from 80 to 450 K, depend not only on their microstructure but also on their relative density. A relaxation behavior was observed for the tan delta curves at temperature below 150 K. The activation energy (E-a) of this phenomenon increases from 0.15 to 0.34 eV with the increase of KBT amount. The conductivity sigma(ac) remains constant at about 10(-6) S m(-1). (C) 2015 Elsevier B.V. All rights reserved.