Dielectric Nonlinearity and the Velocity of Ultrasonics in the Region of the Structural Phase Transition in (K0.5Na0.5)(Nb1 – xTax)O3 Ceramics

Properties of the dielectric response of (K 0.5 Na 0.5 )(Nb 1 – x Ta x )O 3 + 0.5 mol % MnO 2 (KNN- x Ta) ferroelectric ceramics at temperatures including that of the structural phase transition (SPT) from the orthorhombic phase to tetragonal is studied and compared to the behavior of elastic properties in this region of temperatures. The character is determined of the concentration dependences of such anomalies as the temperature of the maximum of permittivity T max ( x ) in the SPT region and temperature T extr at which the maximum increment of permittivity upon specimen heating in the SPT region occurs. It is found temperature T extr coincides with the one at which minimum v ( T ) of the velocity of a longitudinal acoustic wave is observed at SPT. Features of a nonlinear dielectric response associated with the coexistence of different types of domain boundaries in the region of a smeared structural transition in KNN- x Ta ceramics are determined in studying the temperature behavior of polarization loops.