Piezoelectric Properties near the Tricritical Point on KF-Doped BaTiO₃Single Crystal

Abstract

The temperature dependence of the piezoelectric constant d33, electromechanical coupling factor k33, dielectric constant ε33T and elastic compliance s33E for a single crystal of KF-doped barium titanate with a KF content near the tricritical point (TCP), Ba0.91K0.09TiO2.91F0.09 (KF-BT/0.09), was measured by a resonance–antiresonance method in a temperature range between 270 and 340 K. The single crystals used were grown by a KF-flux method and the largest single crystal was a cube of 5 mm size. A large piezoelectric constant and a large dielectric constant were obtained at 300 K: d33 = 300 pC/N, k33 = 0.59, and ε33T = 3,000. As the temperature increases, ε33T gradually increases toward TC but does not show any discontinuous changes at TC = 329 K; moreover, s33E and d33 increase with temperature between 270 and 310 K. However, above 310 K, they decrease toward TC. The fluctuation of the order parameter near the TCP induces these peculiar behaviors.