Linear Thermal Expansion of Lead‐Free Piezoelectric <scp> K _0.5 Na _0.5 NbO ₃ </scp> Ceramics in a Wide Temperature Range

Abstract

The objective of this work was to examine linear thermal expansion of K 0.5 Na 0.5 NbO 3 ceramics between room temperature and 790°C by contact dilatometry. The material was single phase with 95.5% relative density and with a uniform microstructure. Three distinct regions of thermal expansion could be discerned, corresponding to the three phases of K 0.5 Na 0.5 NbO 3 : monoclinic (assuming a single perovskite unit cell), tetragonal, and cubic, separated by discontinuities as typical for the first‐order phase transitions. The linear coefficient of thermal expansion between 30° and 195°C is 2.96 × 10 −6 K −1 , between 208° and 364°C is 4.35 × 10 −6 K −1 , and between 434° and 790°C is 7.52 × 10 −6 K −1 .