High temperature piezoelectric response of polycrystalline Li-doped (K,Na)NbO3 ceramics under compressive stress

Abstract

The influence of uniaxial compressive stress on small-signal relative permittivity and direct piezoelectric coefficient of polycrystalline Li-modified (K0.5Na0.5)NbO3 (0, 2, and 4 mol. % Li) was characterized as a function of temperature from 25 to 450 °C. These data reveal corresponding anomalies in both the dielectric and piezoelectric properties near the well-known structural phase transitions in (KxNa1-x)NbO3. In particular, increasing stress was found to shift the orthorhombic-tetragonal (T O-T) and tetragonal-cubic (T C) phase boundaries to higher temperatures, thereby stabilizing the lower symmetry phases. Experimental results also show that stress up to a critical value flattens the piezoelectric response below T O-T, above which a monotonic decrease is observed. In contrast, permittivity is increased below T O-T with increasing stress. These results are used to construct a stress-temperature phase diagram of Li-modified (K0.5Na0.5)NbO3