High temperature electromechanical behaviour of sodium substituted lithium niobate ceramics

Abstract

Complex impedance spectroscopy measurements in air were carried out as a function of the temperature on poled samples of sodium substituted lithium niobate ceramics, Li _1-x Na_xNbO ₃3 (LNN), with Na contents of 7, 10, 15, 18 and 25 mol%. An NaNbO ₃-rich phase is segregated, which greatly influences the thermal behaviour of the ferro-piezoelectric properties of the ceramics. The results of the measurements at the thickness resonance of thin disks, poled at 180°C with fields of 80 to 100kV/cm, show that all the samples have piezoelectric activity up to temperatures of 800°C or above. An automatic iterative procedure was used to obtain the values of some relevant piezoelectric, elastic and dielectric complex coefficients as a function of the temperature.