Microstructural control of (Li, Na, K)NbO3 ceramics using additives

The microstructure of Li0.06Na0.52K0.42NbO3 piezoceramics was designed and controlled by the use of additives such as Li2CO3, SiO2, MnCO3, and SrZrO3. The electric and piezoelectric properties, microstructures, and compositional distribution of the additive elements are investigated in this paper. The average grain diameters decreased from 5.8 to 3.0 mu m when the following additives were incorporated: 0.65 mol% Li2CO3, 1.3 mol% SiO2, 0.2 mol% MnCO3, and 0.5 mol% SrZrO3. In addition, the maximum grain diameters decreased from 15 to 7.7 mu m. The compositional distributions were analyzed by energy dispersive X-ray spectrometry using a transmission electron microscope. Grains of SiO2 glass and the MnO compound were evaluated as diverse grains on the ceramic matrix. Because of the homogenization of the microstructure and the increased relative density, the resistivities were increased over the whole measuring temperature range. For example, the resistivities increased from 5.2 x 10(9) to 2.7 x 10(10) Omega.cm at 160 degrees C. The piezoelectric properties remained about the same: epsilon(T)(33)/epsilon(0) = 880, tan delta = 1.9%, k(r) = 41.8%, d(31) = -74 pC/N, and T-c = 470 degrees C. These results indicate an improvement in the reliability of structural refinement techniques for ceramics. (C) 2015 The Ceramic Society of Japan. All rights reserved.