Processing, Characterization, and Dielectric Studies on K(Ta1−xNbx)O3 for Use at Cryogenic Temperatures

Abstract

Development of the next generation space telescope, to supplement the Hubble Space Telescope, has heightened the need for cryogenic actuators. High performance electromechanical materials are needed for use from 10 to 77 K. The use of piezoelectric materials to satisfy this need involves major property trade‐offs; consequently, alternative materials are of interest—the electrostrictive ceramics. The electrostrictors operate above their “Curie” (transition) temperature, and have electromechanical properties that can be superior to conventional piezoelectric materials. Because work on the electrostrictive materials is limited, the K(Ta,Nb)O3 solid solution system has been chosen as a viable material for use at cryogenic temperatures. These solid solutions have predicted transition temperatures in the range of 4 to 150 K. Two separate KTaO3 powders were synthesized with 10 and 17.5 mol% Nb2O5 doping levels. The powders were synthesized via a conventional mixed oxide route and materials were fabricated using a tape cast and laminating technique. Powders and samples were characterized using laser scattering, scanning electron microscopy, and surface area analysis to determine particle size distribution and morphology, powder X‐ray diffractometry for phase composition, and dielectric response as a function of frequency and temperature. Tape casting and lamination produced final samples that were fabricated to ∼88% of theoretical density. Dielectric measurements resulted in Curie temperatures of 248 and 123 K, and weak‐field permittivity values of ∼2700 and 4000 for 17.5 and 10 mol% additions of Nb2O5 to KTaO3.