Measurement of high-temperature resonant acoustic loss of piezoelectric crystals with noncontacting transduction

Piezoelectric crystals in the P321 crystal class (“langasite family”) can serve as a basis for resonant acoustic sensors that operate at temperatures exceeding the range of conventional piezoelectric resonators, but their performance can be limited by high-temperature acoustic loss Q −1, including point-defect anelasticity and conductivity-related loss. Accurate characterization of sources of loss in research studies aimed at optimizing performance are challenging, partly due to external damping from conventional deposited electrodes and leads. This talk describes an implementation of a resonance technique for measurements of Q −1 of piezoelectric crystal disks in vacuum at elevated temperatures with noncontacting transduction and continuously ramped temperature. The system includes crystal support on three sapphire spheres, noncontacting electrodes, and direct piezoelectric excitation with a tone burst applied across these electrodes. Data on Q −1 of catangasite from 300 to 925 °C and 4.5 to 22.4 MHz are presented and fit to a superposition of two anelastic relaxations, constant contact-related loss, and broad temperature-dependent background, which is assumed to arise from structural defects. From this analysis, point-defect relaxations are found to be the dominant contributions to Q −1 over the measured range, and contact-related loss is two orders of magnitude smaller than the minimum measured Q −1.