High-temperature langatate elastic constants and experimental validation up to 900°C

This paper reports on a set of langatate (LGT) elastic constants extracted from room temperature to 1100??C using resonant ultrasound spectroscopy techniques and an accompanying assessment of these constants at high temperature. The evaluation of the constants employed SAW device measurements from room temperature to 900??C along 6 different LGT wafer orientations. Langatate parallelepipeds and wafers were aligned, cut, ground, and polished, and acoustic wave devices were fabricated at the University of Maine facilities along specific orientations for elastic constant extraction and validation. SAW delay lines were fabricated on LGT wafers prepared at the University of Maine using 100-nm platinum rhodium- zirconia electrodes capable of withstanding temperatures up to 1000??C. The numerical predictions based on the resonant ultrasound spectroscopy high-temperature constants were compared with SAW phase velocity, fractional frequency variation, and temperature coefficients of delay extracted from SAW delay line frequency response measurements. In particular, the difference between measured and predicted fractional frequency variation is less than 2% over the 25??C to 900??C temperature range and within the calculated and measured discrepancies. Multiple temperature-compensated orientations at high temperature were predicted and verified in this paper: 4 of the measured orientations had turnover temperatures (temperature coefficient of delay = 0) between 200 and 420??C, and 2 had turnover temperatures below 100??C. In summary, this work reports on extracted high-temperature elastic constants for LGT up to 1100??C, confirmed the validity of those constants by high-temperature SAW device measurements up to 900??C, and predicted and identified temperature-compensated LGT orientations at high temperature.