Impact of high-temperature dielectric and piezoelectric behavior on LGT acoustic wave properties up to 900°C

The langatate (LGT) elastic, dielectric and piezoelectric constants with respective temperature coefficients up to 900°C are reported for the first time. The new set of constants was used to improve the predictions of high-temperature LGT surface acoustic wave (SAW) properties such as phase velocity (v_p), temperature coefficient of delay (TCD), and electromechanical coupling (K²) along multiple orientation sweeps up to 900°C. These predictions were then compared to previous calculations, which ignored the temperature dependence of the dielectric and piezoelectric constants, and to measured data up to 900°C, obtained from SAW delay lines fabricated along 6 orientations in the LGT plane (90°, 23°, Ψ). The average discrepancy between predicted and measured v_p and TCD responses between 25 and 900°C were reduced by a factor of 4 for vp and 13% for TCD when the temperature dependence of both dielectric and piezoelectric constants are considered. The extracted LGT piezoelectric constants and temperature coefficients show that e₁₁ and e₁₄ change by up to 62% and 77%, respectively, for the entire 25°C to 900°C range when compared to room temperature values. In addition, this paper uncovers the full set of high-temperature LGT elastic, piezoelectric, and dielectric constants and temperature coefficients applicable up to 900°C, including the respective estimated uncertainty.