Acoustic and electrical properties of Ca3Ta G a 3Si2O14 piezoelectric resonators at elevated temperatures

Synthetic piezoelectric crystals in the P321 crystal class have been a focus of substantial research in relation to their application in high-temperature resonant bulk-acoustic-wave (BAW) and surface-acoustic-wave (SAW) sensors. Most of this research has been on partially disordered langasite (LGS) and langatate (LGT), but fully ordered crystals in this class, such as Ca₃TaGa₃Si₂O₁₄ (CTGS), have been suggested as offering potentially superior performance. In this study, acoustic characteristics and electrical conductivity of CTGS bulk acoustic resonators with a crystal orientation of (YXl) -30° are investigated at the fundamental mode of 5 MHz and overtones of 15 MHz and 25 MHz in the temperature range from room temperature to 1100 °C. Magnitudes of the fractional changes in frequency with temperature are found to be less than 41 × 10^-6 K^-1 over this range, with turnover temperatures near 200 °C for the third and fifth overtones. The acoustic loss μ^-1 at ambient temperatures is greater than the lowest values previously reported for LGS and LGT. Between 100 °C and 700 °C, μ^-1 has two anelastic relaxation peaks that are similar to those previously reported for LGS and LGT. The electrical conductivity over the range from 500 °C to 1100 °C is found to be approximately an order of magnitude lower than that previously reported for LGS, and this leads to a reduction in μ^-1 at elevated temperatures.