Acoustic and electrical properties of Ca3TaGa3Si2O14 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 degrees 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 degrees C. Magnitudes of the fractional changes in frequency with temperature are found to be less than 41x10(-6) K-1 over this range, with turnover temperatures near 200 degrees C for the third and fifth overtones. The acoustic loss Q(-1) at ambient temperatures is greater than the lowest values previously reported for LGS and LGT. Between 100 degrees C and 700 degrees C, Q(-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 degrees C to 1100 degrees C is found to be approximately an order of magnitude lower than that previously reported for LGS, and this leads to a reduction in. Q(-1) at elevated temperatures.