Ultrahigh-temperature piezoelectric crystal ErxGd1−xCa4O(BO3)3 with near-zero temperature-shift of piezoelectric properties

To meet the sensing demands of extreme environments, such as those encountered in aircraft engines and nuclear industries, there is an urgent need to develop new piezoelectric crystals with excellent stability in piezoelectric performance. In this study, rare-earth mixed Er x Gd 1− x Ca 4 O(BO 3 ) 3 (Er x Gd 1− x COB, x = 0.30, 0.40, and 0.45) crystals were grown via the Czochralski method, and the electro-elastic properties were characterized over the temperature range of −100 °C to 900 °C. The results demonstrated that the Er 0.45 Gd 0.55 COB crystal exhibited exceptional temperature stability across the entire temperature range, with a negligible variation of only −3% in the piezoelectric coefficient d 26 . The fatigue behaviors of the electrical resistivity and piezoelectric coefficient were further investigated at 850 °C for 100 h. The results indicated that the electrical resistivity of Er 0.45 Gd 0.55 COB crystal remained within the same order of magnitude, approximately 8 × 10 7 Ω·cm, whereas the piezoelectric coefficient d 26 decreased only slightly by −4.2%. Furthermore, a prototype piezoelectric vibration sensor with an average sensitivity of 0.75 pC/g was fabricated using the Er 0.45 Gd 0.55 COB crystal, and the sensor exhibited a negligible sensitivity variation of ∼4% over the temperature range of 25 °C–800 °C. These results demonstrate the strong potential of Er x Gd 1− x COB crystals for high-temperature piezoelectric sensing applications.