Phase transition regulation and piezoelectric performance optimization of fresnoite crystals for high-temperature acceleration sensing

Abstract

Fresnoite (Ba₂TiSi₂O₈ or BTS) crystals can be potentially used for high-temperature piezoelectric sensing because of their high electrical resistivity and strong piezoelectric response at elevated temperatures. However, anomalies in the electro–elastic properties due to phase transition limit the application of BTS crystals over a broad temperature range. In this study, strontium substitution crystals Ba_2−xSr_xTiSi₂O₈ (x = 0, 0.2, 0.4, and 0.6) were designed and grown using the Czochralski (Cz) pulling method. Phase transition was analyzed by in situ high temperature transmission electron microscopy, single-crystal X-ray diffraction and Brillouin light-scattering spectroscopy, where the observed acoustic anomalies exhibited softening of the longitudinal acoustic phonon mode, accounting for the phase transition of the BTS crystal. The bond valence sum was analyzed and Sr substitution was demonstrated to significantly improve the underbonding of the interlayer Ba cations. Phase transition was regulated and piezoelectric activity was optimized by Sr substitution. The results confirmed that Sr substitution could significantly increase the phase transition temperature and weaken the effect of phase transition on macroscopic electrical properties. Finally, a shear-mode prototype acceleration sensor with a stable sensing performance of up to 600 °C was fabricated.