Elastic, dielectric and piezoelectric properties of a EuCa4O(BO3)3 high-temperature piezoelectric crystal

The rare-earth oxyborate crystal RCa₄O(BO₃)₃ (RCOB, R: rare-earth elements) is an inorganic photoelectric multifunctional material, which has important applications in the field of high-temperature piezoelectricity. In this work, a EuCa₄O(BO₃)₃ (EuCOB) crystal with a diameter of 25 mm was successfully grown by the Bridgman method. The thermal conductivity, thermal diffusivity and specific heat of the EuCOB crystal at high temperature were measured. The dielectric coefficient, electromechanical coupling coefficient, elastic coefficient and piezoelectric coefficient of the EuCOB crystal at high temperature were measured by the resonance–antiresonance method. In particular, the shear piezoelectric coefficient d₂₆ of the EuCOB crystal is 7.01 pC N⁻¹ at room temperature and 6.22 pC N⁻¹ at 800 °C, with a small variation of 11.4%. The electrical resistivities of the EuCOB crystal along the X, Y and Z directions at 800 °C are 5.8 × 10⁷ Ω cm, 3.1 × 10⁷ Ω cm and 2.9 × 10⁷ Ω cm, respectively. The large piezoelectric coefficient and high electrical resistivity indicate the potential application of the EuCOB crystal in a high-temperature piezoelectric field.