High temperature piezoelectric properties of flux-grown α-GeO2 single crystal

Abstract

The temperature dependence of the piezoelectric properties of trigonal α-GeO2 single crystals obtained by the higherature flux method was measured by the resonance technique of the electrical impedance in the 20 °C-600 °C range. To approach the values of the two independent piezoelectric coefficients d11 and d14, we first measured as a function of temperature the elastic coefficients S11, S14, and S66 and the dielectric permittivity ϵ 11, which are involved in the coupling coefficient k of both the thickness shear mode and the transverse mode. A Y-cut plate with a simple +45° rotation [(YXtwl) +45°/0°/0°] was used to measure the coupling coefficient of the thickness shear mode, and two X-turned plates [(XYtwl) +45°/0°/0° and (XYtwl) -45°/0°/0°] were prepared to characterize the coupling coefficient of two transverse modes. From the whole experimental measurements, the piezoelectric coefficients of α-GeO2 were calculated up to 600 °C. They show that this crystal is one of the most efficient in regard to the α-quartz-like family at room temperature and that its thermal comportment retains large piezoelectric properties up to 600 °C.