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

The temperature dependence of the piezoelectric properties of trigonal alpha-GeO2 single crystals obtained by the high-temperature flux method was measured by the resonance technique of the electrical impedance in the 20 degrees C-600 degrees C range. To approach the values of the two independent piezoelectric coefficients d(11) and d(14), we first measured as a function of temperature the elastic coefficients S-11, S-14, and S-66 and the dielectric permittivity epsilon(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 degrees rotation [(YXtwl) +45 degrees/0 degrees/0 degrees] was used to measure the coupling coefficient of the thickness shear mode, and two X-turned plates [(XYtwl) +45 degrees/0 degrees/0 degrees and (XYtwl) -45 degrees/0 degrees/0 degrees] were prepared to characterize the coupling coefficient of two transverse modes. From the whole experimental measurements, the piezoelectric coefficients of alpha-GeO2 were calculated up to 600 degrees C. They show that this crystal is one of the most efficient in regard to the alpha-quartz-like family at room temperature and that its thermal comportment retains large piezoelectric properties up to 600 degrees C. Published under license by AIP Publishing.