High temperature piezoelectric properties of flux-grown α-GeO 2 single crystal

International audienceThe temperature-dependence of the piezoelectric properties of trigonal -GeO2 single-crystals obtained by the high-temperature 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 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 -GeO2 were calculated up to 600 °C. They show that this crystal is one of the most efficient in regard of the -quartz-like family at room temperature, and that its thermal comportment retains large piezoelectric properties up to 600°C

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Elasticity and anelasticity of oxide glasses

0031-9090International audienceThe current understanding of sound properties in glasses is reviewed and compared to that in crystals. Sound damping in oxide glasses is controlled mainly by three processes which in increasing order of the frequency at which they dominate are: the thermal relaxation of defects, relaxation via anharmonic interactions with the thermal bath, and hybridization with optic-like vibrations. The former two also affect distinctly the velocity of sound. The latter one relates to the boson peak and the low temperature plateau generally observed in the thermal conductivity. In addition, in silica and other tetrahedrally coordinated glasses, the sound velocity tends to increase with temperature, presumably owing to a progressive structural change