No abstract

Piezoelectric measurements were performed on large single crystals (8 mm along the c direction) of an α-quartz-type piezoelectric material, gallium arsenate, GaAsO4, which allow us to extend the structure-property relationships in the α-quartz-type materials. These first measurements on Y-rotated-cut plates have shown that gallium arsenate is the highest-performance piezoelectric material of this group. As compared to the coupling coefficients of the other materials with the same structure (kSiO2=8%, kAlPO4=11%, and kGaPO4=16%), gallium arsenate exhibits the highest piezoelectric coupling coefficient of about 22%, as has been predicted by the structure-property relationships. Moreover, from these piezoelectric measurements, the C66′ elastic constant was determined and compared with elastic constants in quartz-type materials. The proposed value for the cut angle of the AT plane in GaAsO4 is −6.3°. In order to extend the previous thermal stability results, thermal gravimetric analysis (TGA) and x-ray diffraction have been carried out on GaAsO4 powder at high temperatures. It has been shown that GaAsO4 is stable up to 1030 °C. The thermal-expansion coefficient of GaAsO4 is 4.0×10−5K−1. The thermal expansion of the predicted AT plane (Y−6.3°) in GaAsO4 is shown to be similar to that of the other materials. Finally, it is demonstrated that the intertetrahedral bridging angle θ (A–O–B) of GaAsO4 is the most stable in α-quartz materials, which enables one to predict that GaAsO4 should retain high piezoelectric performances up to 925 °C.

We calculated the lattice dynamics, the second-order nonlinear susceptibility, and the electro-optic response of the germanium dioxide in its αquartz-type form (α-GeO 2 ) from first-principles calculations based on density functional theory. No theoretical or experimental investigations of these nonlinear optical properties have been previously reported in the literature. The calculation of the infrared and Raman spectra of α-GeO 2 allowed us to assign its experimental phonon modes, contributing to the clarification of a long-standing debate in the literature. The second-order nonlinear susceptibility and the electro-optic coefficients of α-GeO 2 are predicted to be significantly higher than those reported for α-quartz. Thus, α-GeO 2 should be a promissing candidate for nonlinear optical applications when compared to α-quartz.