Piezoelectric characterization and thermal stability of a high-performance α-quartz-type material, gallium arsenate

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 (k_SiO2=8%, k_AlPO4=11%, and k_GaPO4=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^-5 K^-1. The thermal expansion of the predicted AT plane (Y-6.3°) in GaAsO<- inf>4 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.