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, GaAsO 4 , 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 SiO 2 = 8 % , k AlPO 4 = 11 % , and k GaPO 4 = 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 C 66 ′ 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 GaAsO 4 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 GaAsO 4 powder at high temperatures. It has been shown that GaAsO 4 is stable up to 1030°C. The thermal-expansion coefficient of GaAsO 4 is 4.0 × 10 − 5 K − 1 . The thermal expansion of the predicted AT plane ( Y − 6.3 ° ) in GaAsO 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 GaAsO 4 is the most stable in α -quartz materials, which enables one to predict that GaAsO 4 should retain high piezoelectric performances up to 925°C.