Temperature Variation of Elastic Properties of α- Quartz up to the α-β Transition

Abstract

The temperature variations of normal mode frequencies of a specimen of α-quartz single-crystal have been measured nearly up to the α-β transition (T₀ 573°C), and all of the independent elastic constants were determined simultaneously by the rectangular parallelepiped resonance method. The results demonstrate that bulk moduli decrease largely toward T₀, while shear moduli show only a slight decrease. The trigonal constant C₁₄ decreases just below T₀, but seems to remain a finite value even at T₀. It is noted that the isotropic aggregate of α-quartz is a curious and scarce material in the sense that its bulk modulus is smaller than the shear modulus, and Poisson's ratio is very small or even negative at temperatures higher than 450°C. In the measured temperature variations of mode frequencies, a characteristic feature was observed when two branches of A_g modes came close, suggesting mode coupling. Except for this coupling between A_g modes themselves, no definite evidence was observed which was indicative of coupling between modes of different symmetry. So it can be said the present sample is uniform in its property enough to suppress the coupling between modes of different symmetry.