Elasticity of α-Cristobalite: A Silicon Dioxide with a Negative Poisson's Ratio

Abstract

Laser Brillouin spectroscopy was used to determine the adiabatic single-crystal elastic stiffness coefficients of silicon dioxide (SiO₂) in the α-cristobalite structure. This SiO₂ polymorph, unlike other silicas and silicates, exhibits a negative Poisson's ratio; α-cristobalite contracts laterally when compressed and expands laterally when stretched. Tensorial analysis of the elastic coefficients shows that Poisson's ratio reaches a maximum value of –0.5 in some directions, whereas averaged values for the single-phased aggregate yield a Poisson's ratio of –0.16.