Auxetic properties of silicon dioxide single crystals

A systematic study of the effect of anomalous deformations and anisotropy of elastic properties on the formation of auxetic properties of stable (α- and β-quartz, α- and β-cristobalite) and metastable (coesite and stishovite) silicon dioxide single crystals was carried out. The characteristic surfaces of Young's moduli, angular distributions of Poisson's ratios and indicating auxeticity surfaces of the above single crystals were constructed. It was found that there is an unambiguous correlation between the anisotropy parameters of the characteristic surfaces of Young’s moduli and the auxeticity of single crystals. It is shown that when approaching the points of phase transformation of α- and β-quartz (TΦ = 846 K), α- and β-cristobalite (TΦ = 1050 K) the auxeticity degree Sa = 1.0, and the extreme values of Poisson's ratios μmin and μmax take negative values and single crystals become absolute auxetics.