Single-crystal elasticity of stishovite: New experimental data obtained using high-frequency resonant ultrasound spectroscopy and a Gingham check structure model

Single-crystal elasticity of stishovite was examined using a new experimental technique and an empirical macroscopic model. Employing high-frequency resonant ultrasound spectroscopy, single-crystal elastic constants of stishovite were determined: C ₁₁=443(3), C ₃₃=781(4), C ₁₂=193(2), C ₂₃=199(2), C ₄₄=256(2), and C ₃₃=316(2)GPa. The frequency range of the resonant ultrasound spectroscopy techniques was 6-20MHz, which is much lower than the ~10GHz range of the Brillouin scattering technique. Of the elastic constants, the shear elastic constants C ₄₄ and C ₆₆ are consistent with the average value of the previously mentioned Brillouin scattering. Conversely, the four elastic constants, C ₁₁, C ₃₃, C ₁₂, and C ₂₃, slightly deviate outside the range of previous Brillouin scattering results. The present results, except those for C ₁₂, are consistent with recent lattice dynamic analysis of inelastic X-ray scattering data. The adiabatic bulk modulus was calculated as 298GPa, which is smaller and more consistent with the result of compression experiments than any other Brillouin scattering results (301-312GPa). The present result shows greater P-wave velocity anisotropy (24.7%) than any preceding work. To understand the unique elastic properties of stishovite, the Gingham check model was proposed and examined. The result shows that the octahedron of 6-coordinated Si in stishovite crystal has stiffness comparable to that of diamond.