ELASTIC PROPERTIES OF SILICA POLYMORPHS – A REVIEW

The elastic properties of silica phases are reviewed. Available monocrystal data for crystalline SiO2 polymorphs (low-quartz, high-quartz, low-cristobalite, high-cristobalite, stishovite) are collected from the literature, and effective elastic constants (Young's moduli, shear moduli, bulk moduli and Poisson ratios) are calculated from these using Voigt-Reuss-Hill averaging. Both experimental data and simulation results are taken into account. A table of room temperature elastic constants for crystalline silica polymorphs and silica glass is given that lists the recommended current "state-of-the-art" values. All data are consistent with the well-known auxetic behavior of cristobalite at room temperature, and high-temperature simulation data published for cristobalite confirm auxetic behavior for all temperatures from room temperature up to more than 1500°C. The calculations of this paper show that also quartz can be auxetic, but only in a very limited temperature range around the low-to-high-quartz transition temperature (420 - 577°C). Experimental measurements of elastic properties of tridymite and cristobalite, including high-temperature measurements, are identified as a desideratum of future research.