Hydrostatic compression and high-pressure elastic constants of coesite silica

Abstract

Using density-functional theory, we computed all the independent elastic constants of coesite, a high-pressure polymorph of silica, as functions of pressure up to 15 GPa. The results are in good agreement with experimental measurements under ambient conditions. Also, the predicted pressure-dependent elastic properties are consistent with x-ray data in the literature concerning lattice strains at high pressures. We find that coesite, like quartz, exhibits a gradual softening of a shear modulus B 44 with increasing pressure, in contrast to the rising bulk modulus. CommentsCopyright 2008 Using density-functional theory, we computed all the independent elastic constants of coesite, a high-pressure polymorph of silica, as functions of pressure up to 15 GPa. The results are in good agreement with experimental measurements under ambient conditions. Also, the predicted pressure-dependent elastic properties are consistent with x-ray data in the literature concerning lattice strains at high pressures. We find that coesite, like quartz, exhibits a gradual softening of a shear modulus B 44 with increasing pressure, in contrast to the rising bulk modulus.

Hardness of polycrystalline SiO2 coesite

“…Results of sound velocity measurements are summarized in Table . The present compressional ( V P ) and shear ( V S ) velocities as well as derived bulk ( K ) and shear ( G ) moduli show reasonable agreements with results of previous studies . Using the obtained K and G , we calculated Young's modulus and Poisson's ratio to be 148.8(7) and 0.24(3) GPa, respectively.…”

Tracking silica in Earth's upper mantle using new sound velocity data for coesite to 5.8 GPa and 1073 K

“…The P wave velocity increases with increasing pressure at all temperatures, while the S wave velocity decreases continuously along all isotherms from 300 K to 1073 K. These velocity-pressure data are consistent with the results at room temperature from our previous study [Chen et al, 2015] and further confirm that the velocity-pressure behavior observed at room temperature is preserved at high temperatures. Such shear wave softening feature agrees with the decrease of shear elastic constant C 44 from density functional calculations [Kimizuka et al, 2008].…”

“…Recently, anomalous elastic behavior has also been found by our acoustic study at high pressures but room temperature [ Chen et al , ]: unlike most mantle minerals (e.g., olivine and diopside), the shear wave velocity of coesite decreases with increasing pressure in the experimental pressure range up to 12.6 GPa. This is consistent with the predicted softening of C 44 under pressure from density‐functional theory calculations [ Kimizuka et al , ], which might indicate a precursor to amorphization or phase transitions with further pressure increase [e.g., Černok et al , ; Hemley , ].…”

First-principles elastic properties ofα-Pu

“…22 More recently the elastic constants of coesite, a monoclinic high-pressure polymorph of silica, were calculated 23 and these compared favorably with experimental data. Another low-symmetry system, ␣-U ͑a closer neighbor to Pu͒, has been investigated within DFT and the obtained elastic properties agree well between various computations 13,24,25 and measured data.…”

“…In our case we use the Murnaghan form 26 for this purpose, and the results are presented in Table I. On the other hand, B can be evaluated from the elastic compliance constants s ij ͑tabularized in Table IV͒, which are components of the inverse to the elastic-constant matrix, 23 B −1 = s 11 + s 22 + s 33 + 2͑s 12 + s 13 + s 23 ͒. ͑1͒…”