The effect of crystallite size and stress condition on the equation of state of nanocrystalline MgO

Abstract

We performed high-pressure synchrotron x-ray diffraction experiments on nanocrystalline (nc-) MgO compressed both under quasi-hydrostatic and non-hydrostatic conditions in a diamond-anvil cell. Data obtained under hydrostatic conditions show that nc-MgO (average crystallite size of 20 nm) is 8-9% more compressible than "bulk" MgO. Analysis of our results collected under non-hydrostatic conditions yields a bulk modulus that is about 27% larger than the one derived from the quasi-hydrostatic compression experiments. Thus, the apparent bulk modulus strongly depends on the experimental stress conditions.

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

“…In comparison to previous studies (Andrault et al, ; Shieh et al, ; Singh et al, ), the small grain size of the here‐used sample might therefore enhance stresses between grains. When grain sizes get substantially smaller than in our polycrystalline stishovite sample, however, the elastic properties of grain boundaries themselves significantly contribute to the overall elastic response (Marquardt, Gleason, et al, ; Marquardt, Speziale, et al, ).…”

Compression of a multiphase mantle assemblage: Effects of undesirable stress and stress annealing on the iron spin state crossover in ferropericlase

“…Thus, in order to get reliable EOS parameters for multiphase materials, special attention must be paid in order to reveal their true compressional behavior. While our study is not the first in highlighting the manifestation of nonhydrostatic conditions or the effect of pressure medium deviation from hydrostaticity [ Marquardt et al ., ; Dorfman et al ., ; Anzellini et al ., ; Konôpková et al ., ], to the best of our knowledge, we are the first to highlight substantial complications in the case of multiphase materials (e.g., with phases welded one to another and/or with significant differences in elastic properties).…”

“…Following our discussion of F‐f E plots, by the annealing we produce a data point corresponding to the same volume or f E but at lower pressure. This is similar to what was observed in other studies [e.g., Marquardt et al ., ; Anzellini et al ., ].…”

“…This leads to pressure overestimation. Although, this effect was already covered in the literature [e.g., Marquardt et al ., ], we take a closer look at individual phases in a multiphase assemblage.…”

The equation of state of TaC0.99 by X-ray diffraction in radial scattering geometry to 32 GPa and 1073 K

“…The average for the studies using the generalized gradient approximation (GGA) is 315  16 GPa and overlaps with our result within reciprocal 1 uncertainties. One of the computational studies [33] [37] is based on a high-pressure X-ray diffraction study of nano-particle TaC, which could have a different elastic behavior with respect to the bulk material (see for instance the case of MgO [67]), and it has been fixed in the data analysis. The results of [32] are based on a similar approach as the one used in the present study and the large disagreement deserves a more detailed explanation.…”