Nonhydrostatic compression of gold powder to 60 GPa in a diamond anvil cell: estimationof compressive strength from x-ray diffraction data

Abstract

Two gold powder samples, one with average crystallite size of≈30 nm (n-Au) andanother with ≈120 nm (c-Au), were compressed under nonhydrostatic conditions in a diamond anvil cell to different pressuresup to ≈60 GPa and the x-ray diffraction patterns recorded. The difference between the axial andradial stress components (a measure of the compressive strength) was estimated from theshifts of the diffraction lines. The maximum micro-stress in the crystallites (anothermeasure of the compressive strength) and grain size (crystallite size) were obtained fromanalysis of the line-width data. The strengths obtained by the two methods agreed well andincreased with increasing pressure. Over the entire pressure range, the strength of n-Au wasfound to be significantly higher than that of c-Au. The grain sizes of both n-Au and c-Audecreased under pressure. This decrease was much larger than expected from thecompressibility effect and was found to be reversible. An equation derived from thedislocation theory that predicts the dependence of strength on the grain size and theshear modulus was used to interpret the strength data. The strength derivedfrom the published grain size versus hardness data agreed well with the presentresults.