Strength of polycrystalline niobium from high-pressure x-ray diffraction data: A comparison of results from line-width and line-shift analyses

Abstract

High purity polycrystalline niobium was compressed in a diamond anvil cell (DAC) without any pressure transmitting medium and the pressure was increased in steps of ∼5 GPa to the highest pressure of ∼40 GPa. The diffraction pattern was recorded after each pressure increment using angle-dispersive mode with the conventional diffraction geometry, wherein the primary x-ray beam is parallel to the load axis of the DAC. The strength of niobium as function of pressure was determined using the line-width and line-shift analyses. Both eY and 2eY, where Y is the aggregate Young's modulus and e is the strain determined from the line-width analysis, have been used as the measure of strength in earlier studies. In this study, it is eY that agrees with the strength determined from the line-shift analysis of the radial diffraction data as well as the data from the conventional diffraction geometry. These results have been discussed and compared with a similar observation made earlier on strength of diamond. This study highlights the ambiguity that presently exists in choosing eY or 2eY as a measure of strength while attempting to estimate the strength from the diffraction line width analysis.