Diamond anvil cell measurement of high-pressure yield strength of vanadium using in situ thickness determination

The pressure dependence of the quasistatic yield strength of vanadium in polycrystalline foils and powders has been measured up to 90 GPa at room temperature using an implementation of a nonhydrostatic diamond-anvil cell technique, an extension of the technique of Meade and Jeanloz [C. Meade and R. Jeanloz, J. Geophys. Res. 93, 3261 (1988)]. A feature present in this work is the use of an in situ determination of the sample thickness and pressure profile using synchrotron x-ray techniques, allowing a determination of the strength at each point across the sample. Following an initial increase in the strength with pressure, a decrease in the strength of vanadium was observed starting at {approx}40-50 GPa. The softening of the yield strength of vanadium at high pressure is quite surprising and unusual, following the trend of an unusual softening of the shear modulus associated with a subtle phase transition from body-centered-cubic-to-rhombohedral structure in a recent x-ray diffraction experiment.