Strength of polycrystalline coarse-grained platinum to 330 GPa and of nanocrystalline platinum to 70 GPa from high-pressure x-ray diffraction data

X-ray diffraction patterns from platinum foil 300 nm grain size have been recorded up to 330 GPa using a beveled-anvil diamond cell. The compressive strength has been determined from the analysis of the diffraction linewidths. In a separate set of experiments, coarse-grained platinum powder 300 nm grain size is compressed up to 64 GPa in a diamond anvil cell with 300 m flat-face anvils and diffraction patterns are recorded. The strengths as functions of pressure derived in the two sets of experiments agree well. The strength increases linearly from 0.21 2 GPa at zero pressure to 9.8 4 GPa at a pressure of 330 GPa. The nanocrystalline platinum sample 20 nm average grain size exhibits much higher strength and increases linearly from 3.0 1 to 8.0 3 GPa as the pressure is increased from zero pressure to 70 GPa. The grain size of nanocrystalline sample decreases with increasing pressure. The effect of nonhydrostatic compression on the pressures determined with platinum as a pressure marker in high-pressure x-ray diffraction studies is discussed