Elasticity and rheology of platinum under high pressure and nonhydrostatic stress

Using radial x-ray diffraction under nonhydrostatic compression in a diamond-anvil cell, we determine a lower bound of the yield strength of polycrystalline platinum to be 2. 2 to 3. 3 GPa in the pressure range of 4. 2 to 22. 4 GPa at room temperature. The elastic anisotropy S=2 (S₁₁-S₁₂) /S₄₄ of platinum is also evaluated, and is equal to 1. 47 (16) throughout this pressure range. In addition, platinum shows a time-dependent relaxation under nonhydrostatic stress at both ambient temperatures and, in a separate set of experiments, during laser heating. Average strain rates measured for platinum are 10^-7s^-1 at 300 K and 10^-5s^-1 at 1200 K, resulting in effective creep viscosities of 10^15Pas at 300 K and 10^13Pas at 1200 (300) K.