Compression behavior of TaC0.98 under nonhydrostatic and quasi-hydrostatic pressures up to 76Â GPa

Powder samples of TaC0.98 sandwiched between aluminum disks were placed in a rhenium gasket and compressed in a diamond anvil cell. The X-ray diffraction patterns were recorded under pressures up to 50 GPa using synchrotron radiation. The presence of aluminum in the cell rendered the sample pressure nearly hydrostatic and also served as the pressure standard. In another set experiments, TaC0.98 powder mixed with small quantity of platinum powder was placed in stainless steel gasket and compressed between the anvils. The X-ray diffraction patterns were recorded up to 76 GPa. In absence of any pressure-transmitting medium, the stress state of the sample was expected to be highly nonhydrostatic. The diffraction data were analyzed using lattice strain theory to estimate t, the difference between the axial and radial stress components in the sample. The magnitudes of t suggest that the lower limit of compressive strength of TaC0.98 increases with increasing pressure and reaches ∼11 GPa at 76 GPa pressure. No phase transformation was observed up to the highest pressure. The bulk modulus and its pressure derivative derived from the volume-compression-pressure data are 345(9) GPa and 4.0(4), respectively.