Measurement and analysis of nonhydrostatic lattice strain component in niobium to 145 GPa under various fluid pressure-transmitting media

The d spacings in niobium have been measured to 145 GPa with a diamond anvil cell using a fluid13; pressure-transmitting medium methanolx2013;ethanolx2013;water MEW mixture, or helium. The13; conventional geometry, wherein the primary x-ray beam passes parallel to the load axis with image13; plate, has been used to record the diffraction patterns. The analysis of the d spacings using the lattice13; strain equations indicates the presence of nonhydrostatic stress component with both MEW and He13; pressure-transmitting media in the pressure ranges that are well below the freezing pressure of the13; pressure-transmitting medium. A method to correct the measured d spacings for the nonhydrostatic13; pressure effect is suggested. This study clearly emphasizes the need to carefully analyze the data for13; the nonhydrostatic compression effects even if the experiments are performed with fluid13; pressure-transmitting medium