Nonhydrostatic compression of bismuth to 222Â GPa: Some constraints on elasticity of the bcc-phase

Polycrystalline bismuth sample was compressed in a diamond anvil cell and X-ray diffraction patterns from the body centered cubic phase of bismuth (bcc-Bi) recorded in the pressure range 12-222 GPa. The analysis of diffraction data indicates that the factor S=(S11−S12−S44/2) is positive, where Sij are the single-crystal elastic compliances. The data suggest S/S11≅0.5 in the entire pressure range if stress continuity across the grain boundaries is assumed, and S/S11≅0.9 if a condition halfway between the stress and strain continuities is assumed. These results are compared with the first principle calculations of the elastic moduli carried out recently. The upper bound of the uniaxial stress component (the difference between the axial and radial stress components) increases linearly from very low value at 12 to ≈3 GPa at 222 GPa.