Radial x-ray diffraction of tungsten tetraboride to 86 GPa under nonhydrostatic compression

Abstract

Investigations of the equation of state of tungsten tetraboride (WB4) have been performed under nonhydrostatic compression to 85.8 GPa using radial x-ray diffraction techniques in a diamond anvil cell at room temperature. The hexagonal structure of WB4 is found to be stable up to the highest pressure of 85.8 GPa. The radial x-ray diffraction data yield a bulk modulus K0 = 319(5) GPa with K0′ = 4.1(0.2) at ψ = 54.7°. With a fixed K0′ of 4, the derived K0 is 323(1) GPa. The bulk modulus obtained from fits of diffraction data at ψ = 0° and 90° is 196(6) GPa and 507(13) GPa, respectively. The values gradually increased from ψ = 0° to 90°, showing the compressibility of the sample strongly depends on the stress environment. In addition, the compressibility of the unit cell axes (a- and c-axes) of WB4 demonstrates an almost isotropic nature with pressure increasing.