Structural phase transition, strength, and texture in vanadium at high pressure under nonhydrostatic compression

The structural phase transition, strength, and texture of vanadium have been studied under nonhydrostatic compression up to 70 GPa using an angle-dispersive radial x-ray diffraction technique in a 2-fold paranomic diamond anvil cell and up to 38 GPa using an angle-dispersive x-ray diffraction technique in a modified Mao-Bell diamond anvil cell at room temperature. We have confirmed a phase transition from body-centered cubic structure to rhombohedral structure at 27-32 GPa under nonhydrostatic compression. The radial x-ray diffraction data yields a bulk modulus K₀=141(5) GPa and its pressure derivative K'₀=5.4(7) for the bcc phase and K₀=154(13) GPa with K'₀=3.8(3) for the rhombohedral phase at ψ=54.7°. The nonhydrostatic x-ray diffraction data of both bcc and rhombohedral phases yields a bulk modulus K₀=188(5) GPa with K'₀=2.1(3). Combined with the independent constraints on the high-pressure shear modulus, it is found that the vanadium sample can support a differential stress of ~1.6 GPa when it starts to yield with plastic deformation at ~36 GPa. A maximum differential stress as high as ~1.7 GPa can be supported by vanadium at the pressure of ~47 GPa. In addition, we have investigated the texture up to 70 GPa using the software package MAUD. It is convinced that the body-centered cubic to rhombohedral phase transition and plastic deformation due to stress under high pressures are responsible for the development of texture.