Strength and equation of state of molybdenum triboride under 80 GPa pressure, using radial X-ray diffraction
The strength and equation of state of molybdenum triboride have been determined under nonhydrostatic compression up to 80 GPa, using an angle-dispersive radial X-ray diffraction technique in a diamond anvil cell (DAC). The RXD data yield a bulk modulus and its pressure derivative as K0 = 342(6) GPa with K0‧ = 2.11(17) at ψ = 54.7°. Analysis of diffraction data using the strain theory indicates that the ratio of differential stress to shear modulus (t/G) ranges from 0.002 to 0.050 at pressures of 4-80 GPa. Together with theoretical results on the high pressure shear modulus, our results here show that molybdenum triboride sample under uniaxial compression can support a differential stress of ∼10 GPa when it started to yield with plastic deformation at ∼30 GPa. In addition, we draw a conclusion that MoB3 is not a superhard material but a hard material.