Strength and equation of state of molybdenum triboride under 80 GPa pressure, using radial X-ray diffraction

ABSTRACTThe 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.