Compression studies of TiB2 using synchrotron x-ray diffraction and ultrasonic techniques

The compressibility of TiB2 has been determined separately by synchrotron x-ray diffraction and ultrasonic measurements on samples loaded in diamond-anvil cells and in multianvil high-pressure apparatus up to pressures of 65.9GPa and 13.9GPa, respectively, at ambient temperature. The high-pressure x-ray diffraction measurements, carried out on a pure polycrystalline sample, show a monotonic decrease of the lattice parameters with pressure, with the c∕a ratio variation suggesting an increase in the structural rigidity along the c direction. No structural transition is observed even after laser heating of the sample up to 2200K at 40GPa, indicating a phase stability of TiB2 in this pressure range. The ultrasonic measurements of compressional Vp and shear Vs velocities on a cylindrical specimen show linear pressure dependencies. Using the third-order Eulerian finite strain equation to fit the pressure-volume x-ray data, we obtain an isothermal bulk modulus of KTo=232.9±4.2GPa and its pressure derivative KTo′=3.86±0.23. Similarly, the parameters derived from fitting the finite strain equation to the ultrasonic data give an adiabatic bulk modulus of KSo=232.9±1.6GPa and KSo′=3.02±0.24, in good agreement with the x-ray diffraction measurements. The shear modulus and its pressure derivative derived from the ultrasonic measurements are GSo=259.8±0.4 and GSo′=2.52±0.01, respectively.