Compression studies of TiB2 using synchrotron x-ray diffraction and ultrasonic techniques -: art. no. 023506

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 65.9 GPa and 13.9 GPa, 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 2200 K at 40 GPa, indicating a phase stability of TiB2 in this pressure range. The ultrasonic measurements of compressional V-p and shear V-s 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 K-To=232.9+/-4.2 GPa and its pressure derivative K-To'=3.86+/-0.23. Similarly, the parameters derived from fitting the finite strain equation to the ultrasonic data give an adiabatic bulk modulus of K-So=232.9+/-1.6 GPa and K-So'=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 G(So)=259.8+/-0.4 and G(So)'=2.52+/-0.01, respectively. (C) 2005 American Institute of Physics.