Compression studies of TiB[subscript 2] using synchrotron x-ray diffraction

Abstract

The compressibility of TiB{sub 2} 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 TiB{sub 2} in this pressure range. The ultrasonic measurements of compressional V{sub p} and shear V{sub 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{sub To} = 232.9 {+-} 4.2 GPa and its pressure derivative K{sub 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{sub So} = 232.9 {+-} 1.6 GPa and K'{sub 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{sub So} = 259.8 {+-} 0.4 and G{sub So} = 2.52 {+-} 0.01, respectively.