Simultaneous ultrasonic and synchrotron x-ray studies on pressure induced α-ω Phase transition in zirconium

Compressional and shear wave velocities as well as unit-cell volumes across the α-ω transition of Zr have been measured up to 10.5 GPa at room temperature using ultrasonic interferometry in conjunction with synchrotron x radiation. In the pressure range of 5.0 to 6.2 GPa, a mixture of α and ω phase is clearly identified and the α phase is completely transformed to ω phase at 6.8 GPa. The measured velocity jumps across the α-ω transition are 9.6% and 13.1% for P and S waves, respectively. Negative pressure dependence for the shear modulus of α-Zr has been found at pressures from 1.4 to 2.9 GPa, which may be ascribed to the shear instability of the α phase prior to transition. According to velocity data, the onset pressure of the α-ω transition is determined to be ∼4.0 GPa.