Transition data and kinetics of the hcp-fccHe4transition between 4 and 9 kbar

The transition hcp-fcc ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ was studied from 4 to 9 kbar using an optical method. It was found that the estimated transition line is essentially linear in this range with a slope of 622 bar/K. This line deviates increasingly from theoretical predictions at higher pressures. The temperature hysteresis of the transition increases from 1 to 2.8 K, and the athermal width from 0.1 to 2 K. Detailed study of the kinetics near 9 kbar showed that both athermal and isothermal transformations are possible. The isothermal transformation goes to completion in heating, but not in cooling. Reproducibility of the $c$-axis orientation was also established for the athermal transition if prolonged annealing is avoided.