Extension of the hcp-fccHe4Phase Diagram to about 9 kbar

The hcp-fcc transition in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ was investigated from 4 to 8.69 kbar by an optical method. The temperature hysteresis increases from 1 to 2.8 K, and the temperature width of the transition from 100 mK to about 2 K. The estimated equilibrium phase-transition line deviates increasingly with higher pressures from theoretical predictions.