Determination of the Pressure of the Barium I-II Transition with Single-Stage Piston-Cylinder Apparatus

The pressure of the barium I-II transition has been determined in a modified single-stage piston-cylinder apparatus to be 55.0±0.5 kbar at 22°C. Three barium samples of different purity were used and no significant variation of the transition pressure found. The temperature coefficient of the transition pressure is 0–0.015 kbar/°C near room temperature. The effect of the presence of dissolved hydrogen on the transition pressure is discussed.