PVTMeasurements of the hcp-bcc Phase Transition in SolidHe3

Abstract
The phase transition from hexagonal close-packed to body-centered cubic in solid He3 has been extensively investigated from 1 °K to the triple point using a sensitive method of measuring pressure versus temperature for constant volume samples. The triple point was found to be at 3.138°K and 135.44 atm. At 1 °K and 105.4 atm the phase boundary in the PT plane is practically horizontal. Using previous data for the molar volume of the solid along the melting curve, the phase diagram in the VT plane has been constructed. From the change in volume at the transition and the slope dPdT, the change in entropy was calculated using the Clapeyron equation. Measurements in the hcp phase below 1.5°K near the phase boundary were complicated by supercooling, making it difficult to obtain equilibrium in this region.

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