Heat Capacity and Other Properties of Body-Centered CubicHe4

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Abstract
The heat capacity at constant volume, Cv, of bcc He4 has been measured for a number of molar volumes covering most of the bcc region of the phase diagram. The results can be represented to within 3% of Cv by a constant Debye Θ of 16.95°K. Using the discontinuities in the heat capacity at the phase boundaries measured in this and in previous work, the compressibility κ is found to be (3.8±0.2)×10−3 atm−1 and substantially independent of temperature, while values of the expansion coefficient α found by the same method are between 5×10−3 and 13×10−3 deg−1. The values of α are consistent with a Gruneisen equation with a Gruneisen constant γ≈2.6, the value found previously for hcp He4. The latent heats at constant volume at the lower and upper triple points T1 and T2 have been measured as a function of volume and give for the maximum entropy change at T1, where (hcp+liq) → (bcc), the value ΔS1R=(9±1)×10−3. The maximum entropy change at T2, where bcc → (hcp+liq), has the value ΔS2R=(32±2)×10−3. The triple-point temperatures were found to be T1=1.463±0.002°K and T2=1.7715±0.001°K. The intersection of the λ line with the bcc phase boundary has been confirmed to be ∼10 mdeg below the upper triple point. The entropy of the bcc phase at the transition line has been computed from the heat-capacity results and the latent-heat measurements, and is found to vary from SR=0.037±0.002 at T1 to SR=0.068±0.003 at T2. The relation between S and

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