Thermal expansion of solid parahydrogen at helium temperatures

Thermal expansion of solid parahydrogen is investigated in the temperature range from 0.9 to 5 K. The content of the orthomodification in parahydrogen is 0.13 at. %, and that of nonhydrogen impurities is less than 2·10−3 at. %. No anisotropy in thermal expansion was observed within the experimental error. The temperature dependence of the linear expansion coefficient can be described by the expression α = 1.82·10−7 T3. The obtained values of a are in good agreement with the available data on compressibility and (∂p/∂T)T. The Grüneisen coefficient is γ = 3αV/CTχT = 2.00±0.25.

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