Thermal Expansion Coefficients for Solid Argon from 1 to 25 K

Measurements of the coefficient of linear thermal expansion accurate to 1% are reported for free-standing samples of solid argon for temperatures from 1 to 25 K. These data were obtained using a differential parallel-plate-capacitor technique and at low temperatures can be represented by $\ensuremath{\alpha}=(3.34{T}^{3}+0.030{T}^{5})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ ${\mathrm{K}}^{\ensuremath{-}1}$ ($1<T<6$ K). When combined with other data, these results can be used to obtain Gr\"uneisen parameters which are systematically 10% lower than those reported for anharmonic theories. Preliminary data also showed a low-temperature thermal expansion anomaly which is believed due to the spin-split ground state of ${\mathrm{O}}_{2}$ impurities.

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