Linear-thermal-expansion measurements on potassium metal from 2 to 320 K

A differential capacitance dilatometer has been used to obtain linear-thermal-expansion measurements on free-standing samples of high-purity potassium metal from 2 to 320 K. The low-temperature results are consistent with a free-electron calculation of the electronic contribution to the thermal-expansion coefficient, while the lattice contribution can be represented by a Gr\"uneisen parameter γ which varies slowly with temperature from approximately 0.90 at T=0 to 1.24 near the melting point, in agreement with γ's as calculated from high-pressure elastic-constant data. Slight inconsistencies (1% or so) were found for temperatures between 20 and 30 K, and between 100 and 200 K, which are believed to be traceable to the thermal history of the samples. A summary of existing bulk-modulus data is given for use with the γ calculations. The data are normalized to published bulk-density measurements at 300 K, and the resulting $T=0$ molar volume (43.21 ±{} 0.02 cm³/mole) can be used with the free-electron model to calculate a de Haas-van Alphen frequency which is in excellent agreement with direct determinations. When the smoothed linear-thermal-expansion coefficients are used to calculate CVˡᵃᵗ(T) from published results for Cₚ(T), anharmonic effects (CV proportional to T) are evident above 100 K, while vacancy effects become important above 250 K.