Measurements of Lattice Constant, Thermal Expansion, and Isothermal Compressibility of Neon Single Crystals

Single crystals of 99.995% purity neon were grown by directional solidification from the liquid, and the x-ray lattice constant was measured by means of a rotating-camera method. The volume coefficient of thermal expansion was determined over the interval 2.5 to 23.9°K with a precision ranging from 5 ppm °${\mathrm{K}}^{-1\mathrm{}}$ at low temperatures to 18 ppm °${\mathrm{K}}^{-1\mathrm{}}$ at the highest temperature. The lattice constant extrapolated to 0°K is 4.46368±0.00009 Å*. Lattice-constant measurements of a crystal under hydrostatic helium pressure gave values of the isothermal compressibility over the temperature range 4.2 to 20.6°K. The compressibility extrapolated to 0°K is (0.89±0.02) × ${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^2$ ${\mathrm{dyn}}^{-1\mathrm{}}$. This result is compared with the predicted values of several theoretical models. The isothermal compressibility and the volume coefficient of thermal expansion are combined with the heat capacity at constant pressure to determine the temperature variation of the thermal Grüneisen parameter and the caloric Debye characteristic temperature. Existing theoretical treatments of the lattice dynamics of neon appear to be inadequate at finite temperatures.