Elastic Constants of Iron from 4.2 to 300°K

The zero-field elastic constants of iron have been measured from 4.2 to 300^∘{}K using the ultrasonic pulse technique. Extrapolation of the data to absolute zero gives c₁₁=2.431±0.008, c₁₂=1.381±0.004, and c₄₄=1.219±0.004, all expressed in units of 10¹² dyne cm^-2. The corresponding limiting value of the Debye temperature is θ₀=(477±2)^∘K. Using this figure, the low-temperature heat capacity data for iron have been reanalyzed assuming the presence of a spin-wave contribution to the specific heat, i.e., the heat capacity is assumed to follow the relation C=γT+βT³+αT3/2. A least squares fit of (C-βT³)T versus T1/2 gives γ=(11.7±0.1)×10^-4 cal mole^-1 deg^-2, α=(2±1)×10^-5 cal mole^- deg^-5/2. There is agreement, within experimental error, between the latter figure and the theoretical estimate of α=0.8×10^-5 cal mole^-1 deg^-5/2 obtained from the low-temperature magnetization data of Fallot. From the room temperature elastic constants, the compressibility of iron is found to be K=(5.95±0.02)×10^-13 cm² dyne^-1, which agrees exactly with the static value obtained by Bridgman.