Diamond’s elastic stiffnesses from 322 K to 10 K

Using resonant-ultrasound spectroscopy, we measured diamond’s monocrystal elastic-stiffness coefficients C11, C12, and C44, between 322 and 10 K. Changes are small and smooth: The bulk modulus B=(C11+2C12)/3 increases about 1 part in 1000, describable by a quasiharmonic Einstein-oscillator model. Zero-temperature Cij correspond to a 2244-K Debye characteristic temperature. Using a low-temperature form of the Grüneisen–Debye model, we calculated an overall thermodynamic Grüneisen parameter of γ=1.26; using a high-temperature form we calculated 0.71; the lattice specific heat yields γ=1.10.