type: Hooke

references:
  - W.C. Overton, Jr. and J. Gaffney,
    Physical Review 98(4):969-977, 1955,
    https://doi.org/10.1103/PhysRev.98.969,
    fit to Tab. I (T_min=100K, T_max=300K)

C_11: 168.6e+9
C_11,T: -3.779e+7
C_11,T^2: -2.536e+4

C_12: 121.5e+9
C_12,T: -1.632e+7
C_12,T^2: -1.116e+4

C_44: 75.59e+9
C_44,T: -2.912e+7
C_44,T^2: -1.669e+4

T_ref: 293.15