type: Hooke

references:
  - R.A. Ayres et al.,
    Journal of Applied Physics 46:1526-1530, 1975,
    https://doi.org/10.1063/1.321804,
    fit to Table IV (T_min=100K, T_max=300K)

C_11: 524.6e+9
C_11,T: -5.783e+07
C_11,T^2: -1.355e+05

C_12: 219.0e+9
C_12,T: 1.940e+07
C_12,T^2: 7.634e+04

C_44: 168.7e+9
C_44,T: -2.048e+07
C_44,T^2: -5.478e+04

T_ref: 293.15