Single-crystal elasticity of the rhodochrosite at high pressure by Brillouin scattering spectroscopy

The sound velocity properties of single-crystal rhodochrosite (MnCO₃) were determined up to 9.7 GPa at ambient temperature by Brillouin scattering spectroscopy. Six elastic constants were calculated by a genetic algorithm method using the Christoffel's equations at each pressure. The elastic constants increased linearly as a function of pressure and its pressure derivatives ∂Cij/∂P for C₁₁, C₃₃, C₄₄, C₁₂, C₁₃, C₁₄ were 5.86 (±0.36), 3.82 (±0.44), 2.06 (±0.39), 5.07 (±0.27), 5.34 (±0.44), 1.52 (±0.24), respectively. Based on the derived elastic constants of rhodochrosite, the aggregate adiabatic bulk and shear moduli (K_s and G) were calculated using the Voigt-Reuss-Hill averages and the linear fitting coefficients (∂K_s/∂P)_T and (∂G/∂P)_T were 5.05(±0.26) and 0.73(±0.05), respectively. The aggregate V_p of rhodochrosite increased clearly as a function of pressure and its pressure derivative ∂V_p/∂P was 7.99(±0.53) × 10⁻² km/(s GPa), while the aggregate V_s increased slowly and ∂V_s/∂P was only 1.19(±0.12) × 10⁻² km/(s GPa). The anisotropy factor for As of rhodochrosite increased from ∼40% at 0.8 GPa to ∼48% at 9.7 GPa, while A_p decreased from ∼19% to ∼16% at the corresponding pressure.