Single-crystal elasticity of SrCO3 by Brillouin spectroscopy

The elastic stiffness tensor c(ij) of synthetic strontianite (SrCO3) was determined by Brillouin spectroscopy at ambient conditions. An inversion procedure based on Christoffel's equation was used to determine the 9 independent elastic coefficients of orthorhombic strontianite from acoustic velocities measured along 69 different crystallographic directions in 3 randomly oriented crystal platelets. The best fit values of c(11), c(12), c(13), c(22), c(23), c(33), c(44), c(55) and c(66) are 153(1), 52(1), 38(11), 109.6(8), 43(15), 75(1), 28.0(5), 28.6(4) and 33.2(5) GPa, respectively. The linear compressibilities of a-, b- and c-axis at ambient conditions are 3(2), 4(6) and 10(8) 10(-3) GPa(-1). The adiabatic bulk modulus of strontianite is 64(4) GPa, intermediate between aragonite (CaCO3) and witherite (BaCO3), thus confirming a systematic linear relationship between cation radius and bulk modulus in aragonite-type carbonates. The shear modulus of strontianite has a value of 31(1) GPa, which is about 10% smaller in comparison to aragonite.