Elasticity of coesite

The single-crystal elastic constants of SiO2, coesite (monoclinic, C2/c), have been determined from Brillouin scattering measurements on a 100-μm crystal. The elastic constants inferred from acoustic velocities for 80 different propagation directions are (in units of Mbar) c11 = 1.608, c22 = 2.304, c33 = 2.316, c44 = 0.678, c55 = 0.733, c66 = 0.588, c12 = 0.821, c13 = 1.029, c15 = −0.362, c23 = 0.356, c25 = 0.026, c35 = −0.393, and c46 = 0.099. This experimental technique provides a method of determining single-crystal elastic properties for materials such as high-pressure phases that are not available in sufficiently large sizes for ultrasonic measurements.