Acoustic phonons and elastic stiffnesses from Brillouin scattering of CdPS3

Abstract

We report Brillouin light scattering measurements of monoclinic CdPS3, a 2D layered cadmium chalcogenophosphate. By measurement of over 400 spectra in different orientations and scattering geometries, acoustic phonons are measured to determine the 13 elastic stiffness coefficients, along with longitudinal and transverse sound velocities from Brillouin frequency shifts. Because the sample was polycrystalline with a high density of planar defects, it was not possible to assign a crystal orientation to each spectrum. Instead, we determined the anisotropy in the material properties through statistical analysis, treating each spectrum as coming from a randomly sampled crystal orientation. Values of the Voigt–Reuss averages for the bulk modulus, Young’s modulus, the shear modulus, and Poisson’s ratio are calculated from measured stiffnesses. This work demonstrates analysis of elastic properties of a polycrystalline, monoclinic 2D layered material through statistical analysis of a significant number of spectra.