Determination of the elastic constants of β-Carbon monoxide by Brillouin spectroscopy

Abstract

Brillouin spectroscopy has been used to determine the adiabatic elastic constants for the hexagonal close-packed (β) phase of solid carbon monoxide near the triple point. In units of 10⁹ N/M², the elastic constants were found to be: -- c₁₁ = 1.909 -- c₁₂ = 1.151 -- c₁₃ = .955 -- c₃₃ = 2.104 -- c₄₄ = .356 -- Each of the above values is subject to an uncertainty of about 4%. However, most of this error is included in a multiplicative factor common to all five elastic constants, and uncertainties of less than 1% remain if this factor is divided out. The elastic constants were calculated from experimental data consisting of 35 Brillouin spectra showing various combinations of the longitudinal and the first and second transverse Brillouin components. The spectra were obtained by using a triple-pass Fabry-Perot interferometer to analyze laser light scattered by a single crystal of β-carbon monoxide with a known orientation. The crystal orientations were established from Laue x-ray diffraction photographs, and a fully algebraic procedure for interpreting the photographs has been developed and described in considerable detail. Derived elastic properties, in particular, bulk modulus, linear compressibility, and Young's modulus, have been calculated for β-CO and the values have been compared with those of four other materials having hexagonal crystal symmetry. A high degree of similarity was observed when comparing the elastic properties of β-CO with those of β-N₂.