Elastic Constants of Galena

Abstract

RECENTLY, Ramachandran and Wooster1 have obtained the elastic constants of galena, among other substances, from measurements on diffuse reflexion of X-rays, and reported disagreement with the values given earlier by one of us2. Ramachandran has also directed our attention to this in private communications. This substance, in the light of such values, also figures as an exception in a paper by Lonsdale3 dealing with the vibration amplitudes of atoms in cubic crystals. Its elastic constants have therefore been re-determined, employing the wedge method and a very much better crystal than was available at the time of the earlier investigations. Frequencies in the range 2–12 Mc./sec., and (001) and (111) sections of different thicknesses ranging from 1.450 mm. to 1.929 mm., have been used. Constants now obtained along with the bulk modulus K in units of 1011 dynes cm.−2 are c11 = 12.70, c12 = 2.98, c44 = 2.48 and K = 6.22. They show that the Cauchy relation is fairly well satisfied. c44 and c12 do not differ very much from those of Ramachandran and Wooster, whereas c11 is somewhat larger. These values are to be regarded as much more reliable than any published earlier.