ThirdOrder Elastic Coefficients of Crystals
Abstract
IT is well known that the number of independent secondorder elastic coefficients required to describe the behaviour of cubic crystals is three, irrespective of the class to which they belong, whereas the corresponding number for isotropic bodies is two. That a crystal of the cubic system differs from an isotropic body in another important respect, namely, its photoelastic behaviour, was discovered by Pockels. Pockels, however, as in the case of elasticity, made no distinction between the five classes of crystals coming under the cubic system, but assigned three coefficients only for all of them. Contrary to this., one of us^{1} showed, by a different method based on group theory, that the T and T_{h} classes of the cubic system require four coefficients for the description of their photoelastic behaviour, whereas the other three classes T_{d}, O and O_{h} require only three. This prediction has been verified by us experimentally by working with crystals of potassium alum^{2}.
 Publication:

Nature
 Pub Date:
 November 1947
 DOI:
 10.1038/160750b0
 Bibcode:
 1947Natur.160..750B