Intrinsic birefringence of a chiral sodium chlorate crystal: Is cubic crystal truly optically neutral?

We have for the first time observed birefringence of a chiral cubic crystal of class T, along the [1 0 0] directions, and proved that the anisotropy is of an intrinsic nature. The measurement of artifact-free linear birefringence (LB) and circular birefringence (CB = optical rotatory dispersion (ORD)) was made possible by the use of our universal chiroptical spectrophotometer (UCS) which was developed especially for solid-state samples [R. Kuroda, T. Harada, Y. Shindo, Rev. Sci. Instrum. 72 (2001) 3802; T. Harada, R.Kuroda, Chem. Lett. 3 (2002) 326]. A set of procedures for obtaining artifact-free LB was also devised in this study based on the Mueller matrix method. Only the non-birefringent axis is along the [1 1 1] directions.