Optical Constants of Triclinic Anisotropic Crystals: Blue Vitriol

摘要

In a recent paper we developed a method for determination of the complex dielectric tensor of triclinic crystals from experimental reflectance spectra. The somewhat simpler 2-D case represented by monoclinic anisotropic crystals provided a simpler problem on which to test our methodology. In this paper we wish to report on the reduction of our theoretical method for triclinic crystals to practice. The methodology is quite similar to that previously reported. The difficulty of the triclinic case principally resides in the expansion of the number of parameters that need to be simultaneously fit. We chose to use chalcanthite (CuSO4.5H20, commonly known as blue vitriol, as a relatively simple example of a triclinic crystal. The separation in frequency of the vibrations due principally to the sulfate anion and those due to water of crystallization was thought likely to be helpful in developing our technique. The principal complex refractive indices for blue vitriol (chalcanthite) have been derived in the infrared region of the spectrum. These values were obtained by dispersion analysis of the reflection spectra of a cube of chalcanthite taken with the electric vector at three orthogonal orientations involving two orthogonal arbitrarily oriented faces. This derivation of the optical constants in terms of the dispersion parameters, taking account of axis wander, demonstrates that it is now possible for any crystalline substance to be analyzed regardless of crystal system.