The optical dispersion in the organic-inorganic bis-dodecylammonium zinc tetrachloride (${\mathrm{C}}_{12}$${\mathrm{H}}_{25}$${\mathrm{NH}}_3$${)}_2$${\mathrm{ZnCl}}_4$ crystal [in short, BAA(12)-${\mathrm{ZnCl}}_4$] around its isotropic point was investigated by means of birefringence and optical-absorption measurements. The birefringence dispersion data are analyzed with use of a simple oscillator model based on the optical band structure of BAA(12)-${\mathrm{ZnCl}}_4$. The adjustable parameters used for the theoretical birefringence are related with the oscillator strength and average position, respectively. The thermal behavior of the involved parameters is in accordance with the optical-absorption data obtained from the temperature dependence of the absorption edge. These results suggest the existence of a structural phase transition at 315 K.

• Received 29 June 1987

DOI:https://doi.org/10.1103/PhysRevB.37.1814