Verres aux halogenures de cadmium : I.- Verres fluores

New halide glasses based on cadmium halides as glass progenitors have been discovered. This paper describes fluoride glasses in the CdF₂-BaF₂-ZnF₂ ternary system. Binary glasses Cd_xBa_1?xF₂ (0.45 < x < 0.52) have been obtained. The limits of the glassy area are: 5–55 % CdF₂, 15–55 % BaF₂, 0–60 % ZnF₂. Numerous fluorides such as the alkali fluorides, AlF₃, YbF₃ and ThF₄ may be included in the glass composition. Only thin glass samples may be prepared because of the high crystallization rate. The characteristic temperatures of the Cd_0.3Ba_0.4Zn_0.3F₂ glass are 290° C for T_G, 330° C for T_C and 620° C for T_F. The optical transmission spectrum of a thin sample shows an extrinsic absorption band at around 9000 nm and the multiphonon IR absorption edge beyond 10500 nm. The optimization of these glasses will make them attractive materials for IR transmittance and IR optical fibres. The crystallization of the Cd_0.5Ba_0.5F₂ glass results in two solid solutions Ba_1?xCd_xF₂ and Cd_1?xBa_xF₂ deriving from the fluorite structural type. Thus, cadmium fluoride glasses appear as the result of the disordering of the fluorite type structure in the same way as ZrF₄-based glasses derive from the disordering of the ReO₃-type structure. Both glasses may be described as the random insertion of cations into an aperiodic array of F^? anions.