Development and optimization of solid solution synthesis based on metal halides of two crystalline classes

The article presents a comprehensive approach to obtaining two classes of optical materials based on metal halides. The use of the thermozone crystallization–synthesis method is substantiated. This technology was applied to produce high-purity raw materials of two types: silver halides and complex silver-thallium halides. Optimal precursor compositions were selected to enable the preparation of raw materials with the desired composition while minimizing economic costs. Within the first class of materials, single crystal and ceramic samples with a composition of 20 mol. % AgI in AgCl 0.25 Br 0.75 were obtained. In the second class, samples of various structures based on 15 mol. % TlBr 0.46 I 0.54 in AgCl 0.25 Br 0.75 were produced. Optimal technological regimes for crystal growth and optical ceramic synthesis were determined. It was established that a single recrystallization cycle is sufficient to obtain ceramic samples. To grow single crystals, two or more recrystallization cycles are necessary to achieve maximum compositional homogeneity and solid solution supersaturation. Samples synthesized from the raw material, depending on the number of cycles, had different structures with identical chemical compositions. However, the structure inevitably affected the characteristics of each class of materials. For example, a significant reduction in transmittance was observed for optical ceramics due to the presence of alloying phase grains in the cubic matrix, despite similar microhardness values for samples of different structures. The study concluded that it is possible to obtain single crystals with high functional properties from the heterogeneous region of the melting diagrams of metal halides using thermozone crystallization synthesis.