The book describes and analyzes the available theoretical and experimental material on the solubility and crystallization of insoluble metal halides in various solvents using the example of solid solutions Ag. Hal and Tl. Hal. Thermodynamic studies of silver and monovalent thallium halide systems are presented, including new Ag. diagrams Br TlI and Ag. Br (Tl. Br0.46. I0.54), by methods of X-ray phase and differential-thermal analysis. The method of growing crystals of stoichiometric composition based on solid solutions of metal halides is described by the authors , as well as the results of the variation in composition and alloying elements , which made it possible to obtain a wide range of volumetric crystals with various physical and optical properties, designed to operate in the spectral range from 0, 4 to 45, 0 m. The book is intended for undergraduates, graduate students, and process engineers. The work was carried out with the financial support of the Government of the Russian Federation, Resolution No. 211, Contract No. 02. A03. 21. 0006.