Peculiar Structural Effects in Pure and Doped Functional Single Crystals of Complex Compositions

Results of a detailed structural characterization of nominally pure and doped single crystals of scheelite, eulytin, and perovskite families obtained by melt methods were considered and analyzed. The influence of growth and post-growth annealing conditions on actual compositions of crystals is shown. The reasons for the coloration of the crystals are explained. A change in crystal symmetry due to crystal–chemical and growth reasons is considered. The use of structural analysis and X-ray absorption spectroscopy is substantiated to reveal the role of activator ions in the formation of statistical and local structures, respectively. A relationship between the distribution of activator ions over crystallographic sites and photoluminescent parameters of materials is established, which allows selecting optimal systems for the application. The combined results of studying single-crystal compounds of other classes (huntite, sillenite, whitlockite, garnet, tetragonal bronzes) allow formulating and summarizing structural effects that appeared in the systems and caused by various factors and, in many cases, due to the local environment of cations. A principal difference in the structural behavior of solid solutions and doped compounds is shown. The methodology developed for single-crystal samples of complex compositions can be recommended for the systematic structural studies of functional materials of different compositions.