Model concept on the role of structure-forming cations in self-assembling of molten crystallization media with ionic-covalent interactions

The aim of the paper is conceptual consideration of the role of structure-forming cations in self-assembly of molten crystallization media with ionic-covalent interactions and revealing the importance of these cations in structure transformations during melting (alloying) and crystallization of complex compounds. The proposed model concept is based on available experimental facts, crystal growth included, well-known scientific aspects, and formal-logical constructions. We assume that the key to understanding structural transformations of complex compounds is the need for large structure-forming cations to form a coordination sphere and charge compensation mechanism of system components adequate to phase state. Synthesis of specific associative complexes (AC) based on structure-forming cation inside polyanion sphere of particular configuration is assumed to be an imperative for the genesis of complex compound liquid state. In metastable state, AC and “free” structure-forming cations (not included in AC) undergo precrystallization self-assembling into evolutionary structuring clusters (quataron type). Inside these specific clusters AC easily transform into primary structure-forming modules of crystal lattice. The reasons of these phenomena, which are the essence of nucleation and crystallization processes, are discussed. The high-temperature phase of barium metaborate, α-BaB2O4 or BBO, was chosen as a model object for subject speculations.