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

Structural units of polycomponent melts modeled using diffraction, spectroscopy, and computation techniques

“…3e and f. This allows us to consider [Na 3 (B 3 O 6 ) 2 ] 3À complexes formed of two twisted (B 3 O 6 ) 3À groupings as integrated AC integ . 3 These complexes are actually dominating SU of the NaBO 2 melt as follows from the RDF data. The observed splitting of the second DM at 2.5-2.7 Å into two sub-DM at 2.2-2.3 and 2.8-3 Å upon overcooling suggests enhanced cation-anion interactions inside precursor clusters and formation of quasimolecular AC integ , i.e., with completely compensated charge (Fig.…”

“…However, only those AC will act as structure-forming units for nucleation and crystal growth, whose composition and arrangement dominate in the precrystallization state of the melt, including the state of cooperative interaction in precursor clusters of the potential crystal phase. 3 Polyatomic AC that are formed by fragments of anion polycondensate bound by structure-forming cations.…”

“…3b Spectroscopy of borate, silicate, and similar melts revealed that the polycondensed anion component is preserved but the ring groupings and infinite chains break during melting, which is evident from the Raman spectra ( Fig. 2c and d) [2,3]. The calculations of different configurations of AC with one complex-forming cation did not give good correlation of interatomic distances with the RDF data of NaBO 2 melt (Fig.…”

“…They differ from each other in the degree of ordering in their closest surrounding by oxygen atoms. According to our assumption discussed elsewhere [2,3], namely ''free'' cations (FC) that are outside of associative complexes and lack ordered surroundings by anions, provide self-assembling of CGU inside precursor clusters and a nucleation phenomenon through structural fluctuation.…”

“…Transformation of such AC to the crystal growth units with octahedral surrounding of cations, similar to that in the crystal structure of Na 2 SO 4 [5], requires a more active cooperative interaction of crystal-forming components. This type of interaction occurs in the precursor clusters of a quataron type [3], only under certain supercooling of the melt.…”