Mechanism of structural phase transitions in the Li4GeO4-ZnGeO4 system: Computer modeling and identification of invariant nanocluster structures in Li4GeO4, LISICON Li6Zn(GeO4)2, and Li4Zn2(GeO4)2 (γ phase)

The cluster modeling of structural phase transitions Li4GeO4 → LISICON Li6Zn(GeO4)2 → γ-Li4Zn2(GeO4)2 was carried out using computer-assisted methods (the TOPOS program package). The precursor nanoclusters of crystal structures were recognized in an automated data processing mode using an algorithm developed for selecting combinations from nonintersecting suprapolyhedral clusters. 3D macro-structure modeling employed the principle of maximal space filling and, accordingly, took into account the requirement for the maximal complementary connectivity of precursor nanoclusters in crystal structure self-assembly followed by consecutive primary chain-microlayer-microframework assembly. A crystallochemically correct structure model was advanced for superionic LISICON Li6Zn(GeO4)2 as a 2D analogue of Li4GeO4 containing only two types of voids in a layer, which are most likely to be sites for Li atoms to reside. A migration map was constructed to characterize the 2D set of conductivity channels in superionic LISICON.