Modular structures inherited from high-temperature disordered parent ones

[Marco E. Ciriotti]

Prossima pubblicazione.

Referenza:
▪ Shablinskii, A., Filatov, S.K., Biryukov, Y. (2023): Modular structures inherited from high-temperature disordered parent ones: an example of Ca2SiO4, Na2SO4–K2SO4 sulfates and related minerals. Preprint.

Abstract:
Crystal structures of Ca2SiO4, Na2SO4–K2SO4 sulfates and related minerals bubnovaite K2Na8Ca(SO4)6 and dobrovolskyite Na4Ca(SO4)3 were described as modular ones for the first time. A microblock, or a module[M(TO4)6] that is consisted of an octahedron interlinked by six vertices with six adjacent tetrahedra was considered as a structural unit inherited upon cooling from a high-temperature disordered parent one. A relationship between the parent and inherited microblocks was established. As a result, fifteen possible types of modules maintaining a trigonal symmetry of the microblocks were derived based on this relationship. It was shown, that the minerals and compounds structurally-related with α-Na2SO4 derived superstructures were formed as a result of a cooling of the high-temperature phases containing the disordered parent microblock. Here, a driving force of the inheritance is a tendency of the structure to order upon cooling. The reasons of a formation of a microblock from the parent one are mainly determined by ionic radius and type of a cation occupying the octahedral site. A finding of minerals with the described structural features could be a promising tool for a synthesis of novel compounds with useful properties.