Mineral-like Synthetic Compounds Stabilized under Hydrothermal Conditions: X-ray Diffraction Study and Comparative Crystal Chemistry

Abstract

Under hydrothermal conditions emulating natural hydrothermalites, three oxo-salts with sodium and transition metal cations were obtained in the form of single crystals. Their compositions and crystal structures were studied using scanning electron microscopy, microprobe X-ray spectral analysis, and X-ray single-crystal diffraction. The sodium cobalt silicate, i.e., Na2CoSiO4, a structural analog of the mineral liberite, is well known as an ionic conductor. Its crystal structure consists of a framework derived from β-tridymite, built using the Co- and Si-centered tetrahedra sharing vertices. The sodium oxocuprate phosphate chloride Na2Cu3O(Cu0.8Na0.2)(PO4)2Cl belongs to a group of compounds, including fumarolic minerals, characterized by the presence of oxo-centered pyroxene-like chains in their structures. The crystal structure of mineralogically probable sodium vanadium phosphate hydroxide (Na3V(OH)(HPO4)(PO4)) is based on chains built using octahedra centered by magnetically active V3+. Magnetic susceptibility measurements indicate an antiferromagnetic arrangement of V3+ ions and no transition to an ordered state up to 2 K.