Lithium germanates: Synthesis, crystal-chemical analysis and their structural invariants

Abstract

The crystal-chemical classification of Li-germanates was performed. Depending on the types of Ge-polyhedra and their interconnections, the Li-gennanates ace divided into 3 groups: the framework MT-structures; the MT condensed structures and T-structures. The structure invariant M₂T₄ is established in the framework germanates and in Li₄Ge₃ ^VI Ge₃ ^VIO₁₂ germanate with M, T condensed structure. The crystals synthesized is in hydrothermal GeO₂—LiOH—H₂O system are analyzed on the basis of crystal-chemical classification suggested. The representatives of all groups mentioned above are formed in aqua solutions at high temperatures and pressures. The most stable germanate is characterized b the direct condensation of the dimmers M₂T₄. Germanates with a prevalence of Ge in the structure (M₃T₂ and MT₃) exist in a very small region at low kmperatures and low LiOH concentration, then they are replaced by the framework germanate MT₂.

Key Words:

• Lithium germanates
• Hydrothermal synthesis
• Single crystals
• Crystal-chemistry
• Classification
• Structure invariant