Lithium tris(oxalato)aluminate and its hydrates: structure, mutual transformations and thermal decomposition

Abstract

The double oxalates MI3[MIII(C2O4)3] possess rich crystallochemistry and can be used as precursors for various ceramic materials. The article discusses a case of Li3[Al(C2O4)3]. A series of previously unknown hydrates (Li3[Al(C2O4)3]·5.5H2O, Li3[Al(C2O4)3]·4H2O, Li3[Al(C2O4)3]·H2O) was found for this composition, their crystal structure and temperatures of mutual transformations determined. Transformation from Li3[Al(C2O4)3]·4H2O to Li3[Al(C2O4)3]·H2O was found to be accompanied by a change in the topology of the bonding network. Uniaxial negative thermal expansion was found for anhydrous Li3[Al(C2O4)3]. Thermal decomposition of Li3[Al(C2O4)3] was demonstrated to be a promising way to obtain precursors for aluminate ceramics.