The leucite group structures are tetrahedrally coordinated silicate framework structures with some of the silicate framework cations partially replaced by divalent or trivalent cations. These structures have general formulae A2BSi5O12 and ACSi2O6, where A is a monovalent alkali metal cation, B is a divalent cation, and C is a trivalent cation. These leucites can have crystal structures in several different space groups, dependent on stoichiometry, synthesis conditions, and temperature. Phase transitions are known for temperature changes. This paper reports a high-temperature X-ray powder diffraction study on RbGaSi2O6, which shows a phase transition from I41/a tetragonal to Ia-3d bar on top of 3 cubic on heating from room temperature to 733 K. On cooling to room temperature, the crystal structure reverts to I41/a tetragonal.

Leucites are tetrahedrally coordinated silicate framework structures with some of the silicon framework cations partially replaced by divalent or trivalent cations. These structures have general formulae A2BSi5O12 and ACSi2O6; where A is a monovalent alkali metal cation, B is a divalent cation, and C is a trivalent cation. In this paper, we report the Rietveld refinements of three more synthetic leucite analogues with stoichiometries of Cs2NiSi5O12, RbGaSi2O6, and CsGaSi2O6. Cs2NiSi5O12 is Ia$\bar{3}$d cubic and is isostructural with Cs2CuSi5O12. RbGaSi2O6 is I41/a tetragonal and is isostructural with KGaSi2O6. CsGaSi2O6 is $I\bar{4}3d$ cubic and is isostructural with RbBSi2O6.