Phase stability and structure of alkali doped-beta-gallia rutile intergrowths

The incorporation of alkali cations into the tunneled structure of Ga4TiO8 was investigated and compared to predictions based on atomistic computer simulations. Samples were prepared as AxGa4−xTi1−xO8, A=Li, Na, and K, x ≤ 0.7, and as NaxGa4+xTi2−xO10 (x = 0.7, 0.85, and 1.0) using solid-state reactions at 1050–1350 °C. The sodium-containing tunneled structure, NaxGa4−xTi1−xO8, formed via solid-state reaction, but the potassium and lithium analogs did not. Instead, these systems formed mixed-phase assemblages, which are discussed in reference to compatibility triangles in the Li2O–Ga2O3–TiO2 and K2O–Ga2O3–TiO2 systems. Experimental results were compared to the results of energy minimization calculations using the General Utility Lattice Program (GULP). For the lithium-containing system, the computer simulations correctly predicted the formation of a mixed-phase assemblage containing LiGa5O8, Ga2O3, and TiO2. For the sodium- and potassium-containing system, the computer simulations suggested that mixtures of the single-cation oxide components should be the stable phase assemblages, in contradiction with experimentally observed results. Energy minimization calculations conducted on structurally different NaxGa4+xTi2−xO10 and NaxGa4+xTi3−xO12 phases indicated that those based on the n = 6 and n = 7 β-gallia rutile intergrowth structures have lower lattice energies than the experimentally observed sodium titanogallate structures reported previously in literature.