Effects of Alkali Cations and Sulfate/Chloride Anions on the Flux Growth of {001}-Faceted β-Li₂TiO₃ Crystals

The β-Li₂TiO₃ crystal is an important material in several energy-related applications, and the control of its morphology and exposed facets is an important issue. Herein, we comprehensively studied the flux growth of β-Li₂TiO₃ crystals under different conditions and demonstrated the efficient anisotropic growth of {001}-faceted β-Li₂TiO₃ single crystals from the Na₂SO₄ flux. By examining the effects of the cation and anion in the alkali metal salt-based flux, we found that Na₂SO₄ flux is best for growing large, faceted β-Li₂TiO₃ crystals. In this flux at 1000 °C, the optimal solute concentration is 20 mol % for growing large (∼15.0 μm in lateral size), platy, and faceted β-Li₂TiO₃ crystals. Observations from varying the holding time and cooling rate indicated that these crystals were anisotropically grown. Transmission electron microscopy images with clear electron diffraction spots revealed that the flux-grown platy β-Li₂TiO₃ crystals are single crystalline solids with the {001} plane being the dominant facet. This anisotropic crystal growth could be attributed to the concerted effects of the preferential attachment of sodium cations on the {001} faces, and efficient dissolution of β-Li₂TiO₃ crystals as well as the solvation of the resulting O^2- ions in the sulfate anion-based flux.