Microscopic scale evidence of phase transformation process in barium aluminosilicate glass-ceramic

The hexacelsian-celsian (H-M) phase transformation in barium aluminosilicate glass-ceramics (BAS) is sluggish. It is reported that Li⁺ dopants can promote this conversion effectively, but the detail reasons are still unclear. In this work, BAS glass-ceramics doped with different content of Li⁺ were synthesized by sol-gel method. Results suggest that Li⁺ dopant can accelerate the formation of hexacelsian at ∼800 °C and promote the phase separation between virgilite and BAS. Then the obtained hexacelsian phase starts to transform into celsian at 1300 °C and approximately completes at 1400 °C. During phase transformation process, the microstructure of hexacelsian-paracelsian, paracelsian-celsian and celsian coherent-phase were observed. It indicates that paracelsian serves as transient phase to reduce the difficulty of H-M phase conversion. This mechanism of hexacelsian-paracelsian-celsian (H-P-M) phase transformation gives the novel explanation of the effects of Li⁺ dopants on H-M phase transformation at microscopic scale.