Preparation and phase transition of Gd₄(Al_1-xGa_x)₂O₉ solid solutions

The solid-solution compounds of Gd₄(Al_1-xGa_x)₂O₉ (x = 0.0-1.0) were prepared at 1600 °C for 5 h in air. The unit cell volume of the compounds increased from 0.853 to 0.878 nm³ with x. Phase transitions having a temperature hysteresis were observed from 1100° to 1400 °C by calorimetry and dilatometry. The transition temperature increased with x. The volume of the high-temperature phase was 0.5% smaller than that of the low-temperature phase at the transition temperature. The volume changes were independent of x. The hysteresis width observed by the dilatometry was about 300 °C for the Gd₄Al₂O₉ ceramics (grain size: about 1 μm) and decreased to 50 °C for the Gd₄(Al_0.2Ga_0.8)₂O₉ ceramics (grain size: over 10 μm). Gd₄Ga₂O₉ was unstable at low temperature and decomposed to Gd₃GaO₆ and Gd₃Ga₅O₁₂ during the thermal analyses.