Abstract: The 0～20mol%Er³⁺-doped γ-AlOOH gels were prepared by using sol-gel methods from the aluminium
isopropoxide [Al(OC₃H₇)₃]-derived Al₂O₃ sols. The phase structures and these transformation processes of Er³⁺-doped γ-AlOOH gels
sintered at 950～1400℃ were investigated by using X-ray diffraction (XRD) and differential thermal analysis (DTA). The experimental
results show that Er³⁺ doping lead to restraining the phase transformation of θ→α for alumina, and decreasing the growth rate of α phase
with an increase of 50～70℃ for the completed transformation temperature. The precipitation of the two Er-Al-O compounds, i.e.
Al₁₀Er₆O₂₄ and ErAlO₃ phases, is dependent on the Er³⁺ doping concentration and the sintering temperature. The ErAlO₃
phase precipitates in the 1～5mol%Er³⁺-doped Al₂O₃ sintered at 1100～1200℃. The Al_{10Er_6O_{24 phase precipitates in the 5～20mol%Er³⁺-doped Al₂O₃ sintered at
1000～1100℃, and is in all Er³⁺-doped Al₂O₃ with further increasing the sintering temperature. The nucleation of phase
transformation for θ→α is accelerated due to the presence of ErAlO₃ phase, resulting in a decrease of 30～50℃ for the beginning temperature of phase transformation correspondingly.
It has no greatly influence on the growth rate of α phase. The Al₁₀Er₆O₂₄ phase does not affect the phase transformation for
θ→α

Key words: boehmite gel, Er³⁺ doping, phase transformation, sol-gel