Synthesis of thermodynamically stable corundum structure alumina under lower temperature is of great significance in practical applications, exploration on new technique and the involved mechanism therefore becomes increasingly essential. In this work, the coupling effect and mechanism of chromia doping and vacuum condition on the phase transition of Al2O3 prepared via co-precipitation process were investigated and explored. It was found that chromia doping by itself did not promote the nucleation of alpha-Al2O3, or in some sense inhibited the transformation process. Cr doped gamma-Al2O3 powders treated in a vacuum condition (10(-5) Pa) however showed a gradual transition to alpha-Al2O3 even at low temperature of 600 degrees C, demonstrating that surface nucleation sites introduced by a coupled effect of vacuum and Cr2O3 doping contributed to the dramatic reduction (200-400 degrees C) of the phase transformation temperature. Based on the comprehensive characterizations and conventional diffusional nucleation mechanism, it is concluded that the surface nucleation sites for phase change to alpha-Al2O3 increased significantly during vacuum calcination with the combination of template effects of Cr2O3. This finding may provide a new way in fabrication and understanding of stable alumina formation under relatively moderate temperature condition. (C) 2016 Elsevier B.V. All rights reserved.