The concept of grain-boundary complexions has been extended to specialty alumina powders with the goal of deconvoluting the effects of second phase and complexion transitions on microstructure evolution. Two powder compositions with significantly different impurity levels were examined to study the effect of second phase content. The changes in grain size distribution after postsintering annealing for the two compositions were analyzed in order to identify complexion transitions. An analysis technique was developed using probability plots to separate distinct populations of grains of different size regimes. There was evidence of multiple transitions in each material as evidenced by multiple grain size populations. A higher amount of second phase in one powder suppressed the effects of the transitions making the microstructural inhomogeneities less pronounced.