A wet-chemical synthesis and microwave calcination approach was found to be efficient for synthesizing alpha-alumina powders and polycrystals with high levels of lattice defects. The defects of the as-produced powders were determined from the optical transmittance of spark-plasma-sintered compacts with an identical microstructure using a conventional calcination method. The existence of a high lattice defect concentration was verified by positron annihilation lifetime analysis and X-ray diffraction. The microwave-activated lattice defect phenomenon has potential applications in the production of semiconductor materials or films with high chemical activity or crystal doping. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.