WO3 ceramics were sintered at various temperatures with a B2O3 additive, and WO3 sintering was observed at temperatures above the heat-treatment temperature of 900 degrees C. For the WO3 ceramic with B2O3 (heat-treated for 20 h), a dense microstructure with crystal facets was formed, while the numbers of pores decreased. The dielectric constant of the sintered WO3 ceramic with B2O3 additive was twice as large as that without B2O3. (C) 2015 Elsevier Ltd. All rights reserved.