Ceramics of Ba(Mg 1 / 3 Ta 2 / 3 )O 3 -BaSnO 3 (BSMT) are synthesized by a two-stage calcination method. Microstructures are analyzed, using X-ray diffractometry, transmission electron microscopy, Raman spectroscopy, and scanning electron microscopy. The addition of BaSnO 3 reduces the cation ordering of Ba(Mg 1 / 3 Ta 2 / 3 )O 3 and its sinterability. Variations in ordered structure with BaSnO 3 content are revealed by the reduction in intensity of the superlattice reflections, the domain size, the c/a ratio, and the shifting and broadening in Raman lines. The relations between microstructure and quality factors of BSMT are discussed. (C)