Composite ceramics of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 (BSTN) with coexistence of barium strontium titanate, Ba1-xSrxTiO3 (BST), and strontium barium niobate, SrxBa1-xNb2O6(SBN) phases were successfully prepared in situ by controlling excess components according to a specially designed formula of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 and by using a traditional ceramic process. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersion spectrometer (EDS) were used to characterize the phase composition, morphology and the micro-area chemical composition of the composite ceramics. The results showed that the SBN tungsten bronze phase appeared and coexisted stably with the BST perovskite phase when the excess content of Nb2O5 was>6mol%, whereas the BST perovskite phase formed and coexisted stably with the SBN tungsten bronze phase when the excess content of TiO2 was >5.3mo1%. In the case of the two phases being equivalent to each other in BSTN composite ceramics, Nb2O5 was hard to be resolved into the perovskite phase, however, a few of TiO2 was easy to be resolved in the tungsten bronze phase. The microstructure of the composite ceramics were consisted of two kinds of grains. The smaller polygonal grains were belonged to the BST phase, and the larger ones to the SBN phase. The coexistence of the two phases inhibited the growth of the BST crystal. The density of microstructure of the composite ceramic was higher than that of both the pure BST and SBN calcined at the same temperature for the same time.
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