Graphene controlled phase evolution in Sr-deficient Sr(Ti, Nb)O3 thermoelectric ceramics
Jia Li, Cao Wu, Jilong Huang, Juanjuan Xing, Yuchi Fan, Qingqiao Fu, Ying Jiang, Hui Gu
Abstract
Correlated phase and microstructural evolution are systematically investigated by electron microscopies in Sr-deficient Sr(Ti, Nb)O3 (STNO) thermoelectric ceramics incorporated with different fraction of reduced graphene oxide (RGO). It is found that while no impurity except for very few Ti3O5 precipitates are observed in monolithic STNO, the Nb-enriched rutile TiO2 appears in RGO/STNO composites. With increasing RGO content, the amount of precipitates increase at first and then decrease when RGO content becomes high, which can be ascribed to the formation of local Magnéli phase. In addition, the energy-dispersive X-ray spectra combined with cathodoluminescence characterization indicates that the variation of Sr deficiency experiences the opposite trend with respect to the precipitates content. These findings clearly reveal the unique reducing effect of RGO on the microstructure of doped SrTiO3 with Sr deficiency, which can greatly facilitate the design of perovskite based thermoelectric materials of hierarchical structure.