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.

To achieve a better material for thermoelectric power generation device, filled skutterudite Yb_0.3Co₄Sb₁₂ samples were fabricated by melting-quenching-annealing-spark plasma sintering (SPS) method. Two sets of samples, before and after SPS, were investigated. In both the two sets of samples, the average grain size of the samples increases monotonously with the increase of annealing time, while Yb filling fraction firstly increases and then decreases. Yb not filling into the skutterudite remains at the grain boundaries in the form of Yb₂O₃ after SPS, which could be quantified by the spatially difference method of energy dispersive spectra. Step distribution of Yb filling fraction was observed in the samples annealed for 1 h, which was caused by the microstructural evolution from the peritectic phases to the skutterudite phase. The sample annealed for 3 days and SPS sintered possesses the maximum value of Yb filling fraction 0.249 and the maximum ZT value of 1.24 at 850 K. These results are helpful to better understand the microstructural evolution and Yb filling behavior in skutterudite materials.