In the present study, we synthesized Nb- or Ta-doped BaSnO₃ ceramics and characterized the thermal conductivities. The doped samples BaSn_1-xM_xO_3-δ (M = Nb or Ta, x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized by solid state reactions followed by spark plasma sintering (SPS). The lattice parameters of BaSn_1-xNb_xO_3-δ and BaSn_1-xTa_xO_3-δ increased almost linearly with increasing the doping level, then remained constant at x = 0.10 and x = 0.15, respectively. After the solubility limit, peaks for Ba₂SnO₄ were observed in the powder XRD patterns of both the Nb- and Ta-doped samples. The thermal conductivity of BaSn_0.95Nb_0.05O_3-δ was clearly lower than that of BaSn_0.95Ta_0.05O_3-δ , mainly caused by its small speed of sounds and a short mean free pass of phonons compared with those of BaSn_0.95Ta_0.05O_3-δ.

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