Ecobenign and high-temperature-stable oxides are considered a promising alternative to traditional Bi2Te3-, Bi2Se3-, and PbTe-based thermoelectric materials. The quest for high-performing thermoelectric oxides is still open and, among other challenges, includes the screening of various materials systems for potentially promising electrical and thermal transport properties. In this work, a new family of acceptor-substituted Haldane gap 1D BaGd2CoO5 dense ceramic materials was characterized in this respect. The substitution of this material with calcium results in a general improvement of the electrical performance, contributed by an interplay between the charge carrier concentration and their mobility. Nevertheless, a relatively low electrical conductivity was measured, reaching ∼5 S/cm at 1175 K, resulting in a maximum power factor of ∼25 μW/(K × m2) at 1173 K for BaGd1.80Ca0.20CoO5. On the other hand, the unique anisotropic 1D structure of the prepared materials promotes efficient phonon scattering, leading to low thermal conductivities, rarely observed in oxide electroceramics. While the BaGd2–xCaxCoO5 materials show attractive Seebeck coefficient values in the range 210–440 μV/K, the resulting dimensionless figure of merit is still relatively low, reaching ∼0.02 at 1173 K. The substituted BaGd2–xCaxCoO5 ceramics show comparable thermoelectric performance in both inert and air atmospheres. These features highlight the potential relevance of this structure type for thermoelectric applications, with future emphasis placed on methods to improve conductivity.

N.N. acknowledges funding from DST under the Inspire faculty program (DST/INSPIRE/04/2017/003334) and C-MET, MeitY, Govt. of India. D.P.F. acknowledges the FCT Investigator Programme IF/01344/2014/CP1222/CT0001 and Projects PTDC/CTM-ENE/6319/2014, POCI-01-0145-FEDER-032241, UID/EMS/00481/2019-FCT, CENTRO-01-0145-FEDER-022083-QREN, FEDER, COMPETE Portugal and EU for financial support. A.V.K., S.R., and G.C. acknowledge the support of the project POCI-01-0145-FEDER-031875, financed by the COMPETE 2020 Program and National Funds through the FCT/MEC and, when applicable, cofinanced by FEDER under the PT2020 Partnership Agreement, and the support of the FCT-CEECIND/02608/2017 grant. This work was partially developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020, financed by national funds through the FCT/MCTES. W.X. and A.W. acknowledge the financial support from Deutsche Forschungsgemeinschaft (Project No. BA 4171/4-1).