Unravelling the Effects of Calcium Substitution in BaGd₂CoO₅ Haldane Gap 1D Material and Its Thermoelectric Performance

Abstract

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–x Ca x CoO5 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–x Ca x CoO5 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.

New Series of Pentanary Oxides, AM2C6Te3O18 (A = Pb, Sr; M = Mn, Cd; C = Ni, Co): Synthesis, Structure, and Magnetic and Optical Properties

“…The compounds are found to be antiferromagnetic with geometrical frustration from interchain magnetic interactions. Na 5 Co 15.5 Te 6 O 36 is yet another compound with the same structural features, where the Co 2+ chain shows 1D magnetism . The structure can also be considered to be closely related to CaZrBAl 9 O 18 and Mg 3 (BO 3 ) 3 (OH, F) 3 .…”