Thermoelectric properties of polycrystalline Ba2-xLaxCaMoO6-δ: Ultralow thermal conductivity and high seebeck coefficient

The high-temperature thermoelectric properties of Ba 2-x La x CaMoO 6-δ (x = 0, 0.05, 0.1, 0.15, 0.2) double perovskites were systematically investigated and reported for the first time. Through solid-state synthesis, phase-pure cubic double-perovskite oxides with the general formula Ba 2-x La x CaMoO 6-δ (0 ≤ x ≤ 0.2) were successfully synthesized. Comprehensive characterization techniques including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses demonstrated the effective incorporation of La 3+ ions into the crystal lattice, forming a homogeneous substitutional solid solution within the molybdate-based matrix. Notably, the structural integrity of the double-perovskite framework was maintained throughout the doping series, as evidenced by Rietveld refinement of the XRD patterns. The temperature-dependent charge transport properties were analyzed to correlate La 3+ substitution levels with thermoelectric performance. In the 323–1073 K range, La doping significantly reduces total thermal conductivity, which remains very low due to high atomic density and strong structural disorder. At 1073 K, Ba 1.9 La 0.1 CaMoO 6-δ achieves a thermal conductivity of 1.32 W m −1  K −1 and a Seebeck coefficient of 282.7 μV/K. These findings suggest that if effective optimization strategies are implemented to reduce resistivity, this molybdate-based materials could become promising candidates for efficient thermoelectric generators in industrial waste heat recovery systems or for stable energy conversion in next-generation aerospace power devices, where high temperature stability and low thermal conductivity are essential.