Laser processing of calcium manganite-based materials for thermoelectric generators

Thermoelectric oxides are emerging as a promising alternative to traditional thermoelectric materials due to their high-temperature stability, low cost, and abundance. In this work, we investigate the Laser Floating Zone (LFZ) technique for processing Ca1-xNdxMnO3 with different Nd concentrations (x = 0, 0.05, 0.1, 0.2), grown at various pulling rates (25 and 100 mm h−1). The impact of the sample's composition and processing conditions on the microstructure and thermoelectric performance was analysed. X-ray diffraction results confirmed the formation of the major perovskite-type structure, favoured by the slower pulling rate. Scanning electron microscopy/energy dispersive spectroscopy showed high-density, non-porous structure of the samples, with uniform Nd distribution. Electrical conductivity and Seebeck coefficient measurements, conducted in air from 500 K to 1200 K, demonstrated an expected correlated trend between these properties, with electrical conductivity increasing and the Seebeck coefficient decreasing upon doping. Similar measurements were made for the thermal conductivity, from 500 to 1100 K, which showed a decrease with increasing Nd content, an expected behaviour. The highest power factor (168.6 μW m−1K−2) and the highest figure of merit (0.14) were achieved for Ca0.95Nd0.05MnO3 grown at a 100 mm h−1 at 1173 K. These values are within those reported for conventional solid-state reaction samples. A prototype unileg thermoelectric module based on Ca0.95Nd0.05MnO3 was fabricated and tested, yielding a maximum power output of 298 μW under a thermal gradient of 483 K. These findings demonstrate that LFZ growth is a viable method for producing efficient oxide thermoelectrics for intermediate-to high-temperature energy harvesting applications.