EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Waste heat originated by industrial and combustive processes or harvested directly from natural heat sources (i.e. sun, geothermal processes, ambient heat etc.) can be converted into electricity by means of thermoelectric modules. These devices use the ability of particular materials to convert heat gradients into voltage by means of the so called Seebeck effect. Thermoelectric generators have found applications in aerospace, automotive, sensors, medical, and domestic applications; therefore, the study and the optimization of such materials is crucial for achieving higher conversion efficiencies and reducing manufacturing costs.
The thermoelectric Co2(Zr,Hf)Sn alloys were synthesized and characterized for the first time. Bulk samples were prepared by arc-melting the metallic elements and subsequent annealing. Structural and microstructural characterizations were performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). Thermoelectric characterization was performed by measuring the electronic transport properties. Seebeck coefficient measurements show a n-type behaviour for both alloys, with a monotonous increasing trend from room temperature to about 450 K. Between 450 K and 773 K, the Seebeck coefficient remains rather constant around -33 µV/K and -37 µV/K for Co2ZrSn and Co2HfSn, respectively. The electrical conductivity of both Co2ZrSn and Co2HfSn show a decreasing trend (i.e., metallic behaviour) from room temperature to about 450 K, followed by an increasing trend (i.e., semiconducting behaviour). The sharp transition from the metallic to the semiconducting behaviour observed around 450 K occurs in correspondence of the transition from ferromagnetic to paramagnetic behaviour at the Curie temperature of these compounds and can be associated to a change in the density of states (DOS) profile.