Formation of metastable cubic phase and thermoelectric properties in Mg3Bi2 films deposited by magnetron sputtering

[Display omitted] •A metastable cubic phase of Mg3Bi2 that only existed under high temperatures and high pressures was observed in the sputtered Mg3Bi2 film.•A structural transition from cubic to hexagonal phase occurs as substrate temperature increases.•The n-type behavior of the cubic phase of Mg3Bi2 film was initially observed, followed by the p-type behavior of the hexagonal phase of Mg3Bi2 film. Mg3Bi2 has become a promising candidate for studying thermoelectric, Mg-ion batteries and novel topological properties. In this paper, the Mg3Bi2 thin films were deposited on glass substrates by magnetron co-sputtering under substrate temperatures ranging from 535 K to 595 K. A metastable cubic Mg3Bi2 that only existed under high temperatures and high pressures was observed in the Mg3Bi2 film deposited at Ts = 535 K. A structuralphasetransition occurs as Ts increases, and a textured hexagonal Mg3Bi2 film was obtained at Ts = 595 K. The microstructure and thermoelectric properties of cubic Mg3Bi2 and hexagonal Mg3Bi2 films were systematically investigated. The cubic Mg3Bi2 film exhibited n-type semiconductor behavior. However, the hexagonal Mg3Bi2 thin film possessed a positive Seebeck coefficient. A maximum power factor of 1.1 μWcm-1K−2 was obtained in textured hexagonal Mg3Bi2 film at 393 K. Our results could pave the way toward the engineering phase of Mg3Bi2 film, which has potential applications in micro-energy harvesting devices.