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

Abstract

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.