Effect of the annealing temperature on the structural and multiferroic properties of mullite Bi₂Fe₄O₉ thin films

Mullite Bi₂Fe₄O₉ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. The deposited Bi₂Fe₄O₉ thin films were annealed at a series of temperatures in the range 700–850 °C in an oxygen atmosphere using a rapid thermal annealing process. The effect of the annealing temperature on the structural, electrical and multiferroic properties of the Bi₂Fe₄O₉ thin films was investigated. The results showed that the Bi₂Fe₄O₉ thin film that was annealed at 800 °C exhibits a well-crystallized orthorhombic phase with the complete absence of secondary phases, in marked contrast to the thin films that were annealed at 700, 750, and 850 °C for which the formation of secondary phases was observed. Moreover, the Bi₂Fe₄O₉ thin film that was annealed at 800 °C was found to exhibit a low leakage current density and enhanced multiferroic properties, both of which are indicative of the formation of a pure mullite phase with a stable structure.