Investigation on the valence state of Te ions in the Bi6Ti5TeO22 thin film using X-ray photoelectron spectroscopy

Bi6Ti5TeO22 (BTT) thin films were grown on a Pt/Ti/SiO2/Si(1 0 0) substrate under various conditions and the valence state of the Te ion was investigated. For the BTT films grown at 300 °C, most of the Te ions existed as Te4+ ions. However, for the 10 mol% Mn-added BTT films grown at 300 °C, Te6+ ions were found even in the film grown under low oxygen partial pressure (OPP) and their number increased with increasing OPP. This increase was attributed to the presence of Mn2+ ions, which assisted the transition of Te4+ ions to Te6+ ions in order to maintain the charge balance of the Ti4+ sites. Furthermore, in the films grown at 300 °C under a high OPP of 80.0 Pa and subsequently annealed at 600 °C under a high oxygen pressure of 101 kPa, most of the Te ions existed as Te6+ ions. However, for the film grown at 300 °C under low OPP, even though the film was annealed under a high oxygen pressure of 101 kPa, only a few of Te6+ ions were formed, whereas most of Te ions remained as the Te4+ ions.