(High Temperature Materials Division Outstanding Achievement Award) Semiconducting Properties and Defect Disorder of Indium-Doped Titanium Dioxide

Rutile is the promising inexpensive raw material for processing photocatalysts for solar water disinfection and photoelectrodes for solar hydrogen fuel (1). This work studied the effect of indium on surface vs. bulk electrical properties and the related defect disorder of TiO₂ (rutile). It is shown that the effect of oxygen activity on both thermoelectric power and electrical conductivity of In-doped TiO₂, determined at 1023 K – 1273 K in the gas phase of controlled oxygen activity [10^-16 Pa<p(O₂)<10⁵ Pa], is consistent with a dual mechanism of indium incorporation, involving acceptor energy levels in the bulk and donor levels at the interface. The latter process leads to the formation of a quasi-isolated thin interface layer that differs from the bulk phase in the semiconducting properties and the related defect disorder as a result of segregation. This conclusion is supported by surface analysis of secondary ion mass spectrometry (SIMS) showing strong indium segregation towards negatively charged surface layer enriched by titanium vacancies (2). It is shown that the semiconducting properties may be modified in a controlled manner by defect engineering. It is also shown that segregation may be used as the technology in processing TiO₂ with desired surface vs. bulk semiconducting properties that are required to form high-performance photoelectrodes for production of solar hydrogen fuel using photoelectrochemical cells and photocatalysts for water purification from toxic contaminants, such as bacteria, using solar energy as the only driving force of the process.  The related studies are being conducted by parallel projects within the UWS R&D program on solar water decontamination and the generation of solar fuel.

 

Acknowledgements

The support was provided by the University of Western Sydney through the FIR program.

References

1. A Fujishima, K Honda, Nature 238 (1972) 37

A. Atanacio, T. Bak, J. Nowotny, ACS Appl Mater. & Interf., 4 (2012) 6626