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Towards sustainable energy: photocatalysis of Cr-doped TiO2. 5. Effect of segregation on surface versus bulk composition

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Abstract

The present chain of five papers considers the concept of solar-to-chemical energy conversion using TiO2-based semiconductors. The series reports the effect of chromium on the key performance-related properties of polycrystalline TiO2 (rutile), including electronic structure, photocatalytic activity, intrinsic defect disorder, electrochemical coupling and surface versus bulk properties. This work considers the effect of oxygen activity on segregation-induced surface versus bulk composition for both polycrystalline and single-crystal specimens of Cr-doped TiO2. It has been documented that annealing of Cr-doped TiO2 at 1273 K in oxidising conditions results in an enrichment and depletion of the surface layer with chromium. It is shown that the segregation-induced enrichment factor for single crystal is substantially larger than that for polycrystalline specimen. The effect is considered in terms of a theoretical model showing that surface segregation of solute in polycrystalline specimen is encumbered by its segregation to grain boundaries. It is also shown that the segregation-induced enrichment is profoundly influenced by oxygen activity. The new insight of this work involves (i) the determination of well-defined chromium segregation in Cr-doped TiO2, including single-crystal and polycrystalline specimens, after annealing in the gas phase of controlled oxygen activity, and (ii) identification of the predominant driving force of segregation of chromium in Cr-doped TiO2 that is based on electrostatic interactions between the low-dimensional surface structure (LDSS) and electrically charge segregating species.

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Authors and Affiliations

  1. Solar Energy Technologies, School of Computing, Engineering and Mathematics, Western Sydney University, Penrith, NSW, 2751, Australia

    Kazi Akikur Rahman, Tadeusz Bak & Janusz Nowotny

  2. Australian Nuclear Science and Technology Organisation, Institute of Environmental Research, Locked Bag 2001, Kirrawee DC, NSW, 2232, Australia

    Armand Atanacio & Mihail Ionescu

  3. Secondary Ion Mass Spectrometry Facility, Office of the Deputy Vice Chancellor (Research and Development), Western Sydney University, Building M8, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW, 2751, Australia

    Rong Liu

Authors
  1. Kazi Akikur Rahman
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  2. Tadeusz Bak
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  3. Armand Atanacio
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  4. Mihail Ionescu
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  5. Rong Liu
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  6. Janusz Nowotny
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Corresponding author

Correspondence to Janusz Nowotny.

Additional information

New insight

1. The determination of well-defined chromium segregation in Cr-doped TiO2, including single-crystal and polycrystalline specimens, after annealing in the gas phase of controlled oxygen activity.

2. The results of surface and bulk analysis are reflective of the effect of oxygen activity on bulk versus surface defect disorder of TiO2-based solid solutions for both single-crystal and polycrystalline specimens.

3. The predominant driving force of segregation of chromium in Cr-doped TiO2 is based on electrostatic interactions between the low-dimensional surface structure (LDSS) and electrically charged lattice elements.

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Rahman, K.A., Bak, T., Atanacio, A. et al. Towards sustainable energy: photocatalysis of Cr-doped TiO2. 5. Effect of segregation on surface versus bulk composition. Ionics 24, 1211–1219 (2018). https://doi.org/10.1007/s11581-017-2326-0

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  • DOI: https://doi.org/10.1007/s11581-017-2326-0

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