A combinatorial guide to phase formation and surface passivation of tungsten titanium oxide prepared by thermal oxidation

Sebastian Siol; Noémie Ott; Michael Stiefel; Max Döbeli; Patrik Schmutz; Lars P. H. Jeurgens; Claudia Cancellieri

doi:10.1016/j.actamat.2019.12.026

paper

A combinatorial guide to phase formation and surface passivation of tungsten titanium oxide prepared by thermal oxidation

arXiv:1908.10067 · doi:10.1016/j.actamat.2019.12.026

Abstract

TiO $_{2}$ and WO $_{3}$ are two of the most important earth-abundant electronic materials with applications in countless industries. Recently alloys of WO $_{3}$ and TiO $_{2}$ have been investigated leading to improvements of key performance indicators for a variety of applications ranging from photo-electrochemical water splitting to electrochromic smart windows. These positive reports and the complexity of the ternary W-Ti-O phase diagram motivate a comprehensive experimental screening of this phase space. Using combinatorial thermal oxidation of solid solution W $_{1 - x}$ Ti $_{x}$ precursors combined with bulk and surface analysis mapping we investigate the oxide phase formation and surface passivation of tungsten titanium oxide in the entire compositional range from pure WO $_{3}$ to TiO $_{2}$ . The system shows a remarkable structural transition from monoclinic over cubic to tetragonal symmetry with increasing Ti concentration. In addition, a strong Ti surface enrichment is observed for precursor Ti-concentrations in excess of 55 at.%, resulting in the formation of a protective rutile-structured TiO $_{2}$ surface layer. Despite the structural transitions, the optical properties of the oxide alloys remain largely unaltered demonstrating an independent control of multiple functional properties in W $_{1 - x}$ Ti $_{x}$ O $_{n}$ . The results from this study provide valuable guidelines for future development of W $_{1 - x}$ Ti $_{x}$ O $_{n}$ for electronic and energy applications, but also novel engineering approaches for surface functionalization and additive manufacturing of Ti-based alloys.

A combinatorial guide to phase formation and surface passivation of tungsten titanium oxide prepared by thermal oxidation

Abstract

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