Selective Brookite Polymorph Formation Related to the Amorphous Precursor State in TiO₂ Thin Films

Journal Article · Thu Nov 08 00:00:00 EST 2018 · Journal of Non-Crystalline Solids

DOI:https://doi.org/10.1016/j.jnoncrysol.2018.10.049· OSTI ID:1485571

Mangum, John S. ^[1]; Agirseven, Okan ^[2]; Haggerty, James E. S. ^[2]; Perkins, John D. ^[3]; Schelhas, Laura T. ^[4]; Kitchaev, Daniil A. ^[5]; Garten, Lauren M. ^[3]; Ginley, David S. ^[3]; Toney, Michael F. ^[4]; Tate, Janet ^[2]; Gorman, Brian P. ^[1]

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1. Colorado School of Mines, Golden, CO (United States)
2. Oregon State Univ., Corvallis, OR (United States)
3. National Renewable Energy Lab. (NREL), Golden, CO (United States)
4. SLAC National Accelerator Lab., Menlo Park, CA (United States)
5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

A wide variety of brookite TiO₂ synthesis methods have been published over the past several decades, but few studies discuss the underlying mechanism that stabilizes brookite over its stable counterparts, rutile and anatase. Here in this study, we investigate of the effect of pulsed laser deposition parameters on the as-deposited amorphous precursor titania thin films, which subsequently crystallize into stable and metastable TiO₂ polymorphs upon annealing. We find that oxygen pressure in the deposition chamber strongly influences the non-equilibrium state of the amorphous precursor, which ultimately allows for selective polymorph formation. Rutile forms as the dominant phase at low pO₂ < 0.1 mTorr, while anatase is favored at high pO₂ > 5 mTorr. Brookite forms primarily at intermediate pO₂ (0.5-1.0 mTorr). Controlling the amorphous structure (i.e. Ti - O bonding and polyhedral arrangement) of the precursors via oxygen deficiency is therefore likely for the selective formation of crystalline TiO₂ polymorphs from sub-stoichiometric amorphous precursors. Lastly, directing phase selectivity by manipulating the structure and internal energy of the precursor amorphous state may have tremendous potential for synthesis of metastable crystalline phases that exhibit more desirable properties in comparison to their stable counterparts.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Next Generation of Materials by Design: Incorporating Metastability (CNGMD); National Renewable Energy Lab. (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC36-08GO28308; AC3608GO28308
• OSTI ID: 1485571
• Alternate ID(s): OSTI ID: 1635947
• Report Number(s): NREL/JA-5K00-72918
• Journal Information: Journal of Non-Crystalline Solids, Vol. 505, Issue C; ISSN 0022-3093
• Publisher: Elsevier
• Country of Publication: United States
• Language: English