Selective Brookite Polymorph Formation Related to the Amorphous Precursor State in TiO2 Thin Films
- Colorado School of Mines, Golden, CO (United States)
- Oregon State Univ., Corvallis, OR (United States)
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- 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:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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