Combinatorial Discovery of Lanthanum-Tantalum Oxynitride Solar Light Absorbers with Dilute Nitrogen for Solar Fuels Applications
Abstract
Oxynitrides with the photoelectrochemical stability of oxides and desirable band energetics of nitrides comprise a promising class of materials for solar photochemistry. Challenges in synthesizing a wide variety of oxynitride materials has limited exploration of this class of functional materials, which we address using a reactive cosputtering combined with rapid thermal processing method to synthesize multi-cation–multi-anion libraries. We demonstrate the synthesis of a La_xTa_(1–x)O_yN_z thin film composition spread library and its characterization by both traditional thin film materials characterization and custom combinatorial optical spectroscopy and X-ray absorption near edge spectroscopy (XANES) techniques, ultimately establishing structure-chemistry-property relationships. We observe that over a substantial La–Ta composition range the thin films crystallize in the same perovskite LaTaON2 structure with significant variation of anion chemistry. The relative invariance in optical band gap demonstrates a remarkable decoupling of composition and band energetics so that the composition can be optimized while retaining the desirable 2 eV band gap energy. We also demonstrate the intercalation of diatomic nitrogen into the La_3TaO_7 structure, which gives rise to a direct-allowed optical transition at 2.2 eV, less than half the value of the oxide's band gap. These findings motivate further exploration of the visible light response of this material that is predicted to be stable over a wide range of electrochemical potential.
Additional Information
© 2017 American Chemical Society. Received: September 29, 2017; Revised: November 20, 2017; Published: November 27, 2017. This study is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy (Award No. DE-SC0004993). The authors thank Dr. Chi Ma and Prof. George R. Rossman for assistance with WDS measurements. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. The authors also thank Yi-Sheng Liu, Li Cheng Kao, and Yifan Ye for assistance with XANES measurements at ALS beamline 6.3.1.2. The authors declare no competing financial interest.Attached Files
Supplemental Material - co7b00143_si_001.pdf
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Additional details
- Eprint ID
- 83651
- DOI
- 10.1021/acscombsci.7b00143
- Resolver ID
- CaltechAUTHORS:20171204-074721984
- Department of Energy (DOE)
- DE-SC0004993
- Department of Energy (DOE)
- DE-AC02-05CH11231
- Created
-
2017-12-13Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field
- Caltech groups
- JCAP