UV-Driven Oxygen Surface Exchange and Stoichiometry Changes in a Thin-Film, Nondilute Mixed Ionic Electronic Conductor, Sr(Ti,Fe)O3-d.
J Am Chem Soc
; 146(33): 23265-23277, 2024 Aug 21.
Article
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| MEDLINE
| ID: mdl-39165247
ABSTRACT
Enabling light-controlled ionic devices requires insight into photoionic responses in technologically relevant materials. Mixed-conducting perovskites containing nondilute Feâserving as electrodes, catalysts, and sensorsâcan support large, electronically accommodated excursions in oxygen content, typically controlled by temperature, bias, and gas atmosphere. Instead, we investigated the ability of low-fluence, above-bandgap illumination to adjust oxygen stoichiometry and drive oxygen fluxes in nondilute Sr(Ti1-xFex)O3-x/2+δ (x = 0.07, 0.35) thin films with high baseline hole concentrations. Films' optical transmission at 2.8 eV was used as a probe of oxygen stoichiometry in the range â¼100-500 °C. We compared pO2-step-driven and UV (3.4 eV)-step-driven visible optical transmission relaxations in films, finding that the time constants and activation energies of the relaxations were consistent with each other and thus with oxygen-surface-exchange-limited kinetics. Blocking oxygen exchange at the solid-gas interface with a UV-transparent capping layer resulted in no UV-induced optical relaxations. These results demonstrate that above-bandgap illumination can increase oxygen content in nondilute compositions through oxygen flux into the solid from the gas. First-principles simulations of defect formation enthalpies indicate that oxygen vacancies are energetically less favorable under steady-state illumination owing to shifts in quasi-Fermi levels. A larger 2.8 eV-optical response to UV illumination in x = 0.07 vs x = 0.35 samples was further investigated through ultrafast transient spectroscopy, where it was found that the x = 0.07 sample exhibits a slower carrier recombination. Together, these results suggest potential design principles for materials supporting large stoichiometry changes under above-gap illumination (1) long excited carrier lifetimes and (2) highly charged, rather than neutral, defects/associates.
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01-internacional
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MEDLINE
Idioma:
En
Revista:
J Am Chem Soc
Año:
2024
Tipo del documento:
Article
País de afiliación:
Estados Unidos