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Redox-mediated transformation of a Tb2O3(111) thin film from the cubic fluorite to bixbyite structure

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Abstract

We used temperature programmed desorption (TPD) and low energy electron diffraction (LEED) to investigate the isomeric structural transformation of a Tb2O3 thin film grown on Pt(111). We find that repeated oxidation and thermal reduction to 1000 K transforms an oxygen-deficient, cubic fluorite (CF) Tb2O3(111) thin film to the well-defined bixbyite, or c-Tb2O3(111) structure, whereas annealing the CF-Tb2O3(111) film in UHV is ineffective in causing this structural transformation. We estimate that the final stabilized film consists of about ten layers of c-Tb2O3(111) in the surface region plus about eight layers of CF-Tb2O3(111) located between the c-Tb2O3(111) and the Pt(111) substrate. Our measurements reveal the development of two distinct O2 TPD peaks during the CF to bixbyite transformation that arise from oxidation of c-Tb2O3 domains to the stoichiometrically-invariant ι-Tb7O12 and δ-Tb11O20 phases and demonstrate that the c-Tb2O3 phase oxidizes more facilely than CF-Tb2O3. We present evidence that nucleation and growth of c-Tb2O3 domains occurs at the buried TbOx/CF-Tb2O3 interface, and that conversion of the interfacial CF-Tb2O3 to bixbyite takes place mainly during thermal reduction of TbOx above ∼900 K and causes newly-formed c-Tb2O3 to advance deeper into the film. The avoidance of low Tb oxidation states may facilitate the CF to bixbyite transformation via this redox mechanism.

Graphical abstract: Redox-mediated transformation of a Tb2O3(111) thin film from the cubic fluorite to bixbyite structure

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Publication details

The article was received on 15 Sep 2019, accepted on 01 Dec 2019 and first published on 02 Dec 2019


Article type: Paper
DOI: 10.1039/C9CP05083C
Phys. Chem. Chem. Phys., 2020, Advance Article

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    Redox-mediated transformation of a Tb2O3(111) thin film from the cubic fluorite to bixbyite structure

    C. J. Lee, A. Sayal, S. Vashishtha and J. F. Weaver, Phys. Chem. Chem. Phys., 2020, Advance Article , DOI: 10.1039/C9CP05083C

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