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Issue 36, 2017
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Multicomponent equiatomic rare earth oxides with a narrow band gap and associated praseodymium multivalency

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Abstract

New multicomponent equiatomic rare earth oxides (ME-REOs) containing 3–7 rare earth elements (Ce, Gd, La, Nd, Pr, Sm and Y) in equiatomic proportions are synthesized using nebulized spray pyrolysis. All the systems crystallized as a phase pure fluorite type (Fm[3 with combining macron]m) structure in spite of the high chemical complexity. A nominal increase in the lattice parameter compared to CeO2 is observed in all ME-REOs. X-ray photoelectron spectroscopy performed on the ME-REOs confirmed that all the constituent rare earth elements are present in the 3+ oxidation state, except for Ce and Pr which are present in 4+ and in a mixed (3+/4+) oxidation state, respectively. The presence of Ce4+ contributes substantially to the observed stability of the single phase structure. These new oxide systems have narrow direct band gaps in the range of 1.95–2.14 eV and indirect band gaps in the range of 1.40–1.64 eV, enabling light absorption over the entire visible spectral range. Furthermore, the oxygen vacancy concentration rapidly increases and then saturates with the number of rare earth elements that are incorporated into the ME-REOs. The lowering of the band gap is found to be closely related to the presence of multivalent Pr. Interestingly, the band gap values are relatively invariant with respect to the composition or thermal treatments. Considering the high level of oxygen vacancies present and the observed low band gap values, these new material systems can be of importance where the presence of oxygen vacancies is essential or in applications where a narrow band gap is desirable.

Graphical abstract: Multicomponent equiatomic rare earth oxides with a narrow band gap and associated praseodymium multivalency

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Publication details

The article was received on 07 Jun 2017, accepted on 18 Aug 2017 and first published on 21 Aug 2017


Article type: Paper
DOI: 10.1039/C7DT02077E
Citation: Dalton Trans., 2017,46, 12167-12176
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    Multicomponent equiatomic rare earth oxides with a narrow band gap and associated praseodymium multivalency

    A. Sarkar, C. Loho, L. Velasco, T. Thomas, S. S. Bhattacharya, H. Hahn and R. Djenadic, Dalton Trans., 2017, 46, 12167
    DOI: 10.1039/C7DT02077E

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