Epitaxial stannate pyrochlore thin films: Limitations of cation stoichiometry and electron doping

Hensling, Felix V. E.;Dahliah, Diana;Dulal, Prabin;Singleton, Patrick;Schlom, Darrell G.;et.al.
(2021) APL Materials — Vol. 9, n° 5, p. 51113 (2021)

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Authors
  • Hensling, Felix V. E.orcid-logoDepartment of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
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  • Dahliah, DianaUCLouvain
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  • Dulal, PrabinDepartment of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA
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  • Singleton, PatrickPlatform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM), Cornell University, Ithaca, New York 14853, USA
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  • Rignanese, Gian-Marcoorcid-logoUCLouvain
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  • Hautier, Geoffroyorcid-logoUCLouvain
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  • Schlom, Darrell G.orcid-logoDepartment of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
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Abstract
We have studied the growth of epitaxial films of stannate pyrochlores with a general formula A2Sn2O7 (A = La and Y) and find that it is possible to incorporate ∼ 25% excess of the A-site constituent; in contrast, any tin excess is expelled. We unravel the defect chemistry, allowing for the incorporation of excess A-site species and the mechanism behind the tin expulsion. An A-site surplus is manifested by a shift in the film diffraction peaks, and the expulsion of tin is apparent from the surface morphology of the film. In an attempt to increase La2Sn2O7 conductivity through n-type doping, substantial quantities of tin have been substituted by antimony while maintaining good film quality. The sample remained insulating as explained by first-principles computations, showing that both the oxygen vacancy and antimonyon-tin substitutional defects are deep. Similar conclusions are drawn on Y2Sn2O7. An alternative n-type dopant, fluorine on oxygen, is shallow according to computations and more likely to lead to electrical conductivity. The bandgaps of stoichiometric La2Sn2O7 and Y2Sn2O7 films were determined by spectroscopic ellipsometry to be 4.2 eV and 4.48 eV, respectively.
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Hensling, F. V. E., Dahliah, D., Dulal, P., Singleton, P., Sun, J., Schubert, J., Paik, H., Subedi, I., Subedi, B., Rignanese, G.-M., Podraza, N. J., Hautier, G., & Schlom, D. G. (2021). Epitaxial stannate pyrochlore thin films: Limitations of cation stoichiometry and electron doping. APL Materials, 9(5), 51113. https://doi.org/10.1063/5.0049334 (Original work published 2021)