Vacancy ordering and electronic structure of gamma-Fe2O3 maghemite: a theoretical investigation - Condensed Matter > Materials ScienceReportar como inadecuado




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Abstract: The crystal structure of the iron oxide gamma-Fe2O3 is usually reported ineither the cubic system space group P4332 with partial Fe vacancy disorder orin the tetragonal system space group P41212 with full site ordering andc-a\approx 3. Using a supercell of the cubic structure, we obtain the spectrumof energies of all the ordered configurations which contribute to the partiallydisordered P4332 cubic structure. Our results show that the configuration withspace group P41212 is indeed much more stable than the others, and that thisstability arises from a favourable electrostatic contribution, as thisconfiguration exhibits the maximum possible homogeneity in the distribution ofiron cations and vacancies. Maghemite is therefore expected to be fully orderedin equilibrium, and deviations from this behaviour should be associated withmetastable growth, extended anti-site defects and surface effects in the caseof small nanoparticles. The confirmation of the ordered tetragonal structureallows us to investigate the electronic structure of the material using densityfunctional theory DFT calculations. The inclusion of a Hubbard DFT+Ucorrection allows the calculation of a band gap in good agreement withexperiment. The value of the gap is dependent on the electron spin, which isthe basis for the spin-filtering properties of maghemite.



Autor: Ricardo Grau-Crespo, Asmaa Y. Al-Baitai, Iman Saadoune, Nora H. De Leeuw

Fuente: https://arxiv.org/







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