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arXiv · 1601.07640

NMR experiments and electronic structure calculations in type-I BaAlGe clathrates

Weiping Gou·Sergio Y. Rodriguez·Yang Li·Joseph H. Ross Jr
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Abstract

We describe 27Al NMR experiments on Ba8AlxGe46-x type-I clathrates coupled with ab initio computational studies. For x=16, calculated spectra determined by the ab initio results gave good agreement with the measurements, with best-fitting configurations also corresponding to the computed lowest-energy atomic arrangements. Analysis of the NMR results showed that a distribution of Knight shifts dominates the central portion of the line. Computational results demonstrate that this stems from the large variation of carrier density on different sites. Al-deficient samples with x=12 and 13 exhibited a split central NMR peak, signaling two main local environments for Al ions, which we connected to the presence of vacancies. Modeling of the wide-line spectrum for x=12 indicates a configuration with more Al on the 24k site than for x=16. The results indicate the importance of nonbonding hybrids adjacent to the vacancies in the electronic structure near EF. We also address the static distortions from Pm-3n symmetry in these structures.

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Weiping Gou, Sergio Y. Rodriguez, Yang Li, Joseph H. Ross Jr. 2016-01-28. NMR experiments and electronic structure calculations in type-I BaAlGe clathrates. https://doi.org/10.1103/physrevb.80.144108

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