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

Article

关键词: GE;    SEMICONDUCTORS;    SR8GA16GE30;    RESONANCE;    STABILITY;    AL-27;    GA;    BA;   

DOI  :  10.1103/PhysRevB.80.144108

来源: SCIE

【 摘 要 】

We describe (27)Al NMR experiments on Ba(8)Al(x)Ge(46-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 E(F). We also address the static distortions from Pm (3) over barn symmetry in these structures.

【 授权许可】

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