Electronic inhomogeneity and Ag:Sb imbalance of Ag1-yPb18Sb1+zTe20 high-performance thermoelectrics elucidated by 125Te and 207Pb NMR

E.M. Levin, B.A. Cook, K. Ahn, M.G. Kanatzidis, K. Schmidt-Rohr



 Using magic-angle spinning 125Te and 207Pb NMR, we have discovered the presence of two phases of approximately tenfold different free-electron concentration, n, in high-performance thermoelectrics Ag1−yPb18Sb1+zTe20 (“LAST-18”), proven by pairs of Knight-shifted NMR peaks and biexponential spin-lattice relaxation. The ratio of the phases is typically 2:1 with n≈2×1019 cm−3 and 0.2×1019 cm−3, respectively, determined from the spin-lattice relaxation times. 125Te NMR spectra show that both phases contain similar concentrations of Sb. The low-n component is assigned to Ag-rich regions with Ag-Sb pairing (but not AgSbTe2), the dominant high-ncomponent to PbTe:Sb resulting from the excess of Sb relative to Ag. The electronic inhomogeneity observed here must be considered in the search for a better understanding of high-performance thermoelectric materials.

Link to article - American Institute of Physics

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