E.M. Levin, B.A. Cook, K. Ahn, M.G. Kanatzidis, K. Schmidt-Rohr
Using magic-angle spinningand NMR, we have discovered the presence of two phases of approximately tenfold different free-electron concentration, , in high-performance thermoelectrics (“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 and , respectively, determined from the spin-lattice relaxation times. NMR spectra show that both phases contain similar concentrations of Sb. The low- component is assigned to Ag-rich regions with Ag-Sb pairing (but not ), the dominant high- component 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.
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