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

Authors

• E. M. Levin, Ames Laboratory DOEFollow
• B. A. Cook, Ames Laboratory DOE
• K. Ahn, Northwestern University
• M. G. Kanatzidis, Northwestern University
• Ames Laboratory DOE, Ames Laboratory DOE

Date of this Version

2009

Citation

Physical Review B 80, 115211 2009; DOI: 10.1103/PhysRevB.80.115211

Abstract

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 Ag_1−yPb₁₈Sb_1+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-n 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.