title: Sub-millisecond (125)Te NMR spin-lattice relaxation times and large Knight shifts in complex tellurides: Validation of a quadratic relation across the spectrum.
abstract: (125)Te NMR spectra and spin-lattice relaxation times, T1, have been measured for several GeTe-based materials with Te excess. The spectra show inhomogeneous broadening by several thousand ppm and a systematic variation in T1 relaxation time with resonance frequency. The quadratic dependence of the spin-lattice relaxation rate, 1/T1, on the Knight shift in the Korringa relation is found to be valid over a wide range of Knight shifts. This result confirms that T1 relaxation in GeTe-based materials is mostly dominated by hyperfine interaction between nuclei and free charge carriers. In GeTe with 2.5% excess of Te, about 15% of the material exhibits a Knight shift of ≥4500ppm and a T1 of only 0.3ms, indicating a high hole concentration that could correspond to close to 50% vacancies on the Ge sublattice in this component. Our findings provide a basis for determining the charge carrier concentration and its distribution in complex thermoelectric and phase-change tellurides, which should lead to a better understanding of electronic and thermal transport properties as well as chemical bonding in these materials.
authors.affiliation: Division of Materials Sciences and Engineering, Ames Laboratory U.S. Department of Energy (DOE), Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA. Electronic address: levin@iastate.edu.
authors.forename: E M
authors.initials: EM
authors.lastname: Levin
authors.affiliation: Department of Chemistry, Iowa State University, Ames, IA 50011, USA.
authors.forename: J-F
authors.initials: JF
authors.lastname: Cui
authors.affiliation: Division of Materials Sciences and Engineering, Ames Laboratory U.S. Department of Energy (DOE), Ames, IA 50011, USA; Department of Chemistry, Iowa State University, Ames, IA 50011, USA. Electronic address: srohr@brandeis.edu.
authors.forename: K
authors.initials: K
authors.lastname: Schmidt-Rohr
keywords: (125)Te NMR; Complex tellurides; Knight shift; Korringa relation; Spin-lattice relaxation