${}^{125}$Te nuclear magnetic resonance spectra and spin-lattice relaxation of $n$- and $p$-type PbTe, self-doping narrow band-gap semiconductors, have been studied and compared to those of $p$-type GeTe. Spin-lattice relaxation in GeTe can be fit by one component, while that in both PbTe samples must be fit by at least two components, showing electronically homogeneous and inhomogeneous materials, respectively. For PbTe-based materials, the spin-lattice relaxation rate 1/$T_1$ increases linearly with carrier concentration. The data for GeTe fall on the same line and allow us to extend this plot to higher concentrations. Long and short $T_1$ components in both PbTe samples reflect “low,” ∼10${}^{17}$ cm${}^{-3}$, and “high,” ∼10${}^{18}$ cm${}^{-3}$, carrier concentration components. Carrier concentrations in both $n$- and $p$-type PbTe samples obtained from the Hall and Seebeck effects generally match the “high” carrier concentration component, and to some extent, ignore the “low” one. This demonstrates that the Hall and Seebeck effects may have a limited ability for the determination of carrier concentration in complex thermoelectric PbTe-based and other multicomponent materials.

• Received 16 July 2013

DOI:https://doi.org/10.1103/PhysRevB.88.115211