Pb0.7Ge0.3Te and Pb0.5Ge0.5Te alloys, (i) quenched from 923 K or (ii) quenched and annealed at 573 K for
2 h, have been studied by 125 Te NMR, X-ray diffraction, electron and optical microscopy, as well as energy
dispersive spectroscopy. Depending on the composition and thermal treatment history, 125
Te NMR spectra exhibit different resonance frequencies and spin-lattice relaxation times, which can be assigned
to different phases in the alloy. Quenched and annealed Pb0.7Ge0.3Te alloys can be considered as
solid solutions but are shown by NMR to have components with various carrier concentrations.
Quenched and annealed Pb0.5Ge0.5Te alloys contain GeTe- and PbTe-based phases with different
compositions and charge carrier concentrations. Based on the analysis of non-exponential 125
Te NMR spin-lattice relaxation, the fractions and carrier concentrations of the various phases have been
estimated. Our data show that alloying of PbTe with Ge results in the formation of chemically and
electronically inhomogeneous systems. 125
Te NMR can be used as an efficient probe to detect the local
composition in equilibrium as well as non-equilibrium states, and to determine the local carrier
concentrations in complex multiphase tellurides.