Four alloys of Pb0.7Ge0.3Te and Pb0.5Ge0.5Te initial compositions,
quenched from 923 K or quenched and annealed at 573 K for 2 h,
have been studied using X-ray diffraction,125
Te NMR, optical andelectron microscopy, and energy dispersive spectroscopy.125 TeNMR spectra of both quenched and annealed Pb0.7Ge0.3Te alloys show a signal peak at 1510 ppm with 70 kHz width, indicating
formation of solid solutions in both alloys. Biexponential spinlattice relaxation is found for both alloys, showing that they
contain regions with different charge carrier concentrations due to variation in the local composition. In contrast,
125 Te NMR of Pb0.5Ge0.5Te alloys shows two peaks, which can be attributed to
GeTe- and PbTe-based phases. The carrier concentration in the GeTe-based phase is high and uniform while the PbTe-based phase is electronically inhomogeneous. Similarly, 125 Te NMR of the annealed Pb0.5Ge0.5Te alloy also shows two peaks, which have different signal shapes due to a variation in the local environment of Te.125 Te NMR confirms X-ray diffraction and microstructure data showing phase separation in both Pb0.5Ge0.5Te alloys. Replacement of Pb by Ge in PbTe results in formation of chemically and electronically inhomogeneous systems. Our study highlights that
125 Te NMR can be used to detect and identify the local composition and carrier concentration in various phases of complex single- and multiphase thermoelectric tellurides.