Macro and Micro-Scale Features of Thermoelectric PbTe 
(Br, Na) Systems: Micro-FTIR Spectroscopy, Micro-Seebeck Measurements, and SEM/EDX Observations
In this work, n-type and p-type PbTe doped with Br and Na, respectively, were thoroughly examined to determine the effect of the dopant on microstructure. Macro and micro homogeneity of the samples were studied by means of micro-Fourier-transform infrared (micro-FTIR) spectroscopy, micro-Seebeck measurements, and scanning electron microscopy with energy-dispersive x-ray analysis (SEM/EDX). SEM/EDX observations showed the samples were not single-phase materials—second phases were created by inclusions that disturbed the coherence of the matrix and, subsequently, drastically affected the Seebeck coefficient. In a micro-scale study, local variations of sodium content were detected in Na-doped samples; in Br-doped samples a second, PbBr2, phase was observed in the PbTe matrix. A direct effect of matrix dopant on Seebeck coefficient and plasmon frequency for the Br-doped and Na-doped samples was observed by use of the three complementary techniques.