RESUMO
Understanding the mechanisms that connect heat and electron transport with crystal structures and defect chemistry is fundamental to develop materials with thermoelectric properties. In this work, we synthesized a series of self-doped compounds Cu2+x Mn1-x GeS4 through Cu for Mn substitution. Using a combination of powder X-ray diffraction, high resolution transmission electron microscopy and precession-assisted electron diffraction tomography, we evidence that the materials are composed of interconnected enargite- and stannite-type structures, via the formation of nanodomains with a high density of coherent interfaces. By combining experiments with ab initio electron and phonon calculations, we discuss the structure-thermoelectric properties relationships and clarify the interesting crystal chemistry in this system. We demonstrate that excess Cu+ substituted for Mn2+ dopes holes into the top of the valence band, leading to a remarkable enhancement of the power factor and figure of merit ZT.
RESUMO
Synopsis Oxidation hair dyes as raw materials may present toxic impurities from synthesis or degradation pathways, which are responsible for allergic phenomena. In the present study selective and sensitive HPLC methods are proposed for the determination of Bandrowski base, 4-chloroaniline, 1,2-phenylenediamine and 4,4'-diaminoazobenzene in 1,4-phenylenediamine as well as 2,4-diaminoanisole in N-hydroxyethyl-4-methoxy-1,3-phenylenediamine. The proposed methods, based on reversed phase mode separation using 1,8-diaminooctane as amine modifier and photodiode array detection, proved to be suitable for the purity assessment of these widely used hair dyes; in particular the cited potential impurities were determined at ppm level.
