Struktur-Eigenschafts-Beziehungen fehlgeordneter Sulfosalz-analoger multinärer (Ag,Cu)-(Pb,Sn)-(Sb,Bi)-Chalkogenide

• Antragsteller: Professor Dr. Oliver Oeckler
• Fachliche Zuordnung: Mineralogie, Petrologie und Geochemie
• Förderung: Förderung seit 2013
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 236935515

Based on the crystal chemistry of complex chalcogenides, in part inspired by natural sulfosalts, the synthesis and the understanding of structure-property relationships of new compounds in the system (Pb,Ag)-(Sb,Bi)-(S,Se,Te) shall lead to materials with promising (thermo-)electrical properties. In particular, real-structure effects on various length scales can be expected in metastable phases which are accessible by quenching and subsequent systematic annealing. The properties of such compounds can be tuned by substitution, both in terms of doping or of the partial or complete formation of solid solutions, as well as by metal atom ordering and the resulting domain formation. Kinetically controlled phase transitions or exsolution phenomena, which occur only partially, shall yield a simple route to bulk material with complex (preferably hierarchical) nanostructures.Starting from compounds in the system PbS/Bi2S3/Sb2S3, which are to be synthesized by conventional solid-state synthesis and by chemical transport reactions or sublimation, respectively, we also expect halogen-containing compounds, especially novel ones with bromine. Metal-atom ordering, block disorder and systems that are heterogeneous on the nanoscale provide a broad spectrum of structures and properties. The heterovalent substitution 2Pb2+ --> Ag+ + Bi3+ leads to additional variants. The integration of selenium and/or tellurium should lead to complex structures with combinations of chain-like and layer-like building blocks. Particularly, structural changes in the systems Pb2Bi2(S,Se)5 or Pb2(Sb,Bi)2Se5 indicate that metastable mixed phases may exist. The corresponding tellurides exhibit a more pronounced tendency towards layered compounds and a markedly increased metallic character.The methodical approach of this project focuses on transmission electron microscopy and electron diffraction for the elucidation of real-structure effects and consequently as a basis for the understanding of the properties. In combination with X-ray spectroscopy (EDX), these methods also allow us to analyze complex mixtures and identify new phases. Microfocus diffraction using synchrotron radiation will be used as a versatile tool to accurately determine their structures. In order to distinguish elements with similar atomic numbers, resonant diffraction will be used. Measurements of the charge carrier concentration, the bandgap, the Seebeck coefficient and the electrical and thermal conductivities will demonstrate the effects of the structural changes induced by substitution as well as the effects of metal-atom (or anion) ordering and changing metallic character.

• DFG-Verfahren: Sachbeihilfen