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Research

The group’s research focuses on the synthesis, characterization and optimization of a broad range of solid-state compounds.

Materials

 

  • materials based on GeTe, PbTe, Ge/Sb/Te or Ge/Bi/Te with high thermoelectric performance
  • layered structures with intrinsic defects on various length scales
  • thermoelectric performance optimized by targeted doping
enlarge the image: Crystal structure, SEM and HRTEM image of MnBi2Te4 (Figure: Dr. C. Benndorf)
Crystal structure, SEM and HRTEM image of MnBi2Te4 (Figure: Dr. C. Benndorf)

  • mixed ionic-electronic conductors: Zn13-δSb10 , Cu2Se, and AgCrSe2 with high thermoelectric performance, but ionic conductivity leads to decomposition under electrical fields
  • X-ray diffraction computed tomography (3D-XRDCT) in situ
enlarge the image: Intensity of a Cu reflection in different layers of the sample (left) (Figure: Dr. C. Benndorf)
Intensity of a Cu reflection in different layers of the sample (left) (Figure: Dr. C. Benndorf)
enlarge the image: Crystal structure of Zn12.8-δSb10 and SEM images of deposited Zn (Figure: Dr. Benndorf)
Crystal structure of Zn12.8-δSb10 and SEM images of deposited Zn (Figure: Dr. Benndorf)

  • diverse structural chemistry of nitridic frameworks with condensed SiN4, PN4, Si(N,O)4 and P(N,O)4 tetrahedra
  • doping with Eu2+ or Ce3+ ⇒ luminescence materials for LEDs
enlarge the image: Excitation and photoluminescence spectra and crystal structure of (Lu/Y)Ba2[Si12O2N16C3]:Eu2+ with network of SiC(O/N)3 tetrahedra (Figure: Dr. C. Benndorf)
Excitation and photoluminescence spectra and crystal structure of (Lu/Y)Ba2[Si12O2N16C3]:Eu2+ with network of SiC(O/N)3 tetrahedra (Figure: Dr. C. Benndorf)
enlarge the image: Complex crystal structure of the oxonitridophosphate La21P40O46N57 with highlighted P(N,O)4 network (Figure: Dr. C. Benndorf)
Complex crystal structure of the oxonitridophosphate La21P40O46N57 with highlighted P(N,O)4 network (Figure: Dr. C. Benndorf)

Project of Dr. C. Benndorf

  • layered mixed-anionic compounds like RESbS and REBiTe with square-like arrangement of Sb and Bi atoms
  • CDWs examined by low-temperature diffraction, electron microscopy and spectroscopy
enlarge the image: Crystal structure of LaBiTe and electrical resistivity of NdBiTe indicating CDW formation at 150 K (Figure: Dr. C. Benndorf)
Crystal structure of LaBiTe and electrical resistivity of NdBiTe indicating CDW formation at 150 K (Figure: Dr. C. Benndorf)

  • stacking faults and diffuse scattering of BeP2 and BeAs2
  • structure determination by combination of synchrotron and electron diffraction, bonding analysis with DFT calculations
enlarge the image: Diffuse reflections and different stacking modes of layers of [As8]8- rings in BeAs2 (Figure: Dr. C. Benndorf)
Diffuse reflections and different stacking modes of layers of [As8]8- rings in BeAs2 (Figure: Dr. C. Benndorf)

Methods

  • SEM imaging and EDX spectroscopy ⇒ chemical analysis, microstructure of composite materials
  • HRTEM imaging and electron crystallography ⇒ structure determination of nanocrystals
enlarge the image: Scanning and Transmission Electron Microscopy (Figure: Dr. C. Benndorf)
Scanning and Transmission Electron Microscopy (Figure: Dr. C. Benndorf)

  • single-crystal and powder diffraction
  • micro-focused synchrotron beams ⇒ micro-/nano-crystals
  • diffuse scattering, resonant diffraction, and more…
enlarge the image: Single-crystal diffraction at ESRF, Grenoble (left) and at DESY, Hamburg (right) (Figure: Dr. C. Benndorf)
Single-crystal diffraction at ESRF, Grenoble (left) and at DESY, Hamburg (right) (Figure: Dr. C. Benndorf)

  • modern solid-state synthesis
    • high-temperatures
    • inert conditions
    • melt-spinning and high-frequency induction
    • chemical vapor transport
    • hydrothermal conditions
    • flux-assisted synthesis
    • …
enlarge the image: Examples of our synthesis (Figure: Dr. C. Benndorf)
Examples of our synthesis (Figure: Dr. C. Benndorf)

  • electrical conductivity and Seebeck coefficient (LSR)
  • thermal conductivity and heat capacity (LFA)
enlarge the image: LFA and LSR (Figure: Dr. C. Benndorf)
LFA and LSR (Figure: Dr. C. Benndorf)

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