High-Pressure X-ray Diffraction

The investigation of crystalline matter under high pressures has been focus of many research studies from mineralogists, physicists and chemists. The fascination of pressure as stimulus is nicely illustrated when looking at some research examples: in a recent breakthrough discovery near room temperature superconductivity has been observed under high pressures. Likewise, it is an established theory that all crystalline matter becomes metallic at pressures high enough, a viewpoint that has kept researchers searching for metallic hydrogen until today.

When considering the behaviour of coordination polymers as a function of pressure, it is important to note that many coordination polymers can be considered as soft materials. Additionally, phase transitions and amorphisation processes can occur at pressures below p < 0.1 GPa, thereby challenging established high-pressure X-ray diffraction setups such as Diamond Anvil Cells (DACs). Therefore, in addition to DACs, we apply a custom-made powder X-ray diffraction setup for probing the response of soft materials in the pressure range between p = ambient – 0.4 GPa. On-going research projects in the group focus on both soft and mechanically robust coordination polymers. Goal is the identification of structural and compositional factors that help us in the manipulation of the underlying free energy landscape and in turn the mechanical response in general.

Figure 1. Results of high-pressure powder X-ray diffraction on ZIF-4(Zn). (a) Contour plot of high-pressure powder X-ray diffraction pattern of ZIF-4(Zn) with a phase transition visible at around p = 0.075 GPa. In (b) the volume as a function of pressure is given, whilst in (c) the development of the lattice parameters as a function are shown. Lattice parameters and volume have been extracted via a Pawley profile fit. Figure modified from G. Kieslich et al. Z. Allgm. Anorg. Chem. 2019, 645, 970.

Some related publications:
  • P. Vervoorts, C. L. Hobday, M. G. Ehrenreich, D. Daisenberger, G. Kieslich. The Zeolitic Imidazolate Framework ZIF-4 under Low Hydrostatic Pressures. Z. Anorg. Allg. Chem. 2019, 645, 970-974.
  • S. Dissegna, P. Vervoorts, C. L. Hobday, T. Düren, D. Daisenberger, A. J. Smith, R. A. Fischer*, G. Kieslich*. Tuning the Mechanical Response of Metal-Organic Frameworks by Defect-Engineering. J. Am. Chem. Soc. 2018, 140, 11581.