dr. Graeme Blake (g.r.blake@rug.nl)

Organic-inorganic halide perovskites have attracted much attention as highly efficient absorbers in solar cells, as light emitters in optoelectronic devices, and in other emerging areas of application such as photodetectors, thermoelectric energy harvesting, magnetic cooling, and neuromorphic computing. In order to design new perovskites with specific properties and functionality, it is essential to understand their crystal structures in detail. They often exhibit a series of temperature or light-induced structural phase transitions driven both by features associated with the inorganic component and by orientational degrees of freedom of the organic molecules. This is often complicated by the presence of complex crystal twinning. We synthesise single crystal and polycrystalline halide perovskites and use X-ray diffraction techniques to obtain detailed knowledge of their crystal structures, leading to a better understanding of their optical, electronic and magnetic properties.

Figure 1. Crystal structure of (CH₃NH₃)PbI₃ at 200 K, showing four-fold disordered orientation of the methylammonium molecule and three-fold twinning of the crystal structure by rotation around the [201] direction. [1]

Joshua Levinsky

Magnetic skyrmions, swirling two-dimensional spin textures, are potential candidates for magnetic data storge applications such as racetrack memories, information carriers in spin-logic devices and artificial neurons or synapses in neuromorphic applications. We investigate various layered materials that have potential to stabilize magnetic skyrmions by means of magnetic frustration (for examples see this thesis). Theory predicts that skyrmions stabilised by magnetic frustration are not deflected to one side when moving through a material and can be an order of magnitude smaller, thus being advantageous for future applications involving the storage and manipulation of data. We utilise a variety of chemical synthesis techniques to obtain samples of various layered materials, and apply methods such as x-ray and neutron scattering and SQUID magnetometry to characterise their physical properties and search for signatures of this type of magnetic skyrmions.

Siebe van der Veer (s.van.der.veer@rug.nl)

Kisuma Chemicals and TNO are developing the STEPWISE technology, a Sorption-Enhanced Water-Gas-Shift technology for the reactive separation of CO₂ and H₂ from syngas sources. Kisuma produces the K/Mg/Al sorbent to reversibly adsorb the CO₂, although a sufficiently detailed description of the chemistry of the adsorption sites is lacking, as well as a description of the sorbent and its precursors. The materials are poorly crystalline and heterogeneous, which complicates their characterization. The goal of this project is the characterization of the K/Mg/Al sorbent material and its precursors.

Xin Feng (xin.feng@rug.nl)

Thermoelectric materials are of much current interest in the field of sustainable energy due to their potential in the conversion of waste heat to electrical power, as well as their use in solid-state cooling systems. The performance of thermoelectric materials can be expressed by the dimensionless “figure of merit”, ZT = α2T / ρκ. The general characteristics of a good thermoelectric material are a high Seebeck coefficient (α), low electrical resistivity (ρ) and low thermal conductivity (κ). The highest reported thermoelectric figures of merit are currently ~2.0 for bulk materials, while ZT > 3 is considered necessary for widespread commercial use. Our objective is to enhance the ZT of existing high-temperature thermoelectrics by controlling their nanostructures to minimise thermal conductivity, and by chemical doping to engineer their band structures.

Figure 1. Left: Cubic crystal structure of (GeTe)_x(AgSbTe2)_1-x at high temperature. The structure transforms to a rhombohedral phase (middle) on cooling, which gives rise to a complex nanostructure (right). This helps to lower the thermal conductivity, which is advantageous for a good thermoelectric material.

dr. Arkadeb Pal (arkadeb.pal@rug.nl)

Arkadeb's current research focuses on exploring new geometrically spin-frustrated magnets, including honeycomb, triangular, and Kagome spin lattices, and investigating their physical properties. He places special emphasis on exploring high critical temperature (T_c) magnetoelectric and magnetocaloric properties. Through the use of diffraction techniques such as neutron powder diffraction and synchrotron X-ray diffraction, coupled with Raman spectroscopy, he delves into the intricate relationship between these properties and the crystal structure, both globally and locally, in strongly correlated oxide systems. In addition to studying these magnets in their polycrystalline forms, Arkadeb also endeavors to grow high-quality single crystals and epitaxial thin films to explore the anisotropic aspects of these geometrically spin-frustrated systems.