Atomic displacements in High-Entropy Alloys examined
The supercell is randomly filled with the five elements on the fcc-lattice positions; In the starting configuration, all layers are precisely on top of each other. The displacements of all elements in the final configuration have been revealed by a simultaneous fit of the independent experimental spectra with a use of Reverse Monte Carlo simulations. © A.Kuzmin / University of Latvia and A. Smekhova / HZB
High-entropy alloys of 3d metals have intriguing properties that are interesting for applications in the energy sector. An international team at BESSY II has now investigated the local order on an atomic scale in a so-called high-entropy Cantor alloy of chromium, manganese, iron, cobalt and nickel. The results from combined spectroscopic studies and statistical simulations expand the understanding of this group of materials.
High-entropy alloys are under discussion for very different applications: Some materials from this group are suitable for hydrogen storage, others for noble metal-free electrocatalysis, radiation shielding or as supercapacitors.
The microscopic structure of high-entropy alloys is very diverse and changeable; in particular, the local ordering and the presence of different secondary phases affect significantly the macroscopic properties such as hardness, corrosion resistance and also magnetism. The so-called Cantor alloy, which consists of the elements chromium, manganese, iron, cobalt and nickel mixed in an equimolar proportion, can be considered as a suitable model system for the whole class of these materials.
Local structure studied at BESSY II
Scientists from the Federal Institute for Materials Research (BAM, Berlin), the University of Latvia in Riga, Latvia, the Ruhr University in Bochum and the HZB have now studied the local structure of this model system in detail. Using X-ray absorption spectroscopy (EXAFS) at BESSY II, they were able to precisely track each individual element and their displacements from the ideal lattice positions for this system in the most unbiased manner with the help of statistical calculations and the reverse Monte Carlo method.
Chromium shows larger displacements
In this way, they uncovered peculiarities in the local environment of each element: Despite all five elements of the alloy are distributed at the nodes of the face-centred cubic lattice and have very close statistically averaged interatomic distances (2.54 - 2.55 Å) with their nearest neighbours, larger structural relaxations were found solely for chromium atoms. Besides, no evidence of secondary phases was detected at the atomic scale. The macroscopic magnetic properties studied with conventional magnetometry at HZB CoreLab were correlated with the revealed structural relaxations of Chromium.
"The results describe the arrangement of individual atoms at the atomic scale and how the complex magnetic order that we revealed may occur," explains HZB physicist Dr. Alevtina Smekhova, who supervised the experiments at HZB.
- Sodium-ion batteries: New storage mechanism for cathode materialsLi-ion and Na-ion batteries operate through a process called intercalation, where ions are stored and exchanged between two chemically different electrodes. In contrast, co-intercalation, a process in which both ions and solvent molecules are stored simultaneously, has traditionally been considered undesirable due to its tendency to cause rapid battery failure. Against this traditional view, an international research team led by Philipp Adelhelm has now demonstrated that co-intercalation can be a reversible and fast process for cathode materials in Na-ion batteries. The approach of jointly storing ions and solvents in cathode materials provides a new handle for the designing batteries with high efficiency and fast charging capabilities. The results are published in Nature Materials.
- 10 million euros in funding for UNITE – Startup Factory Berlin-BrandenburgUNITE – Startup Factory Berlin-Brandenburg has been recognised by the Federal Ministry for Economic Affairs and Energy as one of ten nationwide flagship projects for science-based start-ups. UNITE is to be established as a central transfer platform for technology-driven spin-offs from science and industry in the capital region. The Helmholtz Centre Berlin will also benefit from this.
- Helmholtz Doctoral Award for Hanna TrzesniowskiDuring her doctoral studies at the Helmholtz Centre Berlin, Hanna Trzesniowski conducted research on nickel-based electrocatalysts for water splitting. Her work contributes to a deeper understanding of alkaline water electrolysis and paves the way for the development of more efficient and stable catalysts. On 8 July 2025, she received the Helmholtz Doctoral Prize, which honours the best and most original doctoral theses in the Helmholtz Association.