New Study on Spinel Oxides Published
Iron-aluminium ratio determines functional properties – important findings for zinc batteries and materials design
01 July 2026 – A research team at Helmholtz Institute Münster (HI MS) at Forschungszentrum Jülich has gained new insights into zinc-conducting spinel oxides. In their latest publication, the researchers demonstrate how functional material properties can be specifically tailored via the chemical composition.
Adjustable Properties Through Mixed-Crystal Formation
The work focuses on the so-called mixed-crystal series between zinc ferrite (ZnFe₂O₄, also known as the mineral franklinite) and zinc aluminate (ZnAl₂O₄, gahnite). The study shows that iron (Fe) and aluminium (Al) can completely substitute for one another in the crystal structure without fundamentally altering it.
In the process, the properties of the materials change systematically with the Fe/Al ratio: as the aluminium content increases, both electrical and electronic conductivity as well as magnetic susceptibility decrease, whilst the optical bandgap increases.
Investigations at the material and cellular level also demonstrate reversible insertion of zinc ions (Zn²⁺) and protons – an important indication of the potential of these materials for electrochemical energy storage.
Contribution to the Understanding of Zinc Batteries
Zinc-based battery systems are regarded as a promising option for stationary energy storage – partly due to the availability of raw materials, established recycling infrastructure and the possibility of using aqueous, non-flammable electrolytes.
However, challenges remain, such as the stability of electrode materials in aqueous electrolytes. This study provides important insights in this regard: it demonstrates how the properties of spinel materials can be influenced by specifically varying their composition.
The results can contribute in particular to the further development of more complex material systems such as zinc-manganese-iron-aluminium oxide and help to better address existing problems – such as the limited stability of cathode materials.
Basic Research With Broad Relevance
In addition to their application in batteries, the findings are also relevant to other fields, such as geoscientific questions concerning the corresponding ore minerals.
Furthermore, the investigations show that zinc-iron oxide exhibits electronic conductivity dependent on the partial pressure of oxygen at temperatures above 600 °C – an indication of possible additional oxygen ion conductivity.
Interdisciplinary Collaboration
The study was conducted in close collaboration between Helmholtz Institute Münster (IMD-4) and the Institute for Energy and Climate Research (IET-1) at Forschungszentrum Jülich, as well as FH Münster and other partners.
It combined experimental materials development, electrochemical characterisation and structural analysis methods such as X-ray and neutron scattering. Supplementary investigations into optical and magnetic properties furthered the understanding of the functional relationships.
Study Published in the Journal Solid State Ionics
The researchers published the detailed results of their study as an open-access article in the journal Solid State Ionics.
Researchers Involved:
• Meriem Machitouen – Helmholtz Institute Münster at Forschungszentrum Jülich and FH Münster
• Patrick Mowe – Helmholtz Institute Münster
• Johannes Spiegel – Institute for Energy and Climate Research (IET-1) at Forschungszentrum Jülich
• Susanna Krämer – Helmholtz Institute Münster
• Prof. Dr Rüdiger-A. Eichel – IET-1 und RWTH Aachen University
• Prof. Dr Martin Winter – Helmholtz Institute Münster and MEET Battery Research Center at University of Münster
• Prof. Dr Thomas Jüstel – FH Münster
• Dr Anna Windmüller – IET-1
• Dr Kerstin Neuhaus – Helmholtz Institute Münster