Oxidation of intermetallic aluminum compounds for the synthesis of (new) chalcogenides

• Applicant: Privatdozent Dr. Oliver Janka
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 577884074

This project deals with the oxidation of intermetallic aluminum compounds. The goal is hereby to synthesize known and new oxides, sulfides, selenides, and tellurides. To this end, intermetallic aluminum compounds known to literature are synthesized at first. The synthesis is usually carried out from the elements by means of arc-melting or in refractory metal ampoules. The precursor compounds obtained are then characterized by powder diffractometry and, if not already done, by 27Al solid-state NMR spectroscopy. Oxidation takes place in a second step in a flow furnace, which can be gassed with oxygen, humid argon, or ozone. In the case of oxidation with the heavier homologues sulfur, selenium, or tellurium, fused silica glass ampoules can be used. After successful preparation of the chalcogenides, they will also be examined using diffraction and various spectroscopy methods (NMR, IR, Raman, etc.). The project distinguishes between compounds that have defined oxidation states in their oxidized form and those in which one of the metals can have several oxidation states. While the reactions in the first case should proceed clearly, the second part aims to achieve a specific oxidation state. One example is the oxidation of EuAl2 with oxygen. This can lead to the formation of divalent and trivalent europium. If the compound is oxidized in an excess of oxygen, only Eu3+ is found, whereas divalent europium can be obtained with stoichiometric amounts of O2. Another aspect is the investigation of the corresponding reaction mechanisms. In the case of the oxidation of CaAl2, it was shown that CaAl2O4 does not form directly as expected, but rather a calcium-richer oxide (Ca12Al14O33). It subsequently became clear that calcium diffuses to the surface during oxidation and there forms the aforementioned oxide. Once all metallic components have reacted, a classic diffusion-controlled ceramic reaction occurs, ultimately forming the CaAl2O4 mentioned at the beginning. However, ball-milling the starting material had a drastic effect on the reaction mechanism. Defect-rich CaAl2 directly forms CaAl2O4 in very high quantities, while the formation of Ca12Al14O33 is suppressed. Therefore, in addition to investigating the reaction mechanisms, the mechanochemical treatment of the starting materials and the resulting change in the reaction mechanism will also be studied.

• DFG Programme: Research Grants