Novel europium and uranium carbides produced by flux synthesis

• Applicant: Professor Dr. Uwe Ruschewitz
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574743669

In the proposed project, novel europium and uranium carbides will be synthesized and initially characterized structurally. This will be followed by a detailed investigation of the properties of these compounds. In addition to structural and magnetic phase transitions, we also expect interesting valence changes for both classes of compounds. These are also known for ytterbium carbides, which we have already been investigated in an earlier project, so that they will only play a minor role in this proposal. The synthesis of thorium carbides is a fourth subproject, but these are mainly intended to serve as hosts for uranium in order to specifically simplify the sometimes complex magnetic properties through dilution. In addition to the properties mentioned above, we hope to observe exciting magnetoresistance effects in europium carbides (e.g., CMR, as already investigated by us in EuC2) or even unconventional superconductivity, as recently found in UTe2. We have already achieved a first success in synthesizing Eu2Li(C3)H and U2TeC2 in flux, so this approach to growing single crystals will be the focus of the project. Eu2Li(C3)H is a ferromagnet with a surprisingly high transition temperature Tc = 42 K, while U2TeC2 exhibits the expected complex magnetic behavior with a ferromagnetic ground state, but no superconductivity is found up to 2 K. In the proposed project, we now want to synthesize further europium carbides in order to investigate their properties in a targeted manner. The successful syntheses of Eu12GaC13-x and Eu12InC13-x are the first results on this path, but we currently have no information about their properties. In the field of uranium carbides, we first want to specifically produce “doped” UxTh2-xTeC2 in order to decipher the magnetic properties of U4+ in these compounds through dilution. Since we have already been able to produce U2SbC2—with a structure similar to but not identical to U2TeC2—there is the interesting possibility of “doping” electrons into these compounds. We will investigate whether these electrons lead to a charge distribution according to U4+U5+ - Sb3– - C26– or (U4+)2 – Sb3– - C25–. To our knowledge, such investigations have not yet been carried out (not even on similar systems). A final subproject will focus on the methodological development of flux syntheses under high-pressure conditions (up to approx. 15 GPa). There is virtually no preliminary work available for preparative applications in this area. However, there are indications that flux can significantly lower the activation barriers for reactions, so that in our Large Volume Press (LVP) with maximum pressures of up to approx. 15 GPa, it may be possible to synthesize novel compounds that are otherwise only possible in diamond anvil cells (DAC) at significantly higher pressures. Here, we hope in particular to synthesize polycarbides in mg quantities.

• DFG Programme: Research Grants