Crystal Growth of Inter-Metallic Rhodium Compounds

Our previous results on the RhPb₂ intermetallic compound [1] inspired us to search for new Rh compounds that may have topological and superconducting properties. Preliminary investigation of them in the ternary Au-Rh-Pb phase diagram has shown that AuPb₄Rh₅ exists newly [2]. Moreover, resistivity measurements of the grown crystals that had a chemical composition close to AuPb₃Rh₃ (EPMA results) have shown two superconducting transitions at 1.73 K and 2.8 K, which do not correspond to the transition temperatures of superconductors from the binary Au-Pb and Rh-Pb phase diagrams.<br/><br/>Further investigation of the ternary phase diagram yielded unexpected results. The EPMA measurements of grown crystals with an infrared mirror furnace similar to RhPb₂ [1] having the initial molar ratio of Au:Pb:Rh=1:4:1 showed that the crystals are Rh₂Pb₃, which seems not to exist to our knowledge or in the known binary Rh-Pb phase diagram [3]. This implies that the current understanding of the binary Rh-Pb phase diagram is incomplete.<br/><br/>During the RhPb₂ melting experiments[1], it was noted that Fe does react with the Rh-Pb alloy, indicating that some compounds might form. This inspired us to investigate further other phase diagrams as well. The melting experiments with a muffle furnace have shown that square-plate-like crystals can grow on the surface of the boule from the melt with an initial molar ratio of Au:Fe:Rh:Pb=2:2:1:4. Surprisingly, the EPMA measurements have shown that the grown crystals do not contain Au and Pb and it turns out finally to be FeRh. To our knowledge, this is the first time that single crystals of FeRh are grown from the melted flux of Au and Pb. The inter-metallic FeRh compound has been studied in the past intensively on peculiar ferromagnetic to antiferromagnetic transition, anomalous thermodynamical properties, crystal structural transformation, <i>etc</i>. near the stoichiometric 1:1 composition of Fe and Rh. However, the lack of a good single crystal has hindered understanding of these interesting properties of the RhFe intermetallic compound.The single crystal made by our method will <br/>enaible us to uderstand more deeply the intruging RhFe intermetallic compound.<br/><br/>[1] N.Subotić,<i> etc. </i>MRS Advances (2022) https://doi.org/10.1557/s43580-022-00292-5.<br/>[2] N.Subotić,<i> etc. </i>to be published<br/>[3] <i>“Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloy, Pb-Rh (Lead-Rhodium)"</i>, Landolt-Börnstein -Group IV Physical Chemistry <b>5I </b>(1998) 321.