Phase relationship and superconductivity in the Bi-rich part of the binary system Rh–Bi

The bismuth-rich part of the binary Rh–Bi system was re-investigated applying high-temperature centrifugation, DTA/DSC measurements and X-ray single-crystal and powder diffraction techniques. The obtained results allow understanding of some contradictorily looking observations reported in the literature. Two modifications of RhBi2, RhBi3 and RhBi4 are the stable phases. The tetrabismuthide RhBi4 forms in a peritectic reaction from melt and β-RhBi2 at 466 ∘C. The tribismuthide RhBi3 forms peritectoidically in a reaction between β-RhBi2 and RhBi4 at 433 ∘C and decomposes eutectoidally at 336 ∘C into α-RhBi2 and RhBi4. The dibismutide RhBi2 reveals two modifications: the monoclinic α-RhBi2 exists below 370 ∘C, and the triclinic β-RhBi2 was found above 370 ∘C. The newly found bismuth-rich phase Rh3Bi14 is formed as a metastable one in absence of RhBi4 nuclei and transforms to RhBi4+Bi even below the eutectic with an exothermic reaction. RhBi4 and Rh3Bi14 reveal superconductivity with the transition temperatures of 2.82 and 3.15 K, respectively.