Phase stability and possible superconductivity of new 4d and 5d transition metal high-entropy alloys

We report the synthesis of new equimolar high-entropy alloys formed from five or six 4d/5d transition metals that are each from a different Group of the Periodic Table. These include MoReRuRhPt and MoReRuIrPt, which appear to crystallise as single hexagonal close-packed phases and so are isostructural and isoelectronic to the high-pressure phase of the well-known high-entropy alloy CrMnFeCoNi. Other compositions crystallise as mixed phases, which we rationalise using the atomic size difference, delta, and the electronegativity difference, Delta chi, of the constituent elements. Finally, we find signs of superconductivity in eight of these new systems.