Ternary Borides of the Zr–Ir–B System: Composition, Crystal Structure, and Properties

Ternary transition metal borides exhibit a wide variety of crystal structures and, as a consequence, a wide range of functional properties. This work investigates ternary phases formed via the interaction of zirconium diboride with iridium. The analysis of powder XRD, SEM, and WDS indicates the formation of three known ternary boride phases (Zr₂Ir₆B, ZrIr₃B₄, and Zr₂Ir₅B₂) and two novel phases (ZrIr₇B₂ and ZrIr₂B). In the wide range of reagents' mixture compositions, the main products are Zr₂Ir₅B₂ and ZrIr₂B; in the 4-fold excess of iridium, the composition of products changes to a mixture of Zr₂Ir₆B and ZrIr₇B₂. The structure of the novel phase, ZrIr₇B₂, was studied with single-crystal X-ray diffraction and powder time-of-flight neutron diffraction, which showed that it crystallizes in a new structure type with a layered hexagonal structure P6̅2m: a = 5.5683(7) Å, c = 5.6058(7) Å. The structure consists of Kagomé net layers formed by [BIr₆] trigonal prisms, with Zr atoms in the free space of each layer and Ir atoms in the interlayer space. Additionally, the Vickers microhardness of the ternary borides was measured; all ternary compounds display microhardness in the range of 15-19 GPa.