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.

三元过渡金属硼化物具有丰富多样的晶体结构，因此也展现出宽泛的功能特性谱系。本研究针对二硼化锆与铱相互反应生成的三元物相展开探究。通过粉末X射线衍射（powder XRD）、扫描电子显微镜（Scanning Electron Microscope, SEM）以及波长色散光谱法（Wavelength Dispersive Spectroscopy, WDS）的分析结果表明，反应生成了三种已知三元硼化物物相（Zr2Ir6B、ZrIr3B4与Zr2Ir5B2）以及两种新型物相（ZrIr7B2与ZrIr2B）。在宽泛的反应物配料比范围内，主产物为Zr2Ir5B2与ZrIr2B；当铱过量至原计量比的4倍时，产物组成转变为Zr2Ir6B与ZrIr7B2的混合物。新型物相ZrIr7B2的结构通过单晶X射线衍射与粉末飞行时间中子衍射（time-of-flight neutron diffraction）展开解析，结果显示其以全新结构类型结晶，为层状六方结构，空间群为P6̄2m，晶胞参数a = 5.5683(7) Å，c = 5.6058(7) Å。该结构由[BIr6]三角棱柱构筑的卡戈美（Kagomé）网格层构成，每层的空隙中分布有锆原子，层间区域则填充有铱原子。此外，本研究还测定了各三元硼化物的维氏显微硬度，所有三元化合物的显微硬度均处于15~19 GPa区间内。