Crystal structures and constitution of the binary system iridium-boron

铱硼二元系相及晶体结构的澄清（英文）

The constitution of the binary system Ir-B has been established between 10 and 70 at.% boron for temperatures above 700°C based on differential scanning calorimetry, electron probe microanalysis, and isothermal low temperature annealing experiments(≤1000°C). Four binary phases have been found, namely Ir4B5+x, Ir5B4+x and the high and low temperature modification of Ir4B3-x. X-ray structure analyses were performed on single crystals of Ir4B5+x(x = 0, Ir4B5 type; space group C2/m; a = 1.05200(2), b = 0.289564(6) and c = 0.60958(1) nm, β = 91.156(2)°), Ir5B4+x(x=0, Ir5B4 type; space group I41/a; a = 0.62777(1) and b = 1.02599(2) nm) and on the low temperature modification of Ir4B3-x(x=0, Ir B0.9 type; space group Cmc21; a = 0.27728(1), b = 0.75742(2) and c = 0.73152(2) nm). The high temperature modification of Ir4B3-x(WC type; space group P6-m2; a = 0.28137(5) and c = 0.2828(1) nm) has been confirmed by X-ray powder diffraction. By means of the first-principle calculations, in combination with the evolutionary structural search algorithm, the compositions, structures and enthalpies of the Ir-B system have been investigated theoretically. Confirming the experimental observations on Ir4B5, Ir5B4 and Ir4B3, we have investigated several metastable phases at other stoichiometries, such as Ir B, Ir B2 and Ir3B2. We also proposed three thermodynamically and dynamically stable new structures of o F28-Ir4B3, o C8-Ir B and m C10-Ir3B2, which may be synthesized under certain conditions.

本文通过差示扫描量热法、电子探针以及等温低温退火处理,系统地研究了铱硼二元体系在B元素含量10%~70%范围内化合物的结构及组成,并成功的合成及表征了四种化合物:Ir4B5+x,Ir5B4+x以及Ir4B3-x的高温和低温相.运用单晶X射线衍射法确定了Ir4B5+x(x=0,Ir4B5型;空间群C2/m;a=1.05200(2),b=0.289564(6),c=0.60958(1)nm,β=91.156(2)°),Ir5B4+x(x=0,Ir5B4型;空间群I41/a;a=0.62777(1),b=1.02599(2)nm)以及Ir4B3-x低温相(x=0,Ir B0.9型;空间群Cmc21;a=0.27728(1),b=0.75742(2),c=0.73152(2)nm)的晶格常数及结构.运用粉末X射线衍射法确定了Ir4B3-x高温相(WC型;空间群P6-m2;a=0.28137(5),c=0.2828(1)nm)的晶格常数及结构.通过第一性原理计算结合结构演化搜索方法,从理论上研究了该体系的组成、结构以及相稳定性.除了验证实验合成的Ir4B5、Ir5B4以及Ir4B3,本文还预测了三个可能在一定条件下合成的新稳定结构:o F28-Ir4B3,o C8-Ir B以及m C10-Ir3B2.