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.
Isolde Zeiringer程曦月陈星秋Ernest BauerGerald GiesterPeter Franz Rogl
The Mechanical properties of the hexagonal tungsten nanowhiskers, which were synthesized by chemical vapor deposition, were characterized by instrumented nanoindentation and atomic force microscope （AFM）. The nanoindentation results show that tungsten nanowhiskers exhibit a hardness of （6.2±1.7） GPa and an elastic modulus of （225±20） GPa. According to the comparative test results, the tungsten nanowhiskers possess a comparable hardness to tungsten microwhiskers, and an hardness increase of 35% to the bulk single-crystal tungsten. The increase in the hardness of whiskers is attributed to the lacking of dislocation avalanche observed in the bulk single-crystal tungsten. The measured modulus is about 80% that of the tungsten microwhiskers, which can be contributed to the size effects of the nanowhiskers and the substrate effects in the nanoindentation test.
