High-Pressure Synthesis of β-Ir₄B₅and Determination of the Compressibility of Various Iridium Borides

Abstract

A new iridium boride, β-Ir4B5, was synthesized under high-pressure/high-temperature conditions of 10.5 GPa and 1500 °C in a multianvil press with a Walker-type module. The new modification β-Ir4B5 crystallizes in a new structure type in the orthorhombic space group Pnma (no. 62) with the lattice parameters a = 10.772(2) Å, b = 2.844(1) Å, and c = 6.052(2) Å with R1 = 0.0286, wR2 = 0.0642 (all data), and Z = 2. The structure was determined by single-crystal X-ray and neutron powder diffraction on samples enriched in 11B. The compound is built up by an alternating stacking of boron and iridium layers with the sequence ABA′B′. Additionally, microcalorimetry, hardness, and compressibility measurements of the binary iridium borides α-Ir4B5, β-Ir4B5, Ir5B4, hexagonal Ir4B3–x and orthorhombic Ir4B3–x were carried out and theoretical investigations based on density function theory (DFT) were employed to complement a comprehensive evaluation of structure–property relations. The incorporation of boron into the structures does not enhance the compressibility but leads to a significant reduction of the bulk moduli and elastic constants in comparison to elemental iridium.

Crystal Structure and Physical Properties of the Cage Compound Hf2B2–2δIr5+δ

“…The binary iridium boron system has been studied thoroughly, 36 , 37 and recent attention is mainly due to joint theoretical and experimental classification of some iridium borides as potentially superhard materials. 38 − 40 …”

“…Also, platinum metals and their interaction with boron have been the targets of investigation, − which have been directed toward an understanding of their distinct structural chemistry and/or exploration of their mechanical properties. The binary iridium boron system has been studied thoroughly, , and recent attention is mainly due to joint theoretical and experimental classification of some iridium borides as potentially superhard materials. − …”

The crystal structures, phase stabilities, electronic structures and bonding features of iridium borides from first-principles calculations

“…57 Besides the 1D B-ribbons, we also found the graphene-like B-sheet with short sides of 1.89 A and long sides of 2.00 A in Cm-Ir 4 B 5 , which is shorter than the high-pressure synthesis of b-Ir 4 B 5 (2.122 A). 58 In general, it is worth noting that the distances of the nearest neighbor Ir-B bonds in these six considered structures are all smaller than the sum (2.25 A) of the covalent radii of the B atom (rB ¼ 0.84 A) and the Ir atom (rIr ¼ 1.41 A), demonstrating the strong covalent bonding between Ir and B in these six considered phases. However, with increasing B concentration, the number of Ir-B covalent bonds decreases, and strong B-B covalent bonds gradually appear for borides with 1 < B/Ir < 2.…”

“… 57 Besides the 1D B-ribbons, we also found the graphene-like B-sheet with short sides of 1.89 Å and long sides of 2.00 Å in Cm -Ir 4 B 5 , which is shorter than the high-pressure synthesis of β-Ir 4 B 5 (2.122 Å). 58 …”

Synthesis, crystal structure, and properties of stoichiometric hard tungsten tetraboride, WB4

“…Inexpensive hard and superhard (with a Vickers hardness of around 40 GPa and above) materials are in much demand for various industrial applications. Novel carbides, 1 nitrides, [2][3][4][5][6][7][8] borides, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and other compounds of transition metals, 24,25 which can potentially combine high hardness and promising optical, electronic, and other properties, are the focus of extensive investigations. [26][27][28] Nowadays, one of the most widely used hard materials for commercial applications is tungsten carbide, WC.…”