High-Pressure Synthesis of ß-Ir4B5 and Determination of the Compressibility of Various Iridium Borides.

A new iridium boride, ß-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 ß-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, ß-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.

Synthesis, Crystal Structure, and Compressibilities of Mn3-x Ir5 B2+x (0≤x≤0.5) and Mn2 IrB2.

The new ternary transition metal borides Mn3-x Ir5 B2+x (0≤x≤0.5) and Mn2 IrB2 were synthesized from the elements under high temperature and high-pressure/high-temperature conditions. Both phases can be synthesized as powder samples in a radio-frequency furnace in argon atmosphere. High-pressure/high-temperature conditions were used to grow single-crystals. The phases represent the first ternary compounds within the system Mn-Ir-B. Mn3-x Ir5 B2+x (0≤x≤0.5) crystallizes in the Ti3 Co5 B2 structure type (P4/mbm; no. 127) with parameters a=9.332(1), c=2.896(2) Å, and Z=2. Mn2 IrB2 crystallizes in the ß-Cr2 IrB2 crystal structure type (Cmcm; no. 63) with parameters a=3.135(3), b=9.859(5), c=13.220(3) Å, and Z=8. The compositions of both compounds were confirmed by EDX measurements and the compressibility was determined experimentally for Mn3-x Ir5 B2+x and by DFT calculations for Mn2 IrB2 .