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Boron rich transition metal borides are known as potential candidates for hard and incompressible materials. Two structural modifications of compound from this category of alloys, α- and β-Ir2B3-x (formerly denoted as Ir4B5) have been synthesized. α-Ir2B3-x crystallizes in C2/m space group (x=0.54, a=10.5515(11) Å, b=2.8842(3) Å, c=6.0965(7) Å, β =91.121(9)º). The α-Ir2B3-x is built of corrugated layers of boron hexagons alternated along c-direction with two corrugated layers of iridium. The boron layer in α-Ir2B3-x is similar to the ReB2 boron substructure owing to chair configuration of boron hexagons, however differs from the latter structure by mode of condensation of B6 units via external B-B bond realizing the formation of distorted quadrilaterial zigzag boron ribbons. The boron substructure in β-Ir2B3-x is composed of ribbons built up of slightly corrugated quadrilaterial units resulted from linkage of two parallel boron chains via external B-B bond of each chain. Geometrically, the unit cell of β-Ir2B3-x consists of two blocks composed of an 8-membered iridium cage encapsulating the boron ribbon and columns of boron half-filled iridium trigonal prisms [B3Ir6] running along b; the blocks are mutually shifted along the a-direction for a half a unit cell.
DFT calculations revealed a number of bands crossing the Fermi level predicting metallic behaviors of the two compounds. β-Ir2B3-x is characterized by a pseudogap around the Fermi level and a small eDOS of 0.6405 states/eV*f.u. on the Fermi level.
As compared to α-Ir2B3-x, the ELF calculations for β-Ir2B3-x indicated strong interaction between iridium and boron, however, demonstrated a negligible covalent bonding component within the quadrilaterial boron substructure thus explaining the reduced hardness of β-Ir2B3-x. Current structural studies combined with DFT calculation and bonding analysis proved the role of chemical bonds within boron layers as well as between metal layer and boron layer in determining the hardness of transition metal borides.

権利情報:

• In Copyright
  

キーワード: boride

刊行年月日: 2024-08-27

出版者: Royal Society of Chemistry (RSC)

掲載誌:

• Dalton Transactions (ISSN: 14779226) vol. 53 issue. 38 p. 15859-15871

研究助成金:

• Austrian Science Fund P31979-N36
• Austrian Science Fund P35945-N
• Hrvatska Zaklada za Znanost IP-2022-10-3382
• Japan Science and Technology Agency JPMJMI19A1

原稿種別: 査読前原稿 (Author's original)

MDR DOI: https://doi.org/10.48505/nims.4817

公開URL: https://doi.org/10.1039/d4dt02095b

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更新時刻: 2024-10-09 08:31:06 +0900

MDRでの公開時刻: 2024-10-09 08:31:06 +0900