Crystal Structure of W1-x B-3 and Phase Equilibria in the Boron-Rich Part of the Systems Mo-Rh-B and W-{Ru,Os,Rh,Ir,Ni,Pd,Pt}-B

Author(s)
I. Zeiringer, P. Rogl, A. Grytsiv, Julia Polt, E. Bauer, G. Giester
Abstract

The crystal structure of W

1-x B

3 has been reinvestigated by x-ray single crystal diffraction and revealed isotypism with the Mo

1-x B

3 structure type (space group P6

3/mmc; a = 0.52012(1), c = 0.63315(3) nm; R

F = 0.040). As a characteristic feature of the structure, planar hexagonal metal layers (1/3 of atoms removed from ordered positions) sandwich planar boron honeycomb layers. One of the two W-sites shows a random defect of about 73%. Strong metal boron and boron-boron bonds are responsible for high mechanical stability. Although W

1-x B

3 at about 80 at.% B is the metal boride richest in boron, it contains no directly linked three-dimensional boron framework. The solubility of Rh, Ir, Ni, Pd and Pt in W

1-x B

3 as well as of Rh in Mo

1-x B

3 has been investigated in as cast state and after annealing. Furthermore, phase equilibria in the boron rich part of the corresponding isothermal sections W-TM-B (TM = Rh, Ir at 1100 °C, TM = Ni, Pd at 900 °C and TM = Pt at 800 °C) and Mo-Rh-B (at 1100 °C) have been established. A ternary compound only forms in the system W-Ir-B: τ

1-W

1-x Ir

x B

2 with ReB

2 structure type (space group P6

3/mmc; a = 0.2900, c = 0.7475 nm). The type of formation and crystal structure of diborides W

1-x TM

x B

2 (TM = Ru, Os, Ir) isotypic with ReB

2 were studied by x-ray powder diffraction and electron probe microanalysis in as cast state and after annealing at 1500 °C. Accordingly, W

0.5Os

0.5B

2 (a = 0.29127(1), c = 0.7562(1) nm) forms directly from the melt, whereas W

0.4Ru

0.6B

2 (a = 0.29027(1), c = 0.74673(2) nm) and W

0.6Ir

0.4B

2 (a = 0.29263(1), c = 0.75404(8) nm) are incongruently melting. Annealing at 1500 °C leads in case of the iridium compound to an almost single-phase product but the same procedure does not increase the amount of the ruthenium diboride.

Organisation(s)
Department of Physical Chemistry, Department of Mineralogy and Crystallography
External organisation(s)
Technische Universität Wien
Journal
Journal of Phase Equilibria and Diffusion
Volume
35
Pages
384-395
No. of pages
12
ISSN
1547-7037
DOI
https://doi.org/10.1007/s11669-014-0291-0
Publication date
08-2014
Peer reviewed
Yes
Austrian Fields of Science 2012
104017 Physical chemistry, 105113 Crystallography
Keywords
ASJC Scopus subject areas
Condensed Matter Physics, Metals and Alloys, Materials Chemistry
Portal url
https://ucrisportal.univie.ac.at/en/publications/c5be14e7-89f6-4430-9026-3e3b666ad32a