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

Autor(en)
I. Zeiringer, P. Rogl, A. Grytsiv, Julia Polt, E. Bauer, G. Giester
Abstrakt

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(en)
Institut für Physikalische Chemie, Institut für Mineralogie und Kristallographie
Externe Organisation(en)
Technische Universität Wien
Journal
Journal of Phase Equilibria and Diffusion
Band
35
Seiten
384-395
Anzahl der Seiten
12
ISSN
1547-7037
DOI
https://doi.org/10.1007/s11669-014-0291-0
Publikationsdatum
08-2014
Peer-reviewed
Ja
ÖFOS 2012
104017 Physikalische Chemie, 105113 Kristallographie
Schlagwörter
ASJC Scopus Sachgebiete
Condensed Matter Physics, Metals and Alloys, Materials Chemistry
Link zum Portal
https://ucrisportal.univie.ac.at/de/publications/c5be14e7-89f6-4430-9026-3e3b666ad32a