Abstract
The crystal structure of CrAs was investigated using synchrotron X-ray single-crystal diffraction for separate dependences on temperature (30–400 K) and on pressure (0–9.46 GPa). The isosymmetrical magnetostructural phase transition at T N = 267 K can induce a change in the microstructure by twinning due to a crossing of the orthohexagonal setting of the unit-cell parameter ratio c/b. Within the crystal structure, one particular Cr–Cr distance exhibits anomalous behavior in that it is nearly unaffected by temperature and pressure in the paramagnetic phase, which is stable above 267 K and at high pressures. The distinction of this shortest Cr–Cr distance might be of importance for the superconducting properties of CrAs.
Highlights
IntroductionChromium arsenide (CrAs) crystallizes in the orthorhombic
Chromium arsenide (CrAs) crystallizes in the orthorhombicMnP-type structure (Pnma, Z = 4), commonly described as a distorted variant of the NiAs-type structure (P63/mmc, Z = 2)(Fig. 1) (Rundqvist, 1962)
The measured Cr–Cr distances are in very good agreement with the data reported by Shen et al (2016) (Fig. S4) and in good agreement with those reported by Selte et al (1971)
Summary
Chromium arsenide (CrAs) crystallizes in the orthorhombic. MnP-type structure (Pnma, Z = 4), commonly described as a distorted variant of the NiAs-type structure (P63/mmc, Z = 2). (Fig. 1) (Rundqvist, 1962). The ideal NiAs-type structure can be understood as a hexagonal close-packed As sublattice interpenetrated by a primitive hexagonal Cr sublattice (Tremel et al, 1986). The Cr atoms are sixfold coordinated by the As atoms in the shape of an octahedron [CrAs6]. The As atoms are sixfold coordinated by the Cr atoms in the shape of a trigonal prism [AsCr6]. In the MnP structure, both the [CrAs6] octahedra and the [AsCr6] prisms are distorted. The [CrAs6] octahedra form face-connected columns along the aaxis, which in turn are connected by shared edges.
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