The crystal structure and magnetic and electrical properties of β-US2

Abstract

The crystal structure of β‐US2 was refined using single crystal X‐ray diffraction data. The lattice constants at room temperature are: a = 8.4803 Å, b = 7.1139 Å, and c = 4.1205 Å. The uranium atom is coordinated by nine sulphur atoms: two at a distance of 2.713 Å, two at 2.896 Å, two at 3.141 Å, one at 2.747 Å, one at 2.826 Å, and one at 2.888 Å. The magnetic measurements were carried out in the temperature range 4.2 to 1000 °K. The increase of the effective magnetic moment from 3.08 to 3.28 BM with temperature is explained on the assumption that the ground state is composed of four closely spaced singlets. The semiconducting character in the temperature range 4.2 to 650 °K was established with a forbidden gap ΔE≈1.2 eV.

Analysis of Magnetization Behavior in Magnetic Semiconductor β-US2

“…β-US 2 crystallizes in the orthorhombic TiNiSi-type crystal structure [1,2]. Sulfur atoms occupy two inequivalent crystallographic sites both having the same monoclinic local Wyckoff symbol 4c.…”

“…One of the 4c sites can be replaced by other chalcogen atoms to form USeS and UTeS [2]. All those compounds show a semiconducting or semimetallic electrical conductivity with small number of carriers [1,2]. Among the three compounds, β-US 2 has the largest resistivity.…”

“…Among the three compounds, β-US 2 has the largest resistivity. The resistivity increases steeply below about 100 K showing insulating behavior at low temperature [1,3], suggesting that uranium may be in the tetravalent state, U 4+ (S 2− ) 2 .…”

Non-magnetic to Magnetic Transition under High Pressure in Narrow-Gap Semiconductor β-US2

“…Uranium chalcogenide compound β-US 2 is a narrow-gap semiconductor with the energy band gap of 90 K. 1) We have studied the physical property of the orthorhombic β-US 2 using single crystals made by a chemical transport method.…”

Electron Transport Properties of UAsSe

“…The in-plane resistivity for the UAs2 [7] shows typical magnetic metal behaviour. On the other hand, the resistivity along c-axis for the US2 [8] (presumably similar to USe2) shows activation behaviour at low temperatures. Intermediate character of the resistivity curves for UAsSe may show its intermediate electronic state.…”