Bridging fromThCr2Si2-type materials to hexagonal dichalcogenides: Anab initioand experimental study of

Oliver Tiedje

¹

,

E. E. Krasovskii

²

,

W. Schattke

³

et al.

Abstract

A different class of layered systems derived from ThCr 2 Si 2 -type materials is introduced and studied. We present preparation, x-ray analysis, band-structure, and total-energy calculations of KCu 2 Se 2 , a semimetallic representative of this class. The crystal has an orthorhombic symmetry by a slight distortion of a tetragonal lattice. From calculation, interesting quasi-two-dimensional electronic properties are obtained similar to those of the well-known hexagonal transition-metal dichalcogenides. A complex picture of chemical bonding in this mixed-valency compound is elucidated by electronic structure calculations. The changes in the band structure caused by the symmetry reduction and their implications for the total energy are discussed. The ab initio band-structure calculation is performed with the extended linear augmented plane-wave k•p method, with all the states down to K 3s being treated as valence states. The total energy is computed using the augmented Fourier component representation of the crystal potential.

Coloring, Distortions, and Puckering in Selected Intermetallic Structures from the Perspective of Group‐Subgroup Relations

“…The space group symmetry is reduced trough a translationengleiche symmetry reduction of index 2 from I 4/ mmm to Fmmm . This orthorhombic superstructure had previously already been observed for KCu 2 Se 2 97 and SrRh 2 As 2 98. The motif of layers of condensed tetrahedra is a basic one in the crystal chemistry of iron pnictide superconductors 96.…”

Nanosheets‐Assembled CuSe Crystal Pillar as a Stable and High‐Power Anode for Sodium‐Ion and Potassium‐Ion Batteries

“…With the increase in the inserted K + content, several new phases appear accompanied by the disappearance of CuSe phase. [36] Furthermore, an additional reflection is observed at 32.0° at low working potential and disappears upon charging. However, the signals located at 27.4°, 35.6°, and 36.9° can be indexed based on Adv.…”

An experimental study on the preparation of tochilinite-originated intercalation compounds comprised of Fe1−xS host layers and various kinds of guest layers

“…Mö ssbauer spectroscopy studies on both natural and synthetic tochilinites indicate that the Fe atoms in the Fe 1Àx S layers of tochilinite are at the +2 valence state (Rusakov et al, 1998;Kozerenko et al, 2001;Chistyakova et al, 2005Chistyakova et al, , 2006. Thus, the Fe-vacancies in the Fe 1Àx S layers of tochilinite would probably result in an electron-deficiency state, i.e., the valence electrons in a single Fe 1Àx S layer is not enough to fill its valence bands, similar to the electron-deficient ThCr 2 Si 2 -type chalcogenides (Berger andVan Bruggen, 1984, 1985;Berger, 1989;Karlsson et al, 1990;Zhang et al, 1996;Tiedje et al, 2003;Ronneteg et al, 2004;Yablonskikh et al, 2006). Therefore, holes will be produced in the valence bands, which indicate that the Fe 1Àx S layer of tochilinite may be a hole-conductor.…”

“…The typical electronic property of the ThCr 2 Si 2 -type chalcogenide layers (e.g., M 2 X 2 layers with M = Cu, Co, Fe, and T = S, Se) is that they can be both metallic hole-conductors (i.e., p-type conductors) and semiconductors depending on the presence or absence of holes in the valence bands (Berger andVan Bruggen, 1984, 1985;Berger, 1989;Karlsson et al, 1990;Ouammou et al, 1995;Zhang et al, 1996;Tiedje et al, 2003;Ronneteg et al, 2004;Yablonskikh et al, 2006). The upper valence bands of the ThCr 2 Si 2 -type chalcogenide layers are mainly made up of the p states of the chalcogen atoms.…”