The Basic and the Charge Density Wave Modulated Structures of NbS3-II

E. Zupanič; H. J. P. van Midden; M. van Midden; S. Šturm; E. Tchernychova; V. Ya. Pokrovskii; S. G. Zybtsev; V. F. Nasretdinova; S. V. Zaitsev-Zotov; W. T. Chen; W. W. Pai; J. C. Bennett; A. Prodan

doi:10.1103/PhysRevB.98.174113

paper

The Basic and the Charge Density Wave Modulated Structures of NbS3-II

arXiv:1804.02232 · doi:10.1103/PhysRevB.98.174113

Abstract

The basic and the charge density wave (CDW) structures of the monoclinic $N b S_{3} - I I$ polymorph were studied by synchrotron x-ray diffraction, ab-initio calculation, simulation of electron diffraction patterns and by atomic-resolution transmission electron and low-temperature scanning tunneling microscopies. It is shown that the basic structure belongs to the space group $P 2_{1} / m$ and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns ( $a_{0}$ = 0.96509(8) nm, $b_{0}$ = 0.33459(2) nm, $c_{0}$ = 1.9850(1) nm, $β_{0}$ = 110.695(4) deg), with all Nb and S atoms in $2 e$ special positions. The two CDWs, with $q_{1}$ = (0, 0.298,0) and $q_{2}$ = (0, 0.352, 0), form their own modulation unit cells ( $a_{m}$ = $2 a_{0}$ , $b_{m}$ = $b_{0} / q_{j b}$ , $c_{m}$ = $c_{0}$ , $β_{m}$ = $β_{0}$ ) and are ordered pairwise along adjacent isosceles TP columns. The symmetries of both $q_{j}$ modes belong to the space group $C m$ and are related according to the $2 a$ special positions. If considered as long-period commensurate, the entire modulated structure with both CDWs included is best described with an enlarged unit cell ( $a$ = $2 a_{0}$ , $b$ = $37 b_{0}$ , $c$ = $c_{0}$ , $β$ = $β_{0}$ ), with all Nb and S atoms in $1 a$ positions of the space group $P 1$ .

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