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

• Published in: arXiv.org 2018-04
• Main Authors: Zupanič, E, H J P van Midden, M van Midden, Šturm, S, Tchernychova, E, V Ya Pokrovskii, Zybtsev, S G, Nasretdinova, V F, Zaitsev-Zotov, S V, Chen, W T, Pai, W W, Bennett, J C, Prodan, A
• Format: Article
• Language: English
• Subjects: Charge density waves; Columns (structural); Diffraction; Diffraction patterns; Electron diffraction; Synchrotron radiation; Unit cell; X-ray diffraction
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1804.02232

The basic and the charge density wave (CDW) structures of the monoclinic \(NbS_3-II\) 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 \(P2_1/m\) 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, \(\beta_0\) = 110.695(4) deg), with all Nb and S atoms in \(2e\) special positions. The two CDWs, with \(\vec{q_1}\) = (0, 0.298,0) and \(\vec{q_2}\) = (0, 0.352, 0), form their own modulation unit cells (\(a_m\) = \(2a_0\), \(b_m\) = \(b_0/q_{jb}\), \(c_m\) = \(c_0\), \(\beta_m\) = \(\beta_0\)) and are ordered pairwise along adjacent isosceles TP columns. The symmetries of both \(\vec{q_j}\) modes belong to the space group \(Cm\) and are related according to the \(2a\) special positions. If considered as long-period commensurate, the entire modulated structure with both CDWs included is best described with an enlarged unit cell (\(a\) = \(2a_0\), \(b\) = \(37b_0\), \(c\) = \(c_0\), \(\beta\) = \(\beta_0\)), with all Nb and S atoms in \(1a\) positions of the space group \(P1\).