Structure of the two-dimensional incommensurate charge-density wave in (PO2)4(WO3)8 at 20 K

Jens Lüdecke, Andreas Jobst, Sandra Geupel, and Sander van Smaalen
Phys. Rev. B 64, 104105 – Published 23 August 2001
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Abstract

The incommensurate charge-density waves (CDW’s) in the m=4 phosphate bronze (PO2)4(WO3)2m have been studied by synchrotron-radiation x-ray scattering. The CDW is found to correspond to a 2q state for all temperatures below the first phase transition at Tc1=80K. The second phase transition at Tc2=52K is found to involve the development of mixed second-order satellites within the primary CDW. The incommensurately modulated structure has been determined at T=20K. The structure remains orthorhombic down to T=20K. At 20 K the lattice parameters are a=5.294(1)Å, b=6.591(2)Å, and c=17.415(16)Å. The two-dimensional CDW is characterized by the modulation wave vectors q1=[0.330(2),0.292(2),0.000(2)] and q2=(0.330,0.292,0). The (3+2)D superspace group was found as P212121(α,β,0)(α,β,0). The primary CDW comprises the satellite reflections (hklm1m2) with (m1m2) equal to (±1,0) and (0,±1). Below Tc2 additional satellite reflections develop, that correspond to (m1m2)=±(1,1). Accordingly, harmonic modulation amplitudes (1,0), (0,1), and (1,1) were incorporated into the structure model. Refinement against 4970 observed reflection intensities resulted in a fit with R=0.039. The periodic lattice distortion shows that the CDW is located at the centers of the WO3 slabs. The CDW is interpreted in terms of the formation of clusters of six tungsten atoms, that are linked together to form larger clusters of 12 to 18 atoms.

  • Received 14 September 2000

DOI:https://doi.org/10.1103/PhysRevB.64.104105

©2001 American Physical Society

Authors & Affiliations

Jens Lüdecke, Andreas Jobst, Sandra Geupel, and Sander van Smaalen*

  • Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany

  • *Email address: smash@uni-bayreuth.de

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Issue

Vol. 64, Iss. 10 — 1 September 2001

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