Application of atomic pair distribution function analysis to materials with intrinsic disorder. Three-dimensional structure of exfoliated-restacked WS₂: Not just a random turbostratic assembly of layers

The three-dimensional structure of metastable exfoliated-restacked WS₂ (r-WS₂) has been determined by the atomic pair distribution function (PDF) technique. We show that the structure of r-WS₂ is not a random turbostratic assembly of layers, as previously thought, but it can be better regarded as a monoclinic structure with considerable intrinsic disorder. At room temperature, the atomic-scale structure of r-WS₂ is well described in the space group P112₁ of the monoclinic system with four formula units in the cell, and lattice parameters a = 3.270(5) A, b = 5.717(5) A, c = 12.309(5) A, and γ = 88.43°. Analysis of the X-ray scattering data, collected with Synchrotron radiation (λ = 0.202°) over a wide scattering angle, shows that the metastable material is built of layers of distorted (WS₆) octahedral units, in contrast to hexagonal 2H-WS₂ which is built of layers of perfect (WS₆) trigonal prisms. A characteristic structural feature of the restacked material is that W atoms within a single layer form zigzag chains along the a axis of the unit cell via short metal-metal bonds of length 2.77(1) and 2.85(1) A, in agreement with previous two-dimensional electron diffraction studies.