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 P112(1) of the monoclinic system with four formula units in the cell, and lattice parameters a = 3.270(5) Angstrom, b = 5.717(5) Angstrom, 12.309(5) Angstrom, and gamma = 88.43 degrees. Analysis of the X-ray scattering data, collected with Synchrotron radiation (lambda = 0.202 A) 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) Angstrom, in agreement with previous two-dimensional electron diffraction studies.