VOPO₄·H₂O: A Stacking Faults Structure Studied by X-ray Powder Diffraction and DFT-D Calculations

Abstract

The dehydration process of VOPO(4)·2H(2)O occurs in two steps corresponding to successive elimination of the two crystallographically distinct water molecules. The intermediate phase VOPO(4)·H(2)O has been stabilized for X-ray powder diffraction studies. The resulting data suggest a tetragonal cell (a = 6.2203(2) Å and c = 6.18867(7) Å), but an important anisotropy in the line broadening points out the necessity of considering a not perfectly organized structure. Because of the layered structure of this compound, density functional theory calculations including dispersion corrections have been carried out to evaluate the possible presence of stacking faults. The results of these calculations give information about the nature of the translations and their probabilities using a Boltzmann distribution. DIFFaX+ simulations of the X-ray powder diffraction pattern have been carried out using the results of the theoretical calculations and confirm the presence and nature of stacking faults.

Analysis and Prediction of Stacking Sequences in Intercalated Lamellar Vanadium Phosphates

“…Such shifts of layers are in agreement with previously reported layer stacking in nonintercalated VOPO 4 ·H 2 O. [6] The absence of a relative shift for the VPO layers would lead to steric effects between the oxygen atoms and the water molecules of adjacent layers (distance is Ͻ2.5 Å). Similarly, the relative shift [0.5; 0.5] would lead to very strong steric effects between the water molecules of adjacent VPO layers (distance is Ͻ0.5 Å).…”

“…The approach used to plot energy vs. relative shift of adjacent VPO layers is a three-step method: (i) the geometry of an isolated layer is optimized, (ii) the isolated layer is used to model structures with different relative shifts and fixed interlayer distances and (iii) energy vs. layer/layer shift is plotted from the results of DFT calculations. [5][6][7] Synthesis: Cd(VOPO 4 Structure Determination: The crystal structure of Cd(VOPO 4 ) 2 · 4H 2 O was determined using a four-circle Nonius KappaCCD diffractometer with graphite monochromated Mo-K α radiation (λ = 0.71073 Å) ( Table 2). The intensities were collected with the program COLLECT for the Kappa CCD in the ω-φ scanning mode.…”

Intercalation chemistry of layered vanadyl phosphate: a review

“…In accordance with the previous results reported for VOPO 4 Á2H 2 O [12,57], it can be assumed that the water evolved initially is that inserted into holes of the lattice, the remaining water being that directly coordinated to the vanadyl groups. The structure of vanadyl phosphate monohydrate (tetragonal cell, a = 6.2203(2) Å , c = 6.18867(7) Å ) was determined from X-ray powder diffraction and the presence of stacking faults was confirmed using DFT-D calculations [58]. The thermomechanical measurements, TGA and thermoelectric power measurements confirmed two-step mechanism of dehydration.…”

How Water Accelerates Bivalent Ion Diffusion at the Electrolyte/Electrode Interface

“…Layered VOPO 4 has been used as host for monovalent‐ions, but, to the best of our knowledge, was never reported for MV cations. VOPO 4 has a typical (001) peak at around 21.5°, corresponding to a d value of 4.2 Å, while the intercalation of H 2 O molecules into the interlayer significantly expanded basal spacing to 7.4 Å, thus pushing the peak to approximately 11.9° for hydrated VOPO 4 ⋅2 H 2 O . The thermogravimetric analysis (Figure S1) proved that the hydration–dehydration of VOPO 4 is reversible, because after being heated to 500 °C, the peak of VOPO 4 ⋅2 H 2 O shifted back.…”