D8 discover twin twin

To assess the purity of the Na_3.2Ni_0.2V_1.8(PO₄)₂F₂O sample, X‐ray Diffraction (XRD) measurements were performed. The data was collected at room temperature over the 2θ angular range of 10° ≤ 2θ  ≤ 110° with a step size of 0.01° using a Bruker D8 ADVANCE diffractometer operating with Cu‐Kα radiation. The full pattern‐matching refinements were performed using the Jana2006 program package.^[29] The backgrounds were estimated by a Legendre function, and the peak shapes were described by a pseudo‐Voigt function. The Rietveld refinements were then performed using high‐resolution synchrotron XRD data collected from the 11 BM beamline of the Advanced Photon Source (λ = 0.1173 Å).
A specific cell with a beryllium window was used for recording operando X‐ray diffraction data in reflection mode to study the reaction mechanism of Na_3.2Ni_0.2V_1.8(PO₄)₂F₂O active cathode material during electrochemical cycling. The XRD patterns were recorded every hour. Diffractograms were registered during the electrochemical charge/discharge process, using Bruker D8 Discover Twin‐Twin with an advanced diffractometer in Bragg–Brentano geometry with Cu‐Kα radiation (λ  =  1.540, 60 Å, 15° ≤ 2θ ≤ 40°) and a Bio‐Logic VMP3 potentiostat at a rate of C/20.

The phase formation was identified by the X-ray powder diffraction technique using Bruker D8 Discover Twin-Twin with an advance diffractometer in Bragg–Brentano geometry with Cu Kα radiation (λ = 1.5406 Å, 10° ≤ 2θ ≤ 90°). Refinements were carried out using the FullProf program based on the Rietveld method.^{18 (link)} To investigate the morphology of the prepared samples, the scanning electron microscope (XL30 FEG ESEM, FEI) was used with an accelerating voltage of 15 kV under high vacuum. Dielectric impedance measurements were determined using the double platinum electrode configuration of Solartron SI-1260 in the frequency range of 0.1–10⁶ Hz and the 383–613 K temperature range.