In-Operando Diffraction and Spectroscopic Evaluation of Pure, Zr-, and Ce-Doped Vanadium Dioxide Thermochromic Films Derived via Glycolate Synthesis.

Stanislav Kurajica,Mattia Gaboardi,Ivana Katarina Munda,Ana Lozančić,Lara Gigli,Jasper Rikkert Plaisier,Ivana Panžić,Vilko Mandić,Sanja Lučić Blagojević,Juraj Šipušić,Lucija Višić,Katarina Mužina

doi:10.3390/nano10122537

Abstract

Pure and doped vanadia (VO2, V0.98Zr0.02O2, V0.98Ce0.02O2) samples were prepared by wet chemistry synthesis from vanadyl glycolate intermediate phase and tape casted into films. Combining in-operando grazing incidence synchrotron X-ray diffraction and Raman spectroscopy, we studied the structural evolution of the films under isothermal conditions. The setup allowed assessment of the thermochromic functionality with continuous monitoring of the monoclinic to tetragonal transition in pure and doped vanadia phases, responsible for the transmission and reflection of light in the infrared part of the solar spectrum. The materials characterisation by X-ray diffraction beamline (MCX) goniometer demonstrated ideal performance, combining flexible geometry, high resolution, and the potential to accommodate the multi-channel equipment for in-operando characterisation. This method proved viable for evaluating the relevant structural and physical, and thereof functional properties of these systems. We revealed that dopants reduce the transition temperature by 5 °C on average. The synthetic route of the films was held responsible for the observed phase separation. The more favourable behaviour of cerium-doped sample was attributed to cerium alkoxide behaviour. In addition, structural, microstructural, thermal, and spectroscopic characterisation on powder samples was performed to gain more insight into the development of the phases that are responsible for thermochromic features in a broader range of doping ratios. The influence of the dopants on the extent of the thermochromic transition (transmission to reflection hysteresis) was also evaluated using (micro) structural, thermal and spectroscopic methods of powder samples. Characterisations showed that zirconium doping in 2, 4, and 6 mol% significantly influenced the phase composition and morphology of the precursor. Vanadium oxides other than VO2 can easily crystallise; however, a thermal treatment regime that allowed crystallisation of VO2 as a single phase was established.

Highlights

Vanadium dioxide (VO2) is a thermochromic material that undergoes a reversible phase transition at 68 ◦C from a low-temperature monoclinic and semiconductor phase, that is permeable to infrared radiation, into a high-temperature tetragonal-rutile metallic phase, that is semi-permeable to infrared radiation [1]
In this article, we report on the synthesis of the same compositions in form of powders, followed by a thorough characterisation by means of powder X-ray diffraction (XRPD), thermal analyses (DTA/thermogravimetric analysis (TGA)/DTGA/Differential scanning calorimetry (DSC)), Scanning Electron Microscopy (SEM), and vibration spectroscopy (FTIR)
In-operando Grazing Incident synchrotron X-ray Diffraction (GIXRD) was successfully used for revealing the specificities of the investigated vanadia thermochromic system

Summary

Introduction

Vanadium dioxide (VO2) is a thermochromic material that undergoes a reversible phase transition at 68 ◦C from a low-temperature monoclinic and semiconductor phase, that is permeable to infrared radiation, into a high-temperature tetragonal-rutile metallic phase, that is semi-permeable to infrared radiation [1]. Thanks to this transformation, VO2 can be used as a key element of smart windows by depositing thermochromic films onto the glass. The strategy to modify VO2 by doping with different metals such as W, Mo, Ti, Zr, etc., may be feasible for reducing Tc while increasing Tlum and ∆Tsol and improving the visual appearance [4,5]

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Results

Conclusion