Electrochromic Vanadium Oxide Thin Films: From a Layered to a Tunnel Structure

Stojkovikj, Sasho and Koleva, Violeta and Najdoski, Metodija (2014) Electrochromic Vanadium Oxide Thin Films: From a Layered to a Tunnel Structure. In: XXIIIrd Congress of Chemists and Technologists of Macedonia, 8-11 Oct 2014, Ohrid, Macedonia.

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Abstract

Vanadium oxide-based materials are very promising electrochromic materials since they have the potential to broaden the color palette displayed by inorganic electrochromics, and thus to extend the range of their functions.
The one-stage chemical deposition on FTO(define) substrates from a bath containing NaVO3 and (C2H5)2SO4 at 85 °C yields xerogel thin films with the composition Na0.33V2O5·H2O. The as-deposited films adopt a layered structure: double V2O5 slabs stacked along the c-axis of a monoclinic unit cell which are separated by Na+ ions and water molecules. The complete dehydration at 375 oC results in the transformation of the layered structure into a tunnel structure of monoclinic NaV6O15 (or Na0.33V2O5). This structure is built up from V6O15 layers which are linked to each other by one oxygen atom per a unit cell giving rise to unidirectional tunnels. The Na+ ions are localized within the tunnels where they can be easily intercalated. Three kinds of thin films with different thickness are studied: two films having a layered structure with compositions Na0.33V2O5·H2O (as-deposited) and Na0.33V2O5·0.3H2O (annealed at 250 °C) and thin films having a tunnel structure (annealed at 400 °C). The structure and surface morphology are examined by XRD, IR spectroscopy, SEM and AFM techniques. The electrochemical (cyclic voltammetry measurements) and optical properties (UV- Vis spectroscopy) are studied in LiClO4 in propylene carbonate as an electrolyte. The cyclic voltammograms are characterized by three pairs of oxidation/reduction peaks related to the redox processes at different vanadium V(V) and V(IV) sites accompanied with the reversible lithium intercalation/deintercalation. All thin films exhibit two-step electrochromism from yellow to green, and then to blue with high values of the transmittance variance up to 68 % at 900 nm wavelength. This is a promising result for a potential application of the vanadium(V) oxide thin films in electrochromic devices.

Keywords: electrochromism, vanadium oxides, layered and tunnel structure

Item Type:	Conference or Workshop Item (Poster)
Subjects:	Natural sciences > Chemical sciences Engineering and Technology > Materials engineering Natural sciences > Other natural sciences
Divisions:	Faculty of Technology
Depositing User:	Saso Stojkovik
Date Deposited:	04 Mar 2024 13:24
Last Modified:	04 Mar 2024 13:24
URI:	https://eprints.ugd.edu.mk/id/eprint/33813

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