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Identifier 000423144
Title Μελέτη θερμοχρωμικών υλικών χαμηλής θερμοκρασίας ανάπτυξης, με βάση το διοξείδιο του Βαναδίου (VO2)
Alternative Title Study of Vanadium dioxide (VO2)-based thermochromic materials grown at low temperature
Author Γκαγκαουδάκης, Εμμανουήλ
Thesis advisor Κυριακίδης, Γεώργιος
Reviewer Χατζόπουλος, Ζαχαρίας
Ηλιόπουλος, Ελευθέριος
Ράπτης, Ιωάννης
Πελεκάνος, Νίκος
Κωνσταντινίδης, Γεώργιος
Στρατάκης, Εμμανουήλ
Abstract The subject of the present PhD thesis was the study of VO2-based thermochromic materials grown at low deposition temperature. RF sputtering technique was used to deposit undoped and Mg-doped VO2 films at the low deposition temperature of 300 oC, on various substrates namely Float Glass, K-Glass (SnO2 pre-coated Float Glass), Flexible Glass, Fused Silica and Si. Moreover, hydrothermal synthesis was employed to grow VO2 in powder form. Subsequently, VO2 powder was converted into film through a specific procedure, described in the experimental section. The effect of film thickness and Oxygen content in the plasma during deposition on the thermochromic/optical properties of VO2 films were investigated for rf-sputtered films deposited on K-Glass substrates. In contrast to K-Glass substrates where the films were thermochromic independent the thickness, on Float Glass substrates only the thinner film showed thermochromism, while the rest of them were annealed in reducing atmosphere in order to be converted to thermochromic. In addition, thermochromic undoped VO2 films were successfully deposited on flexible glass for the first time, while by using the same deposition parameters thermochromic films were also deposited on Fused Silica glass substrates. In order to enhance the luminous transmittance of the thermochromic VO2 films two methods were employed, the deposition of a ZnO antireflective coating and the introduction of Mg dopant. In the former, the optimum ZnO thickness for a constant VO2 thickness was determined, while in the latter the maximum quantity of Mg content was identified, in order to maximize the luminous transmittance without destroy the thermochromic characteristics of the VO2 films. Hydrothermal synthesis was used as an alternative method to grow thermochromic VO2. It is an easy and cheap method to synthesize VO2 in the form of powder which subsequently can be turned in film at temperatures lower than 100 oC. The latter is the main advantage of this method, since it allows the growth of thermochromic VO2 films at near RT even on plastic substrates. In this work, the effect of hydrothermal synthesis parameters such as the concentration of Vanadium precursor (V2O5), the molar ratio of Vanadium source to reducing agent (Oxalic acid), the pH of the initial solution of V2O5-Oxalic acid as far as the role of Thiourea as an additive on the thermochromic properties of VO2 powder, were investigated. Moreover, the thermochromic VO2 powder was mixed with an appropriate agent forming a transparent film which successfully deposited on both glass and plastic substrate keeping its thermochromic characteristics. In an alternative method, the growth of thermochromic VO2 film was taken place during the hydrothermal synthesis on a KGlass substrate. The thermochromic properties of this film were comparable to those of the rf-sputtered film on the same substrate. Finally, in order to test the practical functionality of the thermochromic coatings, two doll-houses were constructed. One of them had K-Glass glazing as window, while the other had K-Glass with rf-sputtered thermochromic VO2 coating as a window. By heating them externally and measuring the internal temperature, a decrease of about 5 oC was found for the doll-house with the thermochromic windows i.e. clearly demonstrating the comparable advantages of using thermodynamic windows in buildings.
Language Greek
Subject Hydrothermal synthesis
Low deposition temperature
RF-Sputterring
Θερμοχρωμικά υλικά
Λεπτά υμένια
Υδροθερμική σύνθεση
Issue date 2019-09-09
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Physics--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/6/c/f/metadata-dlib-1560434760-120831-2694.tkl Bookmark and Share
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