Skip to Main content Skip to Navigation
Theses

Etude de couches minces à base de delafossite CuCr1-xFexO2(0 ≤ x ≤ 1) dopées au Mg déposées par pulvérisation cathodique radiofréquence en vue d'optimiser leurs propriétés thermoélectriques

Abstract : The aim of this thesis was to study the thermoelectric properties of delafossite type oxides thin-films deposited by RF-magnetron sputtering. Several thicknesses of CuCrO2:3%Mg, CuFeO2:3%Mg and CuCr0,84Fe0,16O2:3%Mg oxides were deposited on fused silica then annealed under vacuum at different temperatures in order to obtain delafossite structure. The optimal annealing temperature which leads to an acceptable thermoelectric properties is 550°C for CuCrO2:Mg and CuCr0,84Fe0,16O2:Mg thin films and 700°C for CuFeO2:Mg thin film. The optimal thickness is 100 nm for the delafossite with chrome and 300 nm for delafossite with iron. The electrical conductivity of the studied thin films increases with the temperature, while maintaining a positive and constant Seebeck coefficient for the three given compositions that implies a hopping mechanism. The power factor of CuCrO2:Mg, CuFeO2:Mg and CuCr0,84Fe0,16O2:Mg thin films for which the annealing temperature and the thickness were optimized, reached 59 µW.m-1K-2, 84 µW.m-1K-2 and 36 µW.m-1K-2 respectively at 200°C. The microstructural and structural analysis allowed to understand the variation of the power factor with the annealing temperatures and the thicknesses. In particular, they showed that the decrease in the electrical conductivity of the thin films annealed at high temperature is due to concomitant phenomena of film cracking and magnesium segregation. A thermal analysis using modeling with the finite element method has demonstrated that in the case of thin films, the thermal conductivity of the substrate can be substituted for the thermal conductivity of the film in the calculation of figure of merit. The validity of the modified figure of merit ((ZT)* = S2σ/ksubstrate) was given as a function of the film thickness, emissivity and thermal conductivity. The thermal conductivity of CuFeO2:Mg was measured using the 3ω method and it was 4.82 W.m-1k-1 at 25°C which is within the range of validity established for the use of (ZT)*[...]
Complete list of metadatas

Cited literature [287 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-02366197
Contributor : Abes Star :  Contact
Submitted on : Friday, November 15, 2019 - 5:17:24 PM
Last modification on : Friday, February 14, 2020 - 3:55:18 AM
Long-term archiving on: : Sunday, February 16, 2020 - 6:31:28 PM

File

2018TOU30270a.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-02366197, version 1

Collections

Citation

Inthuga Sinnarasa Barthelemy. Etude de couches minces à base de delafossite CuCr1-xFexO2(0 ≤ x ≤ 1) dopées au Mg déposées par pulvérisation cathodique radiofréquence en vue d'optimiser leurs propriétés thermoélectriques. Matériaux et structures en mécanique [physics.class-ph]. Université Paul Sabatier - Toulouse III, 2018. Français. ⟨NNT : 2018TOU30270⟩. ⟨tel-02366197⟩

Share

Metrics

Record views

68

Files downloads

307