Skip to Main content Skip to Navigation
Theses

Céramiques diélectriques commandables pour applications micro-ondes : composites à base de titanate de baryum-strontium et d'un oxyde non ferroélectrique

Abstract : Since the last decades, dielectric ceramics have been considered as attractive for microwave applications as tunable dielectric resonators or phase shifters. For that, ceramic devices should be tunable – change in dielectric constant with applied voltage- with moderate to low dielectric constant (30 to 1000) and loss tangent as low as possible. To reconcile these properties, composite ceramics based on Ba0.6Sr0.4TiO3 (BSTO) and a non-ferroelectric oxide with a low dielectric constant (MgTiO3 or MgO) were synthesised. The aim of this study was to correlate the microstructure with the dielectric properties, especially the Curie temperature and the dielectric relaxation phenomena.
Ceramics with nanometric sized grains were obtained by hot uniaxial pressing of attrition milled powders in order to be compared with micrometric sized grains ceramics obtained by conventional way. The density of the milling balls and the viscosity of the slurry control the size and the morphology of the milled powders. The hypothesis that nanometric ceramics should improve the performances of the microwave devices was inaccurate. Of course the reduction of the grain size allowed the reduction of permittivity but to the detriment of tunability and loss tangent. Micrometric ceramics doped with Mn have led to the best properties. However, the measured loss tangents seamed to reach a lower limiting value when the materials were optimised; it may be attributed to intrinsic losses due to a dipolar relaxation phenomenon in the range of the GHz. Experiments in the infrared range should be performed.
A drastic decrease of the Curie temperature (Tc) is observed when the amount of MgTiO3 or MgO increases in the composites. It shows a reaction between BSTO and the non-ferroelectric oxide, only observed by XRD for MgTiO3. Thus, a slight interdiffusion can reduce significantly Tc and in consequence the permitivity and the tunability. A doping refinement of ceramics should improve the performances.
Complete list of metadatas

Cited literature [100 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-00357879
Contributor : Sandrine Tusseau-Nenez <>
Submitted on : Friday, February 13, 2009 - 9:20:44 AM
Last modification on : Friday, June 8, 2018 - 2:50:07 PM
Long-term archiving on: : Tuesday, June 8, 2010 - 9:48:16 PM

Identifiers

  • HAL Id : tel-00357879, version 1

Collections

Citation

Sandrine Nenez. Céramiques diélectriques commandables pour applications micro-ondes : composites à base de titanate de baryum-strontium et d'un oxyde non ferroélectrique. Matériaux. Université de Bourgogne, 2001. Français. ⟨tel-00357879⟩

Share

Metrics

Record views

1049

Files downloads

13040