Microstructure effects on the thermoelectric response of doped SrTiO3

• Autor(a) principal: Resende, João Avelãs
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/12581
• topic: Engenharia de materiais; Termoelectricidade; Titanato de estrôncio; Cerâmica ferroeléctrica

Niobium doped SrTiO3 ceramics were prepared with varying density and grain size in order to study the effect on the thermoelectric properties and discover a possible way to enhance the figure of merit (ZT = S2 .σ.T.κ-1) of this oxide. The samples were prepared by the conventional solid-state reaction technique and the grain-size variation was carried-out by the variation of precursor powders, sintering and annealing time. Structural and microstructural characterization were carried-out by XRD, electron microscopy (SEM) and optical microscope (OM). The relative density was measured by Archimedes principle, with the theoretical densities calculated from the XRD spectra. The electrical resistivity and Seebeck coefficient were measured by ZEM-3. The thermal diffusivity was measured using a Laser Flash technique and the specific heat was measure by Differential Scanning Calorimetry (DSC), in order to obtain the thermal conductivity indirectly. The different doping compositions (5% and 20%) conjugated with the variations in density and grain size in the samples shows a potential way to improve ZT. While in the less doped samples, the higher ZT is related to the annealing time combined with larger grains and density; in the 20% Nb doped samples the smaller grain size and higher density, enhance the ZT values. The highest figure of merit obtained is 0.44 for 20% Nb doped composition, with a bimodal grain distribution. The value is the highest obtained for a Niobium doped SrTiO3 ceramic.