The high ionic conductivity in lithium lanthanum titanate perovskite ceramics, Li3x La(2/3)‑x TiO3 (LLTO), is well-known for the x ≈ 0.11 lithium concentration. The grain conductivity is approximately 10–3 S·cm–1 at room temperature, which makes this compound one of the best candidates for the development of solid-state electrolytes. However, lower grain boundary conductivity (10–6 to 10–4 S·cm–1) blocks lithium diffusion. In order to increase the total conductivity of LLTO ceramics, single crystal fibers of lanthanum aluminate (LAO) were inserted into its green ceramic matrix. Our hypothesis is that single crystal fibers are capable of inducting LLTO abnormal grain growth, thus improving the overall electrical conductivity of the composite. The results show that LAO single crystals act like seeds, creating abnormal grain growth at the LaAlO3 fiber surface. The impedance spectroscopy shows that the new composites have a substantial relative enhancement of total ionic conductivity (more than 200%) in comparison with the monolithic ceramic samples. This result shows the possibility of developing a novel composite design as a candidate for solid electrolyte applications.

No abstract

ResumoNeste trabalho foram quantifi cados o tamanho de grão e a porosidade de uma amostra de zircônia estabilizada com ítria (ZEI) sinterizada a 1500 °C/ 2 h e a fração volumétrica das fases ZEI, NiO e poros de um compósito de ZEI/NiO sinterizado a 1500 °C/ 2 h. Utilizando o programa de análise de imagens ImageJ foi possível tratar as imagens removendo ruídos e evidenciando as regiões de interesse de análise. Após as imagens serem analisadas, foi feito o tratamento estatístico dos dados como sugerido nas normas ASTM E 562-02 e ASTM E 1382-97. As frações volumétricas obtidas desta maneira foram 50 ± 7% de NiO, 32 ± 2% ZEI e 17 ± 7% poros. O tamanho médio de grãos da ZEI foi 4,6 ± 0,2 μm e sua porosidade 1,5 ± 0,2%. Os resultados de porosidade foram comparados com os valores obtidos utilizando o método baseado no princípio de Arquimedes. A diferença entre os valores permitiu por este método quantifi car somente a porosidade aberta, enquanto a análise de imagens quantifi ca também os poros fechados. Palavras-chave: microscopia quantitativa, processamento de análises digitais, análise microestrutural. Abstract In this work grain size and porosity of Yttria Stabilized Zirconia (YSZ) sintered at 1500 °C/ 2 h and the volume fraction of the phases YSZ, NiO and pores in a YSZ

No abstract

In this work, cobalt and zinc-doped Ce 0.8 Gd 0.2 O 1.9 samples were prepared starting from a commercial nanopowder and compared to the undoped material. The powder samples were pressed and afterwards sintered by a two-step procedure, before characterization by X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Impedance Spectroscopy (IS) in air. Cobalt or zinc additions are effective as sintering aid, allowing peak sintering temperatures around 1000°C to reach densifications above of 93% of theoretical density, showing no evidence for the presence of secondary phases. The total conductivity at 800 °C of pressed Zn-doped samples (6.7x10 -2 S/cm) and Co-doped samples (7.5x10 -2 S/cm) is similar for undoped samples (7.2x10 -2 S/cm) showing that Zn and Co has a positive effect on densification without compromising the electrical conductivity.