TALITA GISHITOMI FUJIMOTO

TALITA GISHITOMI FUJIMOTO

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Mechanical and electrical characterization of 8YSZ-ScCeSZ ceramics
2023 - FUJIMOTO, T.G.; SERIACOPI, V.; FERREIRA, L.A.S.; MACHADO, I.F.; MUCCILLO, E.N.S.
The effects of small amounts (up to 5 wt.%) of scandia- and ceria-stabilized zirconia on the electrical conductivity, and the elastic modulus and hardness of yttria-stabilized zirconia were investigated by impedance spectroscopy and nanoindentation tests, respectively. The main purpose of this work was to obtain solid electrolyte compounds with improved properties compared to those of the base materials. Solid electrolytes compounds were prepared by solid-state reaction synthesis with sintering at 1450 ºC for 4 h. All prepared compounds exhibit a cubic fluorite-type structure. The microstructure of the compounds consists of polygonal grains with low (< 2%) porosity. The mean grain size estimated by the intercept method was 5 ± 1 μm. The electrical conductivity of the compound ceramics is lower than that of the base material. Addition of scandia-stabilized zirconia is found to exert a beneficial effect on the matrix by increasing the elastic modulus, achieving 221 MPa for 5 wt.% of the additive.
Phase transformation/stabilization and ionic conductivity in tantalum oxide co‑doped zirconia‑scandia solid electrolyte
2022 - SOUZA, J.P.; FUJIMOTO, T.G.; BATISTA, R.M.; STEIL, M.C.; MUCCILLO, R.; MUCCILLO, E.N.S.
The influence of small amounts of tantalum oxide as co-dopant on phase transformation and stabilization, microstructure and ionic conductivity of zirconia-10 mol% scandia is reported in this work. Cylindrical pellets were prepared by solid state synthesis with sintering at 1500 °C for 5 h. High relative density values (> 95%) were achieved. Reduction of the enthalpy for the cubic ⇌β-rhombohedral phase transformation was found for increasing amounts of the co-dopant. Full stabilization of the cubic structure at room temperature was obtained with only 0.45 mol% tantalum oxide addition. The ionic conductivity of sintered specimens was investigated as a function of the temperature and oxygen partial pressure by impedance spectroscopy. The fully stabilized co-doped system revealed a pure ionic conduction behavior up to 800 °C with wide electrolytic domain. In the 700–800 °C range, the ionic conductivity of co-doped specimens is similar to that of pure zirconia-scandia.
Electrical conductivity of La0.9Sr0.1Ga0.8Mg0.2O3-y-La1.55Sr0.45Ga3O7+δ composite electrolyte
2021 - FUJIMOTO, T.G.; STEIL, M.C.; MUCCILLO, E.N.S.
Doped lanthanum gallate constitutes a family of solid electrolytes with high ionic conductivity, wide electrolytic domain, and good chemical stability. The combination of its properties turns some compounds of this family promising candidates for application in solid oxide cells operating at intermediate temperatures. In this work, La0.9Sr0.1Ga0.8Mg0.2O3-y - xLa1.55Sr0.45Ga3O7+δ with x = 0, 1, and 5 wt.% were investigated aiming to obtain a composite solid electrolyte with optimized properties compared to the parent material. Composite electrolytes were prepared by solid state reaction method and evaluated for densification, phase content, and microstructure. Electrical conductivity measurements were carried out as a function of temperature and oxygen partial pressure. Increase on densification and structural homogeneity were obtained with increasing fraction of the melilite phase. The electrical conductivity determined by impedance spectroscopy revealed a decrease of the bulk resistivity for increasing amounts of La1.55Sr0.45Ga3O7+δ.
Influence of yttria-stabilized zirconia on microstructure and electrical properties of doped lanthanum gallate
2019 - FUJIMOTO, TALITA G.; REIS, SHIRLEY L.; MUCCILLO, ELIANA N. dos S.
Lanthanum gallate with partial substitutions for strontium and magnesium shows higher ionic conductivity than traditional ionic conductors such as yttria-stabilized zirconia (8YSZ), and has been considered for application as solid electrolyte and electrode in Solid Oxide Fuel Cells operating at intermediate temperatures (500-700ºC). Parallel to the development of new solid electrolytes, improvement of the already known electrolytes has been one goal. In this work, the effects of adding 8YSZ to La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM), on the microstructure and electrical performance were investigated. Compound electrolytes consisting of up to 20 wt.% 8YSZ were prepared by solid state reactions. Sintered pellets with up to 10 wt.% 8YSZ achieved near full density after sintering at 1450ºC and reduction in the fraction of impurity phases. Addition of 8YSZ promoted grain growth to LSGM. The higher ionic conductivity was obtained for 1 wt.% 8YSZ addition with slight decrease of the apparent activation energy.
Effect of Pr on microstructure and dielectric properties of SrTiO3
2018 - FUJIMOTO, TALITA G.; MUCCILLO, ELIANA N. dos S.
Polycrystalline ceramics based on strontium titanate (SrTiO3) have attracted great attention in recent years due to their interesting dielectric properties, e.g. high electric permittivity and low dielectric loss. SrTiO3 has many applications in electronic devices, sensors, actuators, fuel cells, among others. Recently, the effects of dopants on the dielectric properties of SrTiO3 have been investigated. Lui et al. [1] were the first to report a giant electric permittivity in Sr0.09Pr0.01TiO3 (> 3,000) at room temperature. In this work, the effect of Pr (0.025, 0.05 and 0.075% mol Pr) on the microstructure and dielectric properties of SrTiO3 was studied in detail. Samples were characterized by density measurement, X-ray diffraction, scanning electron microscopy and impedance spectroscopy. The results show that sintered samples at 1500 ºC/6 h exhibit high densities (> 96% of the theoretical value), independent on the additive content. The average grain size of SrTiO3 increases slightly with Pr addition. Specimens containing 0.075% mol Pr show high giant permittivity (about 30,000) at 540 ºC.
Preparation and characterization of solid electrolyte compounds consisting of doped lanthanum gallate and yttria stabilized zirconia
2019 - FUJIMOTO, T.; MUCCILLO, E.
Ionic conductivity of Sr- and Mg-doped lanthanum gallate with La1.55Sr0.55Ga3O7+delta addition
2018 - FUJIMOTO, T.G.; MUCCILLO, E.N.S.; CARVALHO, L.A.
Sr- and Mg-doped lanthanum gallates are solid electrolytes with ionic conductivity higher than that of the traditional yttria-stabilized zirconia. Moreover, doped lanthanum gallates exhibit wide electrolytic domain and good chemical stability. The combination of their properties turns this compound a promising candidate for application in solid oxide fuel cells operating at intermediate temperatures (550-750°C). In this work, small amounts of La1.55Sr0.55Ga3O7+δ was added to doped lanthanum gallate and the effects of the additive on electrical properties of the base material were investigated by the impedance spectroscopy technique. The X-ray diffraction patterns of sintered specimens show the characteristic reflections of the perovskite-type phase, along with low-intensity diffraction peaks of the commonly detected impurity phases. The impedance spectroscopy diagrams reveal the high-frequency arc due to the bulk resistivity besides a strong overlap of the grain boundary arc with that of the electrode. The grain resistivity decreases for increasing amounts of La1.55Sr0.55Ga3O7+δ.