TATIANE CRISTINA PORFÍRIO
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Artigo IPEN-doc 24778 Thermal and electrical properties of CaCu3Ti4O12 synthesized by soft chemistry route2018 - PORFIRIO, T.C.; MUCCILLO, E.N.S.Calcium copper titanate powders were synthesized by a soft chemistry route, aiming to establish a cost-effective solution method to obtain sintered ceramics with giant electric permittivity (ε′) and low dissipation factor (tanδ). Powders and sintered pellets were characterized by several techniques. The thermal decomposition behavior of the porous foam evidences that a hydroxycitrate was formed below 200 °C. Single cubic perovskite-type phase was obtained after calcination of the precursor powder at 700 °C for 5 h. Negligible mass loss occurs above 400 °C. During heating the precursor material, CuO is the first crystallized phase. A giant ε′ and low tanδ are obtained after sintering. The extension of the thermal window of ε′ is wider than those of powders prepared by other methods.Artigo IPEN-doc 23559 Effects of LiF addition on microstructure and dielectric properties of CaCu3Ti4O12 ceramics2016 - PORFIRIO, T.C.; MUCCILLO, E.N.S.The effects of small amounts of lithium fluoride sintering aid on the microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics were investigated. CCTO polycrystalline ceramics with 0.5 and 1.0 mol% LiF, and without additive were prepared by solid state synthesis. Good densification (>90% of the theoretical density) was obtained for all prepared materials. Specimens without the sintering aid and sintered at 1090 °C exhibit secondary phases as an outcome of the decomposition reaction. The mean grain size is controlled by the amount of LiF in specimens containing the additive. Impedance spectroscopy measurements on CaCu3Ti4O12 ceramics evidence the electrically heterogeneous nature of this material consisting of semiconductor grains along with insulating grain boundaries. The activation energy for grain boundary conduction is lower for specimens prepared with the additive, and the electric permittivity reached 53,000 for 0.5 mol% LiF containing CCTO.Artigo IPEN-doc 20887 Influence of lithium disilicate addition on the dielectric properties of chemically synthesized CaCusub(3)Tisub(4)Osub(12)2015 - PORFIRIO, T.C.; MUCCILLO, E.N.S.The effects of the method of synthesis along with the introduction of a sintering aid on the electric and dielectric properties of CaCu3Ti4O12 were investigated in detail. The mixed oxide with perovskite structure was synthesized by the coprecipitation method. Polycrystalline specimens were prepared by adding 0.5 mol% Li2Si2O5 to the mixed oxide followed by sintering in the 1000–1100 C range for 12 h. A high density value was obtained for sintering at a temperature as low as 1000 C. Average grain sizes of sintered specimens are of the same order of magnitude as those of specimens prepared by the same method without the additive. The activation energy values for electric conduction were found to be 0.1 eV (grain) and varying from 0.4 to 0.6 eV (grain boundary). The dielectric properties are similar to those of specimens without the additive. The overall results evidence the possibility of reduction of the sintering temperature by about 100 C with the introduction of a small amount of lithium disilicate while keeping the dielectric properties of pure CaCu3Ti4O12.Artigo IPEN-doc 10228 Synthesis, sintering and impedance spectroscopy of 8 mol percent yttria-doped ceria solid electrolyte2004 - TADOKORO, S.K.; PORFIRIO, T.C.; MUCCILLO, R.; MUCCILLO, E.N.S.