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The thickness of BaTiO3 tape castings as function of the slip system
Román Nava,Sophie Guillemet-Fritsch,Juan Aguilar-Garib,Edgar Reyes,Bernard Durand 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.2
One of the most popular techniques in the fabrication of multilayer ceramic capacitor (MLCC) is tape casting, which requires the preparation of a slip that could be either solvent or water-based. A requirement of MLCC miniaturization has pushed improvement of this technique up to the point of fabricating ceramic films below 10μm. However, less information on a direct comparison of aqueous and non-aqueous slips systems using BaTiO3 for dielectric tapes below 3.5 μm is available in the literature. Therefore, solvent and water-based systems were studied in this research aimed to weight the different factors on the thickness reduction; in particular the relation between slip viscosity and ceramic tape thickness was established for both slips formulations. It was found that viscosity below 100 mPa·s is a not a general rule since there is an important influence of the solvent medium; nevertheless adhesion tape-substrate plays an important role over the thinning of water-based formulations. The slip viscosity is defined by the dispersant type of aqueous systems and the binder of non aqueous systems, while reduction of the powder size is more sensitive to the solvent medium as for polar/non –polar mixtures. Ceramic tape homogeneity is strongly affected by the presence of hard aggregation and should be accounted for with the use of nanoparticles. A condition was also demonstrated where low viscosities and thinner layers are related.
Tawfik Al-Naboulsi,Madona Boulos,Christophe Tenailleau,Pascal Dufour,Mirvat Zakhour,Sophie Guillemet-Fritsch 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.8
The current work aims to reduce the energy required to obtain a high quality barium titanate nanocrystals via solid-statereaction. In order to achieve this challenge, Ba(NO3)2 and TiO2 were mechanically activated by high-energy ball milling, andthen heat treated at moderate temperature (600 oC). When stoichiometric mixture was used, the formation of BT and minorBaCO3 and TiO2 impurities was observed. The use of Ba(NO3)2 excess leads to the formation of BT and a minor BaCO3impurity. A simple acid wash treatment was used to remove the carbonate impurity and to provide a high purity BT. Thepowders were characterized by XRD, BET, Raman spectroscopy, and SEM-FEG. Spark Plasma Sintering (SPS) technique wasused to get the dense nanoceramics. These materials show, at room temperature and at 1 kHz, colossal permittivity (ε = 105)associated with low dielectric loss (tg δ = 0.07).
Han, HyukSu,Lee, Jae Seok,Ryu, Jeong Ho,Kim, Kang Min,Jones, Jacob L.,Lim, Jiun,Guillemet-Fritsch, Sophie,Lee, Han Chan,Mhin, Sungwook American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.25
<P>Hopping motions in cobalt manganese spinel oxides with high cobalt concentration (CoxMn3-xO4, 2.3 <= x <= 2.7) are investigated in order to clarify the origin of unusual electrical behaviors as negative temperature coefficient (NTC) thermistors. Based on the resistance versus temperature (R-T) characteristics, hopping conduction mechanisms in MCO compounds (x = 2.3 and 2.5) are attributed to variable range hopping (VRH) motion with a parabolic distribution of the density of states (DOS) near the Fermi level. However, when Co content increases up to 2.7, transition in the hopping motion occurs from VRH to the nearest neighboring hopping (NNH) motion, which can be responsible for a huge increase of the resistance accompanied by decrease of the factor of thermal sensitivity (B value) in MCO compounds (x = 2.7). Also, hopping distance and activation energies for MCO (x = 2.3 and 2.5) compounds following VRH conduction are calculated as a function of temperature, indicating that higher B value observed in MCO (x = 2.5) compound is due to the larger hopping distance compared to that of MCO (x = 2.3) compound.</P>