Finite element modeling on the effect of intra-granular porosity on the dielectric properties of BaTiO 3 MLCCs

The effect of porosity on the electrical properties of BaTiO3-based MultilayerCeramic Capacitors (MLCCs) is studied. A dense ceramic prepared via powderfrom a solid-state processing route is compared against a ceramic that containsintra-granular pores from powder prepared via hydrothermal processing. Finiteelement models are created to contain intra-granular pores, solved and analyzed toshow an increase in the electric field and current density surrounding the pores.For single-pore and two intra-pore arrangements, the electric field is enhanced bya factor of~1.5 and 2.5, respectively, when compared to a fully dense (pore-free)material. For ceramics with equivalent density, the number of pores dramaticallyalters the electrical response. For a system containing 100 pores, the electric fieldcan increase at least fourfold, therefore facilitating a possible starting route forelectrical breakdown of the grain. These results are compared to the Gerson-Mar-shall model, typically used in the literature for the calculation of the breakdownstrength due to porosity. The results highlight the need to include the effect ofadjacent pore interactions. Although studied here for BaTiO3-based MLCC’s theresults are applicable to other devices based on ceramics containing porosity

Interaction of Gold Nanoparticles in Barium Titanate Thin Films

A novel approach to control the grain size of oxide thin film materials has been investigated. Perovskite BaTiO3 shows interesting grain structures when deposited on gold predeposited, (111)-oriented, singlecrystal SrTiO3 substrates. Solid oxide films grow epitaxially on patterned seed layers and show variations in grain size relative to the films deposited on SrTiO3 directly.Comment: 14 pages, 4 figure

Properties of lanthanum doped BaTiO3 produced from nanopowders

Pure and barium titanate (BT) powders doped with different lanthanum concentration were prepared by the polymeric precursor method (Pechini process) which was carried out as a three-stage process from organometallic complexes. Sintering of pressed powders was performed at 1300 8C for 2, 4 and 8 h. XRD analysis showed cubic BT powders with crystallite sizes between 20 and 25 nm and tetragonal crystal structure of BT ceramics. The influence of sintering time on grain growth was fairly obvious. It was found that lanthanum doping has significant effect on powders particle size and ceramics grain size. The influence of lanthanum concentration on grain size inhibition, improving the dielectric properties of BT ceramics was detected. The relation between sintering time, grain size, structure and electrical properties of the BT ceramics was analyzed

History and challenges of barium titanate: Part II

Barium titanate is the first ferroelectric ceramics and a good candidate for a variety of applications due to its excellent dielectric, ferroelectric and piezoelectric properties. Barium titanate is a member of a large family of compounds with the general formula ABO3 which is called perovskite. Barium titanate can be prepared using different methods. The synthesis method depends on the desired characteristics for the end application and the method used has a significant influence on the structure and properties of barium titanate materials. In this review paper, in Part II the properties of obtained materials and their application are presented

Screen printed PLZT thick films prepared from nanopowders

The gap between the bulk materials and thin films can be filled with thick films suitably designed and appropriate processed. Thick films of complex system like lead-lanthanum-zirconium titanate (PLZT) is difficult to produce by simple solid-state reaction keeping compositional homogeneity and optimal grain size distribution. In the present work, PLZT thick films were fabricated by screen-printing technique from nanosized powders obtained through soft chemistry by polymeric precursor method. Thick film paste was obtained by mixing PLZT fine powders and organic vehicle. The upper and bottom electrodes based on Ag-Pd and functional component based on PLZT were screen-printed on alumina substrate and after that annealed in air atmosphere. The powder morphology, microstructure, dielectric and ferroelectric properties of 9.5/65/35 PLZT thick films were analysed. (c) 2007 Elsevier Ltd. All rights reserved

The impact of functional electrical stimulation (FES) on freezing of gait (FOG) in patients with Parkinson's disease

International audiencePatients with Parkinson's disease (PD) frequently exhibit problems with gait initiation, maintaining rhythmicity of the gait, turning, and may suffer from motor blocks, i.e., freezing of gait (FOG). All these issues contribute to higher risk of stumbling and falling. In this study, we tested the influence of functional electrical stimulation (FES) on gait in 9 patients with PD with history of freezing episodes. Patients were walking along the given path comprising standing up from the chair, passing through narrow doorways and turning. Besides regular walking, protocol also comprised walking while carrying tray with glass of water (dual-tasking). Patients' peroneal nerve of the leg which was estimated to be from the weaker side was stimulated during the swing phase in moments when gait "normal" pattern was impaired. Stimulation was triggered automatically based on heel switch placed in the shoe. Gait sequences with and without FES were recorded successively, and these gait patterns were compared afterwards. Results showed that FES decreased duration of double support phase and variability of stride duration and stride length. While stimulated, two patients did not experience motor blocks in a few places along the path where they otherwise had problems with FOG

Structure and Properties of Barium Bismuth Titanate Prepared by Mechanochemical Synthesis

Bi4Ti4O15 [BBT], a member of Aurivillius bismuth-based layer-structure perovskites, was prepared from stoichiometric amounts of BaTiO3 [BT] and Bi4Ti3O12 [BIT] obtained via mechanochemical synthesis. Mechanochemical synthesis was performed in air atmosphere in a planetary ball mill. BBT ceramics were sintered at 1100C for 4 h without pre-calcination step within heating rate 10C/min. The formation of phase and crystal structure of BT, BIT and BBT were approved using X-ray analysis. The morphology of obtained powders and microstructure were exhamined using scanning electron microscopy. The electrical properties of sintered samples were carried out

Lead-free BaBi4Ti4O15 ceramics: Effect of synthesis methods on phase formation and electrical properties

The processing of ferroelectric BaBi4Ti4O15 (BBT) ceramics from powders prepared by conventional solid state reaction (SSR) and mechanochemical activation (MA) has been investigated. It was shown that MA synthesis reduces the synthesis temperature of BBT powders, leading to smaller particles with reduced anisotropy and consequently to smaller grain size of ceramics. Dielectric properties were investigated in a wide range of temperatures (20-800 degrees C) and frequencies (1.21 kHz to 1 MHz). The relative dielectric permittivity at Curie temperature was higher for solid state obtained ceramics than for the mechanically treated ones. The conductivity of sintered samples was studied, suggesting decreasing of conductivity of BBT-MA in comparison with BBT-SS ceramics. The influence of the grain and the grain boundaries contribution to the dielectric behavior in both ceramics was analyzed through impedance spectroscopy. A well-defined ferroelectric hysteresis loop was obtained for both samples. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved