Renzheng Chen

Structure, sintering behavior and dielectric properties of silica-coated BaTiO3

Abstract Silica was homogeneously coated on the surface of barium titanate (BaTiO 3 , BT) fine particles via sol–gel method. The thickness of silica film was about 5 nm. High-resolution transmission electron microscope (HRTEM) investigation and energy dispersion spectrometry (EDS) analysis proved that there was silica coated on BaTiO 3 . The coating mechanism is that after BaTiO 3 hydrolyzed slightly, Na 2 SiO 3 gelatinized on the surface of TiO 2− x . Compared with pure BaTiO 3 , the coating process can improve sintering behavior and flatten temperature coefficients (TC) curves of ceramics based on BaTiO 3 .

Sintering characteristics and dielectric properties of silver-doped PMN-PZN-PT relaxor ferroelectric ceramics

The effects of silver doping on PMN-PZN-PT relaxor ferroelectric ceramics were investigated in order to demonstrate the roles of the inner electrodes in the cofiring of MLCCs, because silver could diffuse from an electrode layer into a dielectric layer. Even if the addition of silver promoted the sintering of ceramics, the insulation resistance and the dielectric properties were changed to a certain extent so that they had a great influence on the reliability of MLCCs. Defect chemistry principles were used to analyze the mechanism of action of silver doping. The relationship of silver migration and microstructural formation was also discussed

Barium titanate coated with magnesium titanate via fused salt method and its dielectric property

Barium titanate fine particles were coated homogeneously with magnesium titanate via the fused salt method. The thickness of the magnesium titanate film is 20 nm, as verified by TEM and XRD. The mechanism of the coating is that: when magnesium chloride is liquated in 800 °C, magnesium will replace barium in barium titanate, and form magnesium titanate film on the surface of barium titanate particles. Ceramics sintered from the coated particles show improved high frequency ability. The dielectric constant is about 130 at the frequency from 1 to 800 MHz.

Synthesis and properties of barium titanate based X7R ceramics by chemical method

Abstract The BaTiO3 powder prepared by chemical method was used to fabricate X7R type ceramics. The effects of grain size, composition of modifier, sintering temperature and dwell time on the microstructure and properties of ceramics were studied systematically. X-ray diffraction, scanning electron microscopy, transmission electronic microscopy, energy dispersive spectroscopy as well as dielectric measurement were used to characterize ceramic samples. A novel temperature stable dielectric material of BaTiO3-based X7R ceramic material sintered at 1240°C∽1260°C has been developed showing dielectric constant up to 4700, TCC less than ±10%, with high resistivity (1012Ω•cm) and high breakdown voltage (10KV/mm). It has been used to fabricate X7R MLCC with dielectric constant over 5000.

Size effect of barium titanate based ceramics sintered in reducing atmospheres

Non-reducible BT-based X7R type ceramic materials with grain size form 100 nm to 400 nm were prepared systematically with high performance using nano-sized BaTiO/sub 3/ powders. The initial grain size of BT powders affects significantly the microstructure and dielectric properties. The dielectric constant could be enhanced by increasing the initial particle size. Using BT powder with size of 250 nm, high density BME-MLCC chip samples (ceramic grain size of 300 nm) were obtained sintered at 1217/spl deg/C, exhibiting high dielectric constant above 3000, and TCC less than /spl plusmn/ 11.5%. with good reliability, meeting the requirement of X7R specification. In nanoceramic X7R BaTiO/sub 3/ sample, clear ferroelectric domain structure was also observed for the first time. The inhomogeneous core-shell microstructure was found in the X7R samples.

The Effect of Different Doping Methods of Sintering Aids on the Barium Titanate Based X7R Ceramics

The barium titanate based X7R ceramics, which are doped with rare earth oxide, Nb2O5, Co3O4 and ZnO-B2O3, could be sintered at a rather low temperature to satisfy the X7R requirements with good permittivity and dielectric loss. In this paper, different doping methods of sintering aids have been used to prepare X7R BaTiO3 ceramics. Samples were sintered at a low temperature and the relationship of doping methods and sintering properties has been concluded.

Dielectric Properties of BaTiO 3 Based Ceramics Prepared from Nano-powders

In this paper, the BaTiO 3 nanoceramics have been fabricated by pressureless sintering for the first time. High purity BaTiO 3 powders in nano-size of 50∼80nm synthesized by wet chemical method were used to fabricate nanoceramics. The addition of an appropriate amount of Nb 2 O 5 and Co 3 O 4 was found to suppress the grain growth, which is normally encountered in the conventional pressless sintering. The effects of Nb 2 O 5 and Co 3 O 4 on the phase structure, microstructure and dielectric properties of the sintered ceramics were investigated. The BaTiO 3 ceramics with the average grain size less than 100nm were achieved after sintering below 1220°C with dielectric constant up to 2000 at room temperature, which is of cubic structure and meets the requirement of X7R specification.

Microstructural and dielectric properties of ceramics based on K/sub 2/Sr/sub 4/Nb/sub 10/O/sub 30/ and BaTiO/sub 3/

The search for dielectric materials with a high dielectric constant and /spl epsiv/ curves with a flat profile is still ongoing. K/sub 2/Sr/sub 4/Nb/sub 10/O/sub 30/-based dielectric ceramics, having the tetragonal tungsten bronze structure (TTB), which display a high permittivity and flat /spl epsiv/ curves meeting the X7R specification. BaTiO/sub 3/-based ferroelectric ceramics are classic dielectric materials for ceramic capacitors. Results were obtained by mixing compounds with closely related structures, such as the tetragonal tungsten bronze (TTB) niobate K/sub 2/Sr/sub 4/Nb/sub 10/O/sub 30/ (KSN) and the perovskite BaTiO/sub 3/ (BT). Phase compositions were analyzed by using XRD and the microstructure was investigated by SEM. The present study explores the dielectric curves /spl epsiv/ of the composition (K/sub 2/Sr/sub 4/Nb/sub 10/O/sub 30/)/sub x//spl middot/(BaTiO/sub 3/)/sub 1-x/ with x = 0.1-0.9 where x means the weight ratio of KSN. The dielectric constant at room temperature is lowest at x = 0.4. When x is between 0.4 and 0.7, /spl epsiv/ curves of the ceramic composites present a linear decrease with the temperature. Two different phases, TTB and perovskite type, are present after sintering.

Study on structure and properties of X7R ceramics based on BaTiO/sub 3/ with high dielectric constants

Microstructures and dielectric properties of BaTiO/sub 3/-based X7R ceramics were studied. The dielectric constant at room temperature is about 4600, and the dielectric loss is 10/sup -2/. The resistance is over 10/sup 12//spl Omega//spl middot/cm and TCC is less than /spl plusmn/15%. Under bias voltage, TCC is less than 13%. Therefore the materials meet EIA X7R specifications. The microstructures were studied by SEM and TEM. Inhomogeneous compositional distributions within the grains were observed that consisted of two main parts, each possessing a different temperature dependence of the dielectric constant. Multilayer capacitors were fabricated and showed outstanding performances. Dielectric constants of 5100 were achieved and components have passed the life test at 125/spl deg/C for 1000 hr.