Jianquan Qi

Ferroelectric characteristics of ytterbium-doped barium zirconium titanate ceramics

Abstract Ferroelectric characteristics of ytterbium-doped barium zirconium titanate (BZT in brief) ceramics have been investigated. It is found that ytterbium dopant greatly influences the dielectric properties of BZT ceramics. With the increase of ytterbium content, the Curie temperature is lowered by three apparent stages identified by the falling “rate”, and the relative permittivity maximum is enhanced and broadened enormously. The diffuseness of the ferroelectric phase transition for BZT is increased monotonously as well. The A/B ratio in perovskite structure plays another important role on the ferroelectric phase transition characteristics for ytterbium doped BZT. The alternation of the substitution preference of ytterbium ions for the host cations in perovskite lattice seems to account for these effects. Thanks to the modifications of ytterbium on BZT, we developed a novel Y5V dielectric material with the room temperature dielectric constant over 23,000, and the dielectric strength higher than 4.0 kV/mm under AC field, which can be used in manufacturing high voltage ceramic capacitors.

Doping behaviors of Nb2O5 and Co2O3 in temperature stable BaTiO3-based ceramics

Abstract The influence of Nb2O5 and Co2O3 on the dielectric constant–temperature characteristic of the Sm2O3, CeO2-doped BaTiO3 system was discussed. It can be concluded that Nb5+, Co3+ will be easier to replace the Ti4+ site by using the Nb2O5–Co2O3 composite oxide than by doping Nb2O5, Co2O3 separately. Increasing Co2O3 amount caused a lower dielectric constant and a higher variation rate. A properly sintering temperature can be helpful to flatten the dielectric constant–temperature curve. The BaTiO3-based ceramics doped with the Nb2O5–Co2O3 composition can be sintered at a temperature as low as 1230–1250 °C, and satisfy the X7R required with a high dielectric constant (e25 °C>4000) and low dielectric loss (tan δ

Direct synthesis of ultrafine tetragonal BaTiO3 nanoparticles at room temperature

A large quantity of ultrafine tetragonal barium titanate (BaTiO3) nanoparticles is directly synthesized at room temperature. The crystalline form and grain size are checked by both X-ray diffraction and transmission electron microscopy. The results revealed that the perovskite nanoparticles as fine as 7 nm have been synthesized. The phase transition of the as-prepared nanoparticles is investigated by the temperature-dependent Raman spectrum and shows the similar tendency to that of bulk BaTiO3 materials. It is confirmed that the nanoparticles have tetragonal phase at room temperature.

The PTCR effect in BaTiO3 ceramics modified by donor dopant

Abstract The PTCR effect of BaTiO 3 -based ceramics is influenced severely by either impurities or the process. The influence of Ce 3+ , Sm 3+ and Yb 3+ on the PTCR effect was studied. In order to exclude other influential factors, the ceramics was only modified by donor dopant using high purity raw materials. It was found that, in each group of these donor doped samples, the RT resistance decreased with donor content in low doping level, after it reaches a minimum, and increases rapidly at high doping level; the PTCR effect decreased with donor content irrespective of the doping level.

Improvement of temperature-stable BaTiO3-based dielectrics by addition of Li2CO3 and Co2O3

Abstract The influence of Co 2 O 3 and Li 2 CO 3 on the dielectric constant-temperature characteristic of the BaTiO 3 –Nb 2 O 5 –La 2 O 3 –Sm 2 O 3 system (BNLS) was studied. The Co element is useful to flatten the dielectric constant-temperature curve at low temperature. Compared with the influence of Co 2 O 3 , Li 2 CO 3 is an effective additive that can improve the dielectric constant of this system at high temperature near the Curie temperature. This is very helpful for this ceramic system to satisfy the requirement of EIA X7R specification on TCC and still keep a relatively high dielectric constant at room temperature. The possible mechanism of the phenomenon was also discussed.

Dielectric properties of barium titanate ceramics doped by B2O3 vapor

The effects of B2O3 vapor doping on the dielectric properties of barium titanate ceramics were studied. After the doping, the Curie point of BaTiO3 ceramics was increased from 128 °C to 130 °C and the maximum dielectric constant was considerably increased. X-ray diffraction showed that both the grain lattice parameters and the tetragonality were increased by the boron oxide vapor doping. It was proposed that boron interstitial was introduced into the grain lattice of barium titanate ceramics by B2O3 vapor doping and the dielectric properties were thus obviously changed.

Fabrication of CuO nanoparticle interlinked microsphere cages by solution method

Here we report a very simple method to convert conventional CuO powders to nanoparticle interlinked microsphere cages by solution method. CuO is dissolved into aqueous ammonia, and the solution is diluted by alcohol and dip coating onto a glass substrate. Drying at 80 °C, the nanostructures with bunchy nanoparticles of Cu(OH)2can be formed. After the substrate immerges into the solution and we vaporize the solution, hollow microspheres can be formed onto the substrate. There are three phases in the as-prepared samples, monoclinic tenorite CuO, orthorhombic Cu(OH)2, and monoclinic carbonatodiamminecopper(II) (Cu(NH3)2CO3). After annealing at 150 °C, the products convert to CuO completely. At annealing temperature above 350 °C, the hollow microspheres became nanoparticle interlinked cages.

Thickness dependence of in-plane dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 thin films epitaxially grown on LaAlO3

The authors have studied the effects of film thickness on the lattice strain and in-plane dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 thin films epitaxially grown on LaAlO3 (001) single crystal substrates. With increasing film thickness from 20to300nm, the in-plane lattice parameter (a) increased from 0.395to0.402nm while the out-of-plane lattice parameter (c) remained almost unchanged, which led to an increased a∕c ratio (tetragonality) changing from 0.998 to 1.012 and consequently resulted in a shift of Curie temperature from 306to360K associated with an increase of the in-plane remnant polarization and dielectric constant of the film.

Dielectric properties and abnormal C-V characteristics of Ba0.5Sr0.5TiO3–Bi1.5ZnNb1.5O7 composite thin films grown on MgO (001) substrates by pulsed laser deposition

Highly c-axis oriented Ba0.5Sr0.5TiO3-based composite thin films were grown on MgO (001) single-crystal substrates by pulsed laser deposition and the in-plane dielectric properties of the films evaluated. X-ray diffraction characterization revealed a good crystallinity. The dielectric constant and loss were found to be 200 and 0.001–0.007 at room temperature, respectively. The butterfly-shaped C-V characteristic curve evidenced an enhanced in-plane dielectric tunability of >90% in the films at 1MHz under a dc bias field of 0.8MV∕cm. A brief discussion is given on the abnormal C-V curves. Various tunable microwave applications of Ba0.5Sr0.5TiO3–Bi1.5ZnNb1.5O7 composite thin films are expected.

Difference of Bi2O3 doping effect between vapor process and solid process on Ba1−xSrxTiO3 semiconducting ceramics

Doping process is very important for the properties of materials. The properties of the Ba1−xSrxTiO3 positive temperature coefficient resistance (PTCR) ceramics, in which Bi2O3 was doped by a new process called vapor doping method, have improved greatly. The resistance jumping can be increased to over eight magnitude orders and the temperature coefficient can be obtained as high as 40%/°C. While this was not the case by conventional solid doping method, the PTCR effect of the sample doped with solid Bi2O3 decreased with the increasing of doping content. The complex impedance analysis revealed that the change of grain boundary character by the doping with vapor Bi2O3 would be responsible for the enhancement of the PTCR effect of the Ba1−xSrxTiO3 ceramics.