Li Longtu

Low temperature sintering of lead magnesium nickel niobate zirconate titanate (PMN-PNN-PZT) piezoelectric ceramic, with high performances

Abstract Low temperature sintering of quarternary system lead magnesium nickel niobate zirconate titanate (PMN-PNN-PZT) piezoelectric ceramics has been investigated. This ceramic with proper additives could be sintered at about 900°C and exhibited excellent piezoelectric properties: Kp = 0.61–0.65, Qm ≥ 1000, ϵT/33/ϵ0 = 2300–2800, d 33 = 430–465 × 10−12 C/N, tgδ ≤ 50 × 10−4, ρ = 7.9–8.01 g/cm3. The microstructure and sintering mechanism of the materials has been studied by means of SEM and TEM.

Lead zirconate titanate ceramics and monolithic piezoelectric transformer of low firing temperature

Abstract The binary system lead zirconate titanate (PZT) ceramics and monolithic piezoelectric transformer (MPT) have been investigated. The sintering temperature of PZT ceramic could be reduced from about 1250°C to about 960°C by the addition of a small amount of lower melting frit which is composed of B2O3-Bi2O3-CdO. The properties of the material are: Kp = 0.52 − 0.58. Qm = 1000, ϵ T/33/ϵ0 = 800 − 1100, tgδ = 50 × 10−4 ρ = 7.56 − 7.64 g/cm3. The Ag/Pd = 80/20 internal electrodes of MPT were cofired with ceramic green sheets at a temperature of about 960°C. The experimental results show that MPT has very high voltage step up ratio, lower driving voltage. The alternating current no-load voltage step up ratio of 9000 has been obtained. It is 30–40 times higher than that of the conventional single layer piezoelectric transformer.

Low temperature sintering of PZT ceramics

Abstract Low temperature sintering of PZT piezoelectric ceramics has been studied. The sintering temperature of PZT ceramics could be reduced from about 1250°C to about 960°C by the addition of small amounts of lower-melting frit (B2O3-Bi2O3-CdO). The electrical properties obtained were: Kp = 0.52–0.58, Qm ≥ 1000, ϵ T/33/ϵ0 = 800–1000, tg δ ≤ 50 × 10−4. The microstructure, sintering mechanism and the effects of additions have been analyzed by means of SEM, EPMA, XPS, etc. A monolithic piezoelectric transformer using this material has been made.

Sol-gel derived BaTiO3 thin films with embedded silver nanoparticles : Preparation and dielectric properties

Abstract Composites of ferroelectric BaTiO3 thin film with embedded silver nanoparticles have been produced by the sol-gel process. The structure of the composite and the formation process of the silver particles were studied by x-ray diffraction and transmission electron microscopy. The dielectric properties of the composite were measured and a dependence in reverse to percolation law was shown.

Magnetic properties of non-stoichiometric Y-type hexaferrite

Abstract The magnetic characterization of Y-type hexaferrites series with Ba2Zn0.6Co0.6Cu0.8Fe12−xO22−1.5x has been investigated. Y-type polycrystalline hexaferrite powders were prepared by the solid-state reaction method. The samples were characterized by X-ray diffraction and scanning electron microscopy. An investigation of the magnetic permeability over a wide frequency range was done using an impedance analyzer. Experimental results show that cation deficiency leads to a decrease in sintering temperature. It is indicated that Y-type hexaferrite samples with proper cation deficiency sintered at low temperatures possess excellent magnetic properties for application.

Effect of phosphor doping on the microstructure and dielectric properties of barium titanate ceramics

Abstract The effect of phosphor doping on the sintering behaviour, microstructure and dielectric properties of BaTiO 3 has been investigated. Diisopropyl phosphinate is added to high-purity BaTiO 3 powder prepared by the wet chemical method with a final amount of 0.14 wt.% P 2 O 5 with respect to the BaTiO 3 . Phosphor-doped BaTiO 3 ceramics with a high density and uniform grain size have been produced by using wet processing and pressureless sintering without any binder. A scanning electron microscope, thermometric analysis, X-ray diffraction and an impedance analyser have been used to determine the microstructure as well as the dielectric properties. The phosphor cations can form a liquid phase belonging to the ternary system BaO-TiO 2 -P 2 O 5 , leading to the formation of BaTiO 3 ceramics with high density at low temperature. Phosphor-doped BaTiO 3 ceramics with a high density of 96% D th are obtained by sintering at 1200°C with a soaking time of 2 h. The dielectric constants of samples sintered at 1150 and 1200°C are as high as 6100 and 5500, respectively; the Curie temperature of samples decreases with decreasing sintering temperature. Doping with a small amount of phosphor can improve the sintering and dielectric properties of BaTiO 3 ceramics.

Enhancement of positive temperature coefficient resistance effect of BaTiO3-based semiconducting ceramics caused by B2O3 vapor dopants

Abstract The positive temperature coefficient resistivity (PTCR) effect of semiconducting BaTiO3 ceramics can be remarkably influenced by both dopants and ceramic processing. The behavior of B2O3 as vapor dopants was studied in this paper. It was found that the PTCR effect was enhanced distinctly, while the room temperature resistance also increased.

A study of V-shaped PTC behaviour of Sr0.4Pb0.6TiO3 ceramics

Abstract Yttrium-doped Sr 0.4 Pb 0.6 TiO 3 ceramics were prepared at relatively low sintering temperature using conventional sintering technology. The sintered ceramics exhibit novel NTC–PTC composite effects. The influences of doping PbO and SiO 2 on the properties of Sr 0.4 Pb 0.6 TiO 3 ceramics were compared. It was found that suitable PbO additives reduce the room-temperature resistivities ( ρ RT ) of Sr 0.4 Pb 0.6 TiO 3 ceramics and weaken their NTC effects, but the effect of doping SiO 2 is reverse. The XRD analyses show that SiO 2 additives can cause Pb 2+ ions segregating out from Sr 0.4 Pb 0.6 TiO 3 lattices and form PbO·SiO 2 phase. It is estimated that the strong NTC effects of Sr 0.4 Pb 0.6 TiO 3 ceramics should be closely related to the Pb 2+ immigration. The domain structure, morphology and compositional distribution of Y-doped Sr 0.4 Pb 0.6 TiO 3 ceramics were investigated using TEM, SEM and EDAX respectively. The results of EDAX indicate that the Pb/Sr ratio on the grain boundaries is slightly lower than that in the grains. According to the results, the V-shaped PTC behaviors of (Sr,Pb)TiO 3 ceramics are discussed.

Influence of manganese on PTCR effect in BaTiO3-based ceramics doped with Bi2O3 vapor

Abstract The positive temperature coefficient resistance (PTCR) effect of BaTiO 3 -based ceramics is strongly influenced by the doping of donor and acceptor. Some 3d acceptors such as Mn, Fe, Cu can enhance it greatly, whereas this is not the case for the other acceptors such as K, Na, Ni, Mg. The effect can also be enhanced by the doping of Bi 2 O 3 vapor during sintering in BaTiO 3 -based ceramics; in this case, the enhancement of PTCR effect of the sample codoped with manganese is much greater than that only doped with donor. This is because that excess donor can be compensated by codoped manganese and form more stable composite trap centers, and the PTCR effects can be enhanced more distinctly.

Mössbauer study on valency state of iron ions in Pb(Fe12Nb12)O3 ceramics

Pb(Fe12Nb12)O3 (PFN) ferroelectric ceramics with pure perovskite phase were prepared by the direct formation method. Mossbauer study of iron in PFN ceramics indicated that Fe3+ and Fe2+ ions could coexist in undoped PFN ceramics, and only Fe3+ ions existed in PFN ceramics doped with MnO2. All Fe3+ and Fe2+ ions were in the lower spin state and in [FeO6] coordination state.