Pu Yongping

Influence of Rare Earths on Electric Properties and Microstructure of Barium Titanate Ceramics

Abstract The influence of rare earths on electrical resistivity and microstructure of barium titanate ceramics doped with rare earth ions Y, Dy, Ho, Er and Y at the concentrations of x = 0.001 × 0.01 was investigated by the means of X-ray diffraction, scanning electron microscopy and electric properties testing. The results showed that a dramatic decrease in resistivity occurred at the concentration of 0.3% of La-doped sample. However, the range of concentration for semiconducting samples doped with Dy, Ho, Er and Y was wider, especially for Y-doping. The experimental results indicated that below the critical concentration of Dy, Ho, Er and Y, the substitution took place in the barium sublattice with electronic compensation, above the critical concentration, gradually the rare earth ions began to substitute for titanium. As for Hodoped BaTiO 3 ceramic, the resistivity jump (PTCR effect) near the Curie temperature was the highest in case of lower dopant concentration of 0.3%. Fine-grained structure of sample doped with 0.6% Dy led to the increasing of breakdown electric field strength and dielectric constant of ceramic samples. In contrast, coarsed-grained structure of sample doped with 0.3% Dy showed semiconducting property.

Study of reoxidation in heavily La-doped barium titanate ceramics

The ceramic samples of (1-x)BaTiO3+1/2xLa2O3+(2+x)mol%TiO2 (0.003?x?0.15) were prepared by sintering in reducing atmosphere of H2, subsequently reoxidized in air. The effect of heavily La dopant on the resistivity and microstructure of the reoxidized samples were investigated by means of scanning electron microscopy and electric properties testing. The results show that the critical concentration of La-doped samples increased obviously compared with the samples sintered in air. The grain size decreased with the increase of La-donor content. The positive temperature coefficient resistivity effect of the sample increased when a change reoxidizing temperature range of 600?C ~1200?C. The maximum of ?max/?min ratio was ~700 at the reoxidizing temperature of 1100?C when x=0.8mol%.

Influence of Liquid Phase on Grain Growth of Ba0.998La0.002TiO3 Ceramics

Abstract The influence of liquid phase on grain growth of Ba 0.998 La 0.002 TiO 3 ceramics with a different concentration of excess of 2.0% TiO 2 sintered at a temperature of 1350 °C was investigated. The results showed that a small amount of Si and P, which came from the raw materials of BaCO 3 and TiO 2 powders during the liquid phase sintering of Ba 0.998 La 0.002 TiO 3 ceramics. On one hand, the liquid phase must present during grain growth, on the other hand, BaTiO 3 grains must be dissolved, then precipitated from the liquid phase during the process of dissolution-precipitation, otherwise, the grain growth would be inhibited. The liquid phases of Ba 6 Ti 17 O 4 and Ba 2 TiSi 2 O 8 promoted grain growth due to high solution of BaTiO 3 grains in the liquid phases. Compared with that, Ba 2 Ti 2 SiP 2 O 13 liquid phase inhibited the process since BaTiO 3 grains could not dissolve into the phase, consequently the samples show insulating.

Influence of Ti/Ba Ratio on the Positive Temperature Coefficient Resistance Characteristics of Mn-doped Semiconducting BaTiO3 Ceramics

Influence of Ti/Ba ratio on the positive temperature coefficient resistance characteristics of Mn-doped semiconducting ceramics of (Ba0.997La0.003)(Ti x − y Mn y )O3 (0.97 ≤ x ≤ 1.02, 0.0003 ≤ y ≤ 0.0008) sintered in reducing atmosphere of N2 and reoxidized in an atmosphere with low oxygen partial pressure were investigated. The grain size of BaTiO3 ceramics strongly depends on A/B molar ratio because liquid phase promotes grain growth during sintering. The results show that semiconducting BaTiO3 ceramics fired in a reducing atmosphere and reoxidized at a low temperature of 850°C in air show better PTCR characteristics. However, Mn-doped BaTiO3 ceramics with (Ti + Mn/Ba + La) = 1.01 exhibited remarkable PTCR characteristics with a resistance jump of three order of magnitude.

Effect of CeO2 Addition on the Microstructure and Dielectric Properties of BaTiO3 Co-Doped with Nb and Fe

The CeO2-doped BaTiO3-Nb2O5-Fe2O3 ceramics were sintered at different temperatures and the effects of the additive on the microstructures and dielectric properties were studied by X-ray diffraction (XRD), SEM, DSC and LCR analyzer a respectively. The results indicated that the CeO2 additive could accelerate the pore elimination, shorten the sintering time, shift the Curie temperature to higher temperatures and enhance the density for BaTiO3-Nb2O5-Fe2O3 ceramics. The well development of microstructure promoted by the additives can result in the improvement of the dielectric constant. When the doping concentration of CeO2 was 0.20 mol%, the relative density of the sample sintered at 1300 °C for 2 h can reached to 93.4% and the relative dielectric constant reached to ∼4000. As a result, a novel material is developed in the system, which is very promising for practical use in multi-layer ceramic capacitors (MLCCs).

Investigation of Microstructure and Dielectrical Properties of Highly Sm2O3-Doped Bismuth Titanate Ceramics

High Sm2O3-doped Bi4Ti3O12 (BIT)-based ceramics were prepared by solid-state reaction method. The influence of the concentration of Sm2O3-doping on the crystal phase, the microstructure and dielectrical properties of the samples were investigated by XRD, SEM, Agilent 4284A and P-E test system. The results showed that the new compound Bi0.56Sm1.44Ti2O7 was observed when the concentration of Sm2O3-doping was 12.0mol%. The dielectric studies revealed that the dielectric loss (tanδ) of the ceramics reduced to 0.003 when the concentration of Sm2O3-doping was in a range of 3.0∼12.0mol%. The Curie temperature (T c) of each sample gradually moved toward lower temperature as the amount of Sm2O3 was increased up to 12.0mol%.