Materials Science Forum Vols. 475-479

Abstract: Lead-free piezoelectric ceramics have received more attention due to the environmental protection of the earth. Niobate ceramics such as NaNbO3 and KNbO3 have been studied as promising Pb-free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, Spark Plasma Sintering (SPS) was applied to the sintering of Na0.5K0.5NbO3 ceramics, whose powder was synthesized by the conventional oxide mixing method. No loss of sodium and potassium were found in the SPS sintering process, by which the density of the K0.5Na0.5NbO3 solid solution ceramics was raised to 4.21g/cm3 (>93% of the theoretical density) at temperatures as low as 920°C. The crystal phase of the Na0.5K0.5NbO3 is an orthorhombic structure. The piezoelectric parameter (d33) of the K0.5Na0.5NbO3 ceramics reached 49 pC/N.

Abstract: High purity BaTiO3 single crystal was aged below its Curie temperature for different times. The reverse transformation (from tetragonal to cubic) temperature was measured precisely by differential scanning calorimetry (DSC). It was observed that the reverse transformation temperature increased with increasing aging time, indicating ferroelectric phase became stable with aging. This behavior is the same as found in ferroelastic alloys. The origin of the stabilization effect in ferroelectric single crystals was discussed with respect to the distribution of point defects.

Abstract: Ferromagnetism in La-doped single crystal CaB6 is interesting because it has no partially filled d- or f- orbits in CaB6. In this paper, we have investigated the relationship between the ferromagnetic properties with the La content in CaB6 polycrystalline ceramics prepared by redox method. Contrary to the single crystal results, we found that there is no direct correlation with the level of La substitution in ceramics samples Ca1-xLaxB6 (0 £ x £ 0.03). Instead we have shown that it is related to Fe impurities. Our results show it is important to consider the magnetic impurities in discussing the weak ferromagnetism in borides.

Abstract: Antibacterial titanate whiskers were synthesized by calcination of titanium dioxide with potassium carbonate, following by ion-exchanged and immobilized with Ag+ and Cu2+. The pretreatment conditions for whiskers synthesis were investigated; the microstructures of as-prepared whiskers were characterized by XRD and SEM. The antibacterial performance of cation-doped titanate whiskers was tested and evaluated by Escherichia Coli. and staphylococcus aureus.

Abstract: Carbonate precursor of Eu3+ doped Sr2CeO4 is obtained from a mixed solution of strontium, cerium and europium nitrate using ammonium carbonate as precipitant. Calcining the carbonate precursor at different temperatures, the Eu3+ doped Sr2CeO4 phosphor is synthesized. The phase purity of the material is closely related with the calcination temperature, and the phosphor with high purity can be achieved after the precursor annealed at 1200°C. The photoluminescence performance for Eu3+ doped Sr2CeO4 depends on the concentration of Eu3+. The excitation and emission reveal efficient energy transfer from Ce4+ to Eu3+, making the emission light from blue-white to red-white, further to red as the Eu3+ concentration gradually changes from low concentration (1 mol%) to high concentration (10 mol%).

Abstract: The multilayer composites were prepared by cofiring Pb(Ni1/3Nb2/3)O3-based ferroelectrics and NiCuZn ferrite using tape casting processes. The interface and grain growth of the composites were investigated. The results show that the sintered interface of composites is solid, continuous with no delamination and cracks, which should be attributed to the chemical compatible of the two materials. The grain growth of ferroelectrics adjacent to the interface is different from that far from the interface. It should attribute to Fe3+ diffused from the ferrite to ferroelectrics and soluted into the perovskite lattice. The difference factor dD is proposed to describe the microstructure difference between the interface and the inner parts.

Abstract: The polycrystalline Dy3+ doped PLZT ceramics with compositional formula [Pb0.88 (La1-xDyx)0.12](Zr0.40Ti0.60)O3, were prepared by hot-pressed method. Effects of Dy3+ substitution on structural and optical properties were report here. All the samples have single phase with tetragonal structure, and the tetragonality was increased with content increased. As Dy3+ content increased, the optical transmission was found to decrease, and the refractive index was raised slightly.

Abstract: Bipolar electric fatigue in antiferroelectrics of the lead zirconate titanate stannate ceramics family was investigated. Variations in strain hysteresis loops and damages in microstructure of the materials due to the electric cycling were analyzed. The materials showed symmetric or asymmetric suppression of strain hysteresis loop, normal or diffuse AFE-FE phase transition and intact or damaged microstructure after 5×10-7 cycles, indicating a strong composition dependent fatigue effect and the corresponding mechanism. In general, the antiferroelectric materials exhibited much higher fatigue resistance than ferroelectric ceramics reported previously.

Abstract: Reaction between nanometer γ-Al2O3 and H3PO4 to form AlPO4 by hydro-thermal method was studied. The microstructure of the reaction product was examined by SEM (scanning electronic microscope). The phase transformation of AlPO4 was investigated by DSC (differential scanning calorimeter) and XRD (X-ray Diffraction). The relative dielectric constant and dielectric dissipation factor of different kinds of aluminum phosphates were measured. Results of the study led to the optimal parameter of the reaction and showed that aluminum phosphate is a good matrix to make functional ceramic-matrix composites.

Abstract: (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ((1-x)PMN-xPT, PMN-PT) with composition near the morphotropic phase boundary (MPB) were prepared by the columbite precursor method and the rutile precursor method respectively. Attention has been focused on the influence of process on microstructure of PMN-PT ceramics. The results show that the average grain size of ceramics is insensitive to composition for both above processes. The refinement and homogeneity on grain size in the rutile precursor method is better than that in the columbite precursor method.