Key Engineering Materials Vols. 434-435

Abstract: Bi4Ti3O12 (BTO) and Bi3.25La0.75Ti3O12 (BLT) ferroelectric thin films were deposited on Pt/Si substrates by RF magnetron sputtering with Bi4Ti3O12 (BTO) and Bi3.25La0.75Ti3O12 (BLT) targets with 50-mm diameter and 5-mm thickness. The microstructure and ferroelectric properties of thin films were investigated. The grain growth behavior and ferroelectric properties such as remanent polarization were different in these two kinds of film, the effects of La doping in the BLT thin film were very obvious.

Abstract: The cooling rate effect on the grain boundaries of the CaCu3Ti4¬O12 ceramic was investigated in this research. The resistance at the grain boundaries is found to be reduced as the cooling rate rises. The activation energies at the grain boundaries do not change with the cooling rate, suggesting that the conduction mechanism keeps the same in different cooling conditions. There is no significant difference in the permittivity of the samples. The dielectric loss can be lowered by using a smaller cooling rate. These results give clues to comprehend the conductive mechanism of the CCTO ceramic. The variation of the cooling rate may affect the re-oxidation process and cause the changes in electric properties.

Abstract: In this study, ferroelectric thin films of SrBi2Ta2O9 (SBT) or bilayered SrBi2Ta2O9/ Ba(Zr0.1Ti0.9)O3 (SBT/BZT) are successfully deposited on Si substrate under the optimal RF magnetron sputtering conditions, and their electrical and ferroelectric characteristics are discussed. Ferroelectric thin films are deposited on Si substrate under the RF power of 80 W, chamber pressure of 10 mTorr, substrate temperature of 550oC, and different oxygen concentrations. The surface morphology of deposited thin films is observed from the FESEM images, and the memory windows and leakage current of the Al/SBT/BZT/Si (MFS) structure are measured by an impendence phase analyzer and a semiconductor parameter analyzer, respectively. The memory window, capacitance and leakage current density of MFS structures under different oxygen concentrations are also reported. We find that the memory window of bilayered SBT/BZT structure shows larger than one of single layer SBT structure.

Abstract: Electric and dielectric properties of (1-x)Pb(Fe2/3W1/3)O3-xPbTiO3 solid solu¬tions were investigated as a function of the frequency and temperature. Dielectric measurements over the temperature showed the presence three contributions, which were related to the ferro-paraelectric phase transition (around 180K) and to conductive contributions (in the range 200K- 700 k). The FE phase transition of Pb(Fe2/3W1/3)O3 (PFW) is shifted to higher temperatures by PbTiO3 (PT) additions. Conductive contributions were associated to an electronic conductivity with activation energy around 0.45 – 0.55 eV.

Abstract: Nano-structured Barium Titanate (BaTiO3) was prepared by a hydrothermal method with the reaction between metatitanic acid and an alkaline solution of Ba(OH)2•8H2O. The morphology of as-obtained powders of BaTiO3 was determined by Scanning Electron Microscope, which revealed that well-dispersed nanoparticles were successfully synthesized. The phase composition was analyzed by X-ray diffraction, which shows that cubic phase of Barium Titanate was prepared. The optimal reaction conditions were discussed in detail.

Abstract: The present investigation reports on the preparation of BiFeO3 nanopowders by a sol-gel method using acetylacetone as a stabilizer. Single-phase BiFeO3 nanopowders without any impurity or amorphous phases were obtained when the precursor was thermal treated at temperatures as low as 400 oC for 2 h. Acetylacetone (acac) plays an important role on lowering the formation temperature of pure phase BiFeO3 nanopowders. It is found that Bi/acac molar ratio of 1/30 was favorable for a stable sol and for the lowest crystallization temperature of pure BiFeO3 nanopowders. X-ray diffraction and Fourier transform infrared spectroscopy revealed that thermally induced crystallization process of BiFeO3 nanopowders from Bi-Fe polymeric precursor. When the thermal treated temperature was below 200 oC, only amorphous phase existed. With the temperature increasing up to 300 oC, crystallized phase, carbonate, were detected. After annealed at 400 oC, Bi-Fe precursor totally changed to rhombohedral BiFeO3 nanopowders. Scanning electron microscopy characterized morphologies of BiFeO3 nanopowders calcined at 400 oC and 500 oC. The ferroelectric transition of BiFeO3 nanopowders at 827 oC has been detected by differential thermal analysis.

Abstract: High-quality bismuth modified zinc oxide ceramics were obtained by conventional ceramic method. The phase analysis revealed pure hexagonal ZnO phase in all the samples. High relative density (above 95%), when compared with theoretical density of ZnO, was achieved by the Arquimides’ method. Non-linear coefficients, obtained from the J-E curves, shown an increase in their values as the bismuth content increases. Complex impedance analysis revealed an increase of the semicircle diameters with the increase of the bismuth content. The obtained results will be discussed within the framework of the current theoretical model proposed in the literature.

Abstract: The optimized composition and sintering process of the low sintering X7R-type temperature-stable dielectric ceramics based on Barium Titanate in reducing atmosphere have been investigated. Flux aids SiO2-B2O3-Li2O were used in the experiments. The influence of composition and the content of flux agent on the microstructures and properties of ceramics materials were systemically studied. The X7R-type dielectric ceramics materials could be sintered at low temperature of 950oC in H2/N2 atmosphere, by optimizing flux content and adjusting process parameters. The dielectric constant of ceramics was effectively improved using two-step sintering process.

Abstract: In this paper, a method to synthesis barium titanate nanorods at room temperature and normal pressure by soft chemical is devoloped. Oleic acid is one important raw material in this method which will help to form reaction containers. The nanorods crystallized in the process. Samples were investigate by XRD, TEM and SAD and so on.

Abstract: BiFeO3-based single-phase multiferroics have been widely studied in both ceramics and films. However, the macroscopic magnetic properties of BiFeO3 ceramics were now most very weak. In this work, MnO2 and Co2O3 were used as B-site substitutes in BiFeO3 ceramics in order to the enhancement of magnetic properties. The change of magnetization was analyzed based on the phase composition and the microstructure of ceramics.