Papers by Keyword: Ferroelectric

Abstract: Synthesis of Zn-doped PbTiO3 was done using solid-state method. The effects of varying amount of Zn were investigated. Stoichiometric amount of precursors were mixed and ground. The pressed mixtures were calcined at 800°C and sintered at 1,100 °C after regrinding. The samples were characterized using X-ray Diffraction (XRD), Differential Thermal Analysis (DTA), and Scanning Electron Microscopy (SEM). The XRD verifies the existence of PTO in the samples. DTA shows the thermal profile of the samples. Among the different concentrations of Zn that were added, the sample with 5% mole fraction showed the lowest melting point. For 5% mole fraction and greater, SEM images showed flattening and fusing of grains.

Abstract: In the present study, the BaTiO3/Ni composites were prepared by using the pressureless sintering technique. The ferroelectric and ferromagnetic properties of the composites are measured. The composites exhibit ferroelectric properties only when the Ni content is as low as 1 vol.%. Nevertheless, the saturated magnetization of the BaTiO3/Ni composites increases with the increase of Ni content. The BaTiO3/Ni composites exhibit multiferroic characteristics.

Abstract: Bi4Ti3O12 based thick films were prepared by screen printing and firing using Pt bottom electrodes and ZrO2 substrates. The influence of excess Bi2O3 as sintering aid was investigated. Furthermore, substitution of Ti-site and Bi-site for V5+ and Nd3+ was performed. Screen-printable pastes were prepared by kneading the Bi4Ti3O12 based powder and Bi2O3 powder in a three-roll mill with an organic vehicle. The microstructures and ferroelectric properties of the thick films were examined in comparison with bulk ceramics. The remanent polarization of 9.6 μC/cm2 and coercive field of 64 kV/cm were obtained for the Bi3.0Nd1.0Ti2.99V0.01O12 thick film with 10 wt% of excess Bi2O3 fired at 1200OC.

Abstract: Single crystals of K0.47Na0.53NbO3 (KNN) and Mn-substituted KNN (Mn-KNN, K0.53Na0.47Mn0.004Nb0.996Oy) were grown by a flux method, and the influence of lattice defects on the polarization and leakage current properties was investigated. As-grown KNN did not show an apparent polarization hysteresis loop due to its large leakage current (~10-3 A/cm2). The substitution of 0.4%-Mn at the Nb site and subsequent annealing under a moderate oxidative condition were effective in suppressing the leakage current of KNN crystals. 0.4%-Mn-KNN annealed at 1100°C in air exhibited a low leakage current (~10-8 A/cm2), a relatively large remanent polarization of 40 μC/cm2 and a coercive field of 12 kV/cm at 25°C. The oxidation of Mn and Nb ions during annealing in air is found to play an essential role in the low leakage current of Mn-KNN.

Abstract: The microstructure and ferroelectric domains of SrBi2Ta1.6Nb0.4O9 ceramics were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) equipped with energy dispersive spectroscopy (EDS). The X-ray diffraction patterns show that the lattice constants a and b decrease, and c increases by doping with Nb into SBT sample. Accordingly, it has large strain and lattice distortion in the lattice This suggests that the Nb atoms partially occupy the location of the Ta atoms in the lattice. From TEM observations, the grains show (008) preferred orientations in the sample, which agrees well with the XRD results. The 90° domain walls are identified by the 90° rotation relationship of the electron diffraction pattern about the [001] zone axis. The 180° domain walls and anti-phase boundaries (APBs) in Nb-doped SBT ceramics are also observed, which are irregularly shaped and highly curved. The traditional α-fringes can be found in the Nb-doped SBT ceramics, which are the evidence of large strains in the lattice.

Abstract: Ferroelectric Pb(Zr0.6Ti0.4)O3 (PZT(60/40)) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The Pt bottom electrodes were screen-printed on the alumina substrate. The PZT(60/40) thick films were annealed at 1050°C for 10min in PbO atmosphere. Pb(Zr0.4Ti0.6)O3 (PZT(40/60)) precursor solution, which prepared by sol-gel method, was spin-coated on the PZT thick films to obtain a densification. These PZT multilayered thick films were annealed at 650°C for 2 h in PbO atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at 590°C for 10min. Its structural and electrical properties of the PZT thick films with the treatment of PZT(40/60) precursor solution coating were investigated. The coating and drying procedure was repeated 4 times. And then the PZT(40/60) precursor solution was spin-coated on the multilayered thick films. A concentration of a coating solution was 1.5 mol/L and the number of coating was repeated from 0~15. The porosity of the thick films was decreased with increasing the number of coatings. All PZT multilayered thick films showed the XRD patterns of typical peroveskite polycrystalline structure. The relative dielectric constant of the PZT-15 (15: number of solution coatings) thick film were 370. And the PZT-15 thick film shows the remanent polarization of 23.5 μC/cm2 and coercive field of 18.0 kV/cm, respectively.

Abstract: Ferroelectric PZT(70/30) thick films were fabricated by the hybrid technique adding the sol coating process to the screen-printing process to obtain a good densification. Structural and electrical properties of the thick films with the sol concentration were investigated. The relative dielectric constant increased and dielectric loss decreased with increasing the sol concentration, the values of the thick film coated with sol concentration of 1.5 M were 698 and 2.5 % at 1 kHz, respectively. And the remanent polarization and dielectric breakdown strength of the thick film coated with sol concentration of 1.5 M were about 38 μC/cm2 and 200 kV/cm, respectively. The leakage current densities were less than 10-8 A/cm2 at the applied electric field range of 0-100 kV/cm in all thick films.

Abstract: Propagation and deflection of microcracks driven by electric loading in <001>-oriented 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 ferroelectric single crystals were investigated using an in-situ transmission electron microcopy (TEM) technique. The static observation of the domain pattern revealed the coexistence of sub-micrometer and nano-meter domains. Electric field induced deviation from the main microcrack path and subsequent propagation along the direction almost perpendicular to the electric field were observed directly. A qualitative analyses is given based on the maximum energy release rate criterion.

Abstract: Bipolar electric fatigue in ferroelectric niobium-doped lead zirconate titanate stannate ceramics was investigated. Variations in the polarization and strain hysteresis loops as well as microstructural modifications of the material due to the electric cycling were analyzed. Compared with ferroelectric PZT ceramics cycled under similar conditions, the material exhibited a higher resistance to electric fatigue. Properties of the specimens showed significant decays above 106.5 cycles. Asymmetric suppression of strain hysteresis loop was monitored. At 108 cycles, the remanent polarization, the right maximum strain and the left maximum strain decreased to 70%, 58% and 44% of their initial values, respectively. The color of the material was changed from pale yellow to dark grey with cycling. The properties and color of the fatigued samples were recovered almost fully to those of the virgin state after a heat treatment at 500oC for 1 h. The pinning of domain walls, probably by oxygen vacancies, was concluded to be the predominant fatigue mechanism for the material.