Papers by Author: Xi Yun He

Abstract: Highly transparent lead lanthanum zirconate titanate (Pb_1−xLa_x)(Zr_0.65Ti_0.35)_1-x/4O₃ (x=0.096-0.1) electro-optic ceramics were prepared by the hot pressing method. The ceramics exhibited transparency as high as 67% at 632.8nm (close to the theoretical value). The effects of lanthanum substitution on the phase structure, microstructure, dielectric, ferroelectric, optical and electro-optic properties of PLZT were examined systematically. The XRD results indicated that all the compositions were single perovskite phases, and La substitution decreased the lattice constant and unit-cell volume. The dielectric results showed that the T_max and ε_max decreased with La content increasing. The hysteresis loops showed that the La content reduced saturate polarization (Ps), remnant polarization (Pr) and coercive field (Ec). Moreover, the half-wave voltage and EO coefficient R was enhanced and reduced respectively with increasing La.

Abstract: Lead lanthanum zirconate titanate (PLZT) transparent ceramics have attracted more and more attentions for their unique electric-induced light scattering effects. The PLZT ceramics of 7.45 mole% lanthanum with different Zr/Ti ratios (Zr/Ti=68/32, 69/31, 70/30, 71/29, 72/28) were prepared by the hot-press sintering method. The X-ray diffraction patterns confirm that all the PLZT samples are perovskite structure without detected secondary phases. The SEM images of the fracture surfaces of the samples show that all the PLZT materials tend to fracture transgranularly, and exhibit fully dense and uniform microstructures. All the samples with different Zr/Ti ratios present typical relaxation ferroelectric phase transition characteristics with square shaped hysteresis loops. Noticeably, all the original PLZT samples show an excellent transparency in the wavelength range from visible to near-infrared, and they will become opaque after an appropriate electric field experienced. The opaque sample can also recover to the transparent state when an inverse compatible electric field acts on it. The contrast ratio of the sample increases firstly and then decreases when the Zr/Ti ratio increases from 68/32 to 72/28 (λ=632.8nm). The PLZT (7.45/70/30) material shows a maximum contrast ratio, which makes it promising to apply in optical modulators.

Abstract: La-modified 0.75Pb (Mg_1/3Nb_2/3)O₃-0.25PbTiO₃(PLMNT) electro-optic (EO) transparent ceramics were synthesized through a columbite precursor method. Excess PbO (10, 15 and 20 mol %) was added to study the effect on the transparency, electro-optic effect, and microstructures of PLMNT transparent ceramics. The phase structure of different samples can be identified as single perovskite structure with no second phase detected. The average grain size increased as the concentration of excess PbO increased from 10 mol% to 20 mol%. On the contrary, the transparency decreased with the increase of the concentration of excess PbO. When the concentration of excess PbO was 10 mol%, the transmittance was about 62% at 632.8nm. The EO coefficient was calculated through measuring the birefringence as a function of electric field. The EO coefficient increased with the increase of the concentration of excess PbO and the maximum EO coefficient reached 40.6×10^-16(m/V)² when the excess PbO was 20 mol%.

Abstract: Lead lanthanum zirconate titanate (PLZT) transparent ceramics present an attractive electrically controlled light scattering performance with high transmittance and large contrast ratio. PLZT ceramics of 8 mole% lanthanum with different Zr/Ti ratios (Zr/Ti=68/32, 70/30, 72/28) were prepared by the hot pressing method to figure out the influence of Zr/Ti ratios to the light scattering performance. X-ray diffraction patterns confirm that all the samples are perovskite structure with no secondary impurity phase detected. All the three compositions show double tending slim hysteresis loops which due to antiferroelectric phase coexisted. Besides, within the range of near-infrared to ultraviolet wavelength, all the PLZT samples show high transmittance. While the Zr/Ti ratio increasing from 68/32 to 72/28, the transmittance reduced value R_T of the sample decreases gradually (λ: 632.8 nm). PLZT (8/68/32) sample shows a maximum R_T, it promises a good application in optical modulators, goggles and so on.

Abstract: A series of Eu³⁺-substituted Mn _0.65 Zn _0.35 Fe _2-x Eu_xO₄ ( x = 0.00-0.04) nanoscaled ferrites were synthesized by a citrate sol-gel combustion processing. The effects of Eu ³⁺ substitution on the crystalline formation, microstructure and magnetic properties of Mn-Zn ferrite annealing at temperature from 500°C to 800°C were investigated. The results showed that the lattice parameter increased and it contributed to monophase spinel with the addition of Eu ³⁺ at x≤ 0.03. The remanence and coercive field increased with Eu ³⁺ substitution but it changed slightly in saturation magnetization when annealing ferrite powders at 700°C.

Abstract: A new process was developed for fabrication of multiferroic 1-3 type nanostructured composite films. In this process, eletrodeposition method was adopted to prepare the arrays of cobalt nanowires as ferromagnetic composition. The images, phase structure and magnetic properties were characterized by SEM, XRD and VSM, respectively. The results showed that applying magnetic field during electrodepostion process could improve the alignment and height uniformity of nanowires arrays, inducing (002)-orientation growth. The PZT (53/47) precursor solution prepared for ferroelectric composition was infiltrated the spaces between nanowires. After annealed at 700 °C for 20 min, the 1-3 type multiferroic composite film was achieved. Preliminary results show this technique to have the potential to become a practical fabrication process for 1-3 type multiferroic composite films.

Abstract: Ba0.6Sr0.4TiO3 materials doped with boron family Al3+, Ga3+ and In3+ are prepared by a ceramic process. The specimens possess condense microstructures. A low dielectric loss is achieved in the sample doped with In3+. Dielectric constants increase with decrease of the radii of doped ions. The results are discussed with respect to the interaction between oxygen ions and ions at B-site in ABO3 perovskite, which is revealed by Fourier transform infrared spectrum.

Abstract: Bi3.5Nd0.5Ti3O12 (BNT) ferroelectrics modified with different concentrations of Nb are prepared by a hot-pressing method. XRD diffraction shows that all samples have only a layeredstructured pervoskite phase. Raman spectra confirm that the crystal symmetry change locally when increasing Nb concentration. It is found that the introduction of a suitable amount of Nb can enhance the remnant polarization of BNT. The temperature dependence of dielectric constant is also investigated in BNT ceramics. All samples have high Curie temperature above 530°C.

Abstract: PLZT (9/65/35) thin films on sapphire (001) substrates with thickness of 0.1 ~ 0.9 µm were prepared by a metal-organic decomposition (MOD) process. All the films present highly (110)-preferred orientation independent of the film thickness. The microstructure of the films was investigated. The influence of film thickness on optical properties of PLZT films was examined and analyzed. As the film thickness is increased, the absorption edge of the film is shifted to longer wavelength; the optical band gap Eg is increased slightly. The refractive index at 510nm determined from optical transmission spectra also shows an increasing tendency as film thickness increasing. Great stress aggregated during the film preparing process is thought to be an important reason which results in the variations of optical properties of the films with different thickness.

Abstract: Polycrystalline dysprosium (Dy) doped PLZT ceramics with compositional formula [Pb0.88 (La1-xDyx)0.12](Zr0.40 Ti0.60)O3] were prepared by hot-pressed solid-state method. Dy3+ concentration x varied from 0 to 0.5. All samples present single phase with tetragonal structure and the tetragonality was increased with increasing Dy3+ content. The Raman spectra indicated that Dy3+ ions could be distributed in both A and B site of ABO3 perovskite structure depending on the doping amounts.