Bin Xia

Electrically induced light scattering performances of lanthanum-modified lead zirconate titanate transparent ceramics

A series of lanthanum-modified lead zirconate titanate (PLZT) ceramics of Zr/Ti (70/30) with different La concentration (Lau2009=u20097.6, 7.8, 8.0 mole %) were prepared by a hot pressing process. The performances of electrically induced light scattering for PLZT (X/70/30) ceramics were investigated and analyzed systematically. All samples are crystallized into a single perovskite phase. The PLZT (7.6/70/30) sample exhibits a ferroelectric behavior while both PLZT (7.8/70/30) and PLZT (8.0/70/30) samples show an antiferroelectric behavior. The phase transition temperature (Tc) of the PLZT (X/70/30) ceramics shifts slightly from ~86xa0°C to ~89xa0°C with the increasing of La concentration at 1xa0kHz. All three ceramic samples exhibit a high transmittance, i.e., greater than 60xa0%, with a thickness of 0.4xa0mm over a wide range of wavelength band, from visible to near IR. The PLZT (X/70/30) ceramics exhibit three different types of light scattering behavior depending on the La concentration (examined at λu2009=u2009632.8xa0nm). Among them, PLZT (8.0/70/30) presents a unique applicable auto-switchable property with a low threshold value of electric field and high transmittance. Noticeably, the contrast ratio increases correspondingly with the thickness of the sample, and the contrast ratio aroused by the transverse electric field is about twice as big as that aroused by the longitudinal one. The light scattering properties of the PLZT (8.0/70/30) ceramic may represent a creative application in optical modulators.

Effect of anisotropy on the ferroelectric, optical, and electro-optic properties of PLZT transparent ceramics prepared by uniaxial hot-press sintering techniques

PLZT (X/70/30) ceramics with different La contents (X = 7.45, 7.51,7.57, 7.63) were fabricated to study the effect of anisotropy on ferroelectric, optical, and electro-optic properties in parallel and normal to the uniaxial hot-press sintering direction (abbreviated as parallel and normal), respectively. All samples show the square hysteresis loops but the tetragonality with ferroelectricity is more evident in a parallel direction than that in normal direction. The high transmittances (≥60%, 0.35mm, visible to near infrared light) are obtained. However, the transmittances and the light scattering contrast ratios are higher in the normal direction. The PLZT (7.63/70/30) ceramic exhibits the more stable electrically controlled light scattering behavior in parallel direction and its contrast ratio reaches to the maximum 1.37 in a normal direction in this system.

Light Scattering Properties for PLZT Transparent Ceramics of Different Zr/Ti Ratios

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 RT of the sample decreases gradually (λ: 632.8 nm). PLZT (8/68/32) sample shows a maximum RT, it promises a good application in optical modulators, goggles and so on.

A Comparative Research on PLMNT Relaxor Ferroelectric Ceramic Prepared by Conventional and Hot-Press Techniques

PLMNT3/75/25 ceramics were prepared by uniaxial hot-press sintering method and conventional sintering method, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer were used to measure the properties of the PLMNT ceramics. PLMNT ceramic with pure perovskite phase was fabricated by uniaxial hot-press sintering method, while, a secondary pyrochlore phase was found in PLMNT ceramic prepared by conventional sintering method. It was observed that the PLMNT ceramic fabricated by uniaxial hot-press sintering showed better densification and more uniform grain size than that of the PLMNT ceramic prepared by conventional sintering. The dielectric responses showed that the samples prepared by two methods both exhibited diffuse phase transition characteristic, and the values of the diffusivity parameter were calculated according to the linear fitting of the modified Curie-Weiss law. The relaxor ferroelectric characteristics of PLMNT ceramics accorded well with the Vogel-Fulcher relationship. The P-E hysteresis loops of the samples from uniaxial hot-press sintering were apparently slight than that of conventional sintering samples, while the value of the Ps (saturation polarization) was significantly higher.

Lanthanum Dependence of the Electrically Controlled Light Scattering Performances of PLZT Transparent Ceramics

Lead lanthanum zirconate titanate (PLZT) transparent ceramics have attracted more and more attentions for their unique electrically controlled light scattering effects. By the hot-press sintering method, a series of PLZT (X/70/30) ceramics with different La concentration (7.3, 7.4, 7.45, 7.5, 7.6 mole %) have been synthesized to figure out its influence on the electrically controlled light scattering performances. XRD patterns reveal the formation of a single-phase perovskite structure for all samples. The PLZT (7.3/70/30, 7.4/70/30, 7.45/70/30) samples exhibit a ferroelectric behavior, but with the La concentration increasing, the samples exhibit a tendency of a double hysteresis loop which is due to antiferroelectric phase coexisted. The temperature of maximum dielectric constant (Tm) of the PLZT (X/70/30) ceramics shifts from ~99 °C to ~87 °C with the increasing of La concentration at 1 kHz. All samples exhibit a high transmittance (61%, 0.35 mm) within the wavelength range from visible to near-infrared light. Depending on the La concentration, the light scattering behavior of PLZT ceramics exhibit two main types, in which PLZT (7.45/70/30) promises a unique potential application in laser modulators for its outstanding advantages of less energy consumption and relatively larger contrast ratio.

Effects of La Doping on Microstructure and Ferroelectric Properties of BLTN Lead-Free Ceramics

Lead-free EO ceramics have been received increasing attentions from the view point of green environment in recent years. In this study, lead-free Ba6-1.5xLaxTi2Nb8O30 (0≤x≤7%) ceramics were synthesized by the conventional solid state reaction sintering method. The effects of lanthanum doping on the microstructure and electrical properties of Ba6Ti2Nb8O30 (BTN) ceramics were investigated and analyzed. The XRD results revealed that the lanthanum doping changed the BTN lattice parameters slightly. The sample grain size, dielectric constants (1kHz) and the temperature Tm gradually decreased with the increasing of lanthanum doped content. The optimized BLTN ceramic sample with x=4 mol % exhibited a good transparency and excellent electrical properties (Ps=6.41 μC/cm2, Pr=0.77 μC/cm2, and Ec=3.80 kV/cm).

Effects of Annealing on Properties of PLZT (8/68/32) Electrically Controlled Light Scattering Ceramics

PLZT (8/68/32) electrically controlled light scattering ceramics with fully dense microstructure and high transmittance were prepared by a hot-press sintering method. The effects of annealing on dielectric, ferroelectric, optical and electrically controlled light scattering properties were examined and analysed. The XRD patterns indicated that all sintered specimens were well crystallized and the peak of 2θ∼30.8° gradually shifted to high degree. The temperature dielectric spectrum manifested the obvious relax or phase transition. And the double-look-like ferroelectric hysteresis loops revealed the tendency to transform a slim loop with the significant reduction in remnant polarization and coercive field via annealing treatment. Then the transmittance (from 58 to 62%, E = 0, λ = 632.8 nm) and contrast ratio (from 545:1 to 699:1) clearly increased after annealing treatment. The light scattering behavior of the PLZT samples was improved obviously.

Evidence of Normal to Anti Ferroelectric Phase Transition of PLZT Transparent Ceramics of Different Zr/Ti Ratio

The lanthanum-modified lead zirconate titanate transparent ceramics with different Zr/Ti ratio were prepared by the hot pressing sintering method. A single perovskive structure with a dense microsctructure was obtained and the transgranular fracture of PLZT ceramics tended to be more serious As the Zr/Ti ratio increases, the transmittance of PLZT ceramics tended to be higher and the transgranular fracture became more serious. The P-E loops changed froe a square hysteresis loop to a double tending slim hysteresis loop. Besides,the S-E loops changed from a approximate parabolic shape to a butterfly shape. These two loops confirm the transition from normal ferroelectric to anti ferroelectric phase occured with the Zr/Ti ratio increasing.

Effects of Sintering Atmosphere on the PLMNT Transparent Ceramics Prepared by Hot-Press Sintering Method

La modified Pb(Mg1/3Nb2/3)O3-PbTiO3 (PLMNT) transparent electro-optic (EO) ceramics with pure perovskite phase were fabricated by the uniaxial hot-press sintering method. An improved hot-press sintering technique with varied atmosphere was proposed to eliminate the pore defects. It consists of four stages: 1) sintering at a relatively low temperature (800°C) in the vacuum atmosphere first, and then in the pure O2 atmosphere; 2) sintering in a pure O2 atmosphere at high temperature by uniaxial hot-press method; 3) replacing the O2 atmosphere with CO2 gas to eliminate the residual closed pores; 4) finally exchanging CO2 atmosphere with pure O2 gas to eliminate the oxygen vacancies. The research results certified that the thermal treatment in the vacuum atmosphere and CO2 atmosphere could eliminate the residual closed pores and improve the transmittance of the PLMNT transparent ceramics effectively. By the improved hot-press sintering technique, the optical transmittance of the polished PLMNT transparent ceramics with a thickness of 0.35mm increases from 61% to 64% at 632.8nm. The reasonable explanation was given about the mechanism of the improvements of this sintering technique.

Effects of Zr/Ti Ratio on the Electric-Induced Light Scattering Performances of PLZT Transparent Ceramics

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.