Lanthanum-modified Lead Zirconate Titanate Ceramics Research Articles

A novel vacuum/oxygen hot press sintering approach for the fabrication of transparent PLZT (7.4/70/30) ceramics

Transparent Lanthanum-modified lead zirconate titanate ceramics (PLZT 7.4/70/30) with low content of excess lead oxide (PbO) were successfully prepared by a novel vacuum/oxygen hot press sintering process. The phase structure, microstructure, electrical properties and electro-optic scattering performance of PLZT ceramics as a function of excess PbO in the starting powders have been studied and analyzed. As a result, these ceramics exhibited an ultra-high optical transmittance (>69.4% at 1064 nm; thickness 1 mm) from visible to near-infrared wavelength. Herein, we significantly reduce the use of PbO as an auxiliary agent for sintering. This puts forward a good route to meet the objectives of environmental protection and sustainable development.

Electrocaloric response in lanthanum-modified lead zirconate titanate ceramics

Recent findings of a large electrocaloric (EC) effect in polymeric and inorganic ferroelectric materials open a potential possibility of development of solid-state cooling or heating devices of new generation with better energy efficiency that may be less harmful for the environment. We investigate by using direct measurements, the temperature and electric field dependence of the electrocaloric response in Pb1-xLax(ZryTi1-y)1-x/4O3 bulk ceramics (PLZT) with x = 0.06 and 0.12. Here, the properties of the EC response were probed in a part of the PLZT composition phase diagram with low y = 0.40 composition, in which the EC effect was not previously studied. Measurement results show the existence of the sizeable EC response in the 12/40/60 PLZT sample with the EC temperature change (ΔTEC) of 2.92 K at 430 K and 80 kV/cm. This value exceeds previously obtained ΔTEC values in relaxor ferroelectric x/65/35 PLZT compositions, rivaling the best EC response in lead magnesium niobate-lead titanate ceramics. The electrocaloric responsivity (ΔT/ΔE) value of 0.41 × 10−6 Km/V determined at a lower electric field of 20 kV/cm and 410 K is comparable to those observed in other perovskite ferroelectrics.

Photostriction properties of PLZT (4/52/48) ceramics sintered by SPS

In this paper, the preparation and sintering process of Lanthanum-modified lead zirconate titanate ceramics (PLZT 4/52/48) powders and ceramics were investigated. The PLZT powders were prepared by co-precipitation and sol-gel methods. It is confirmed that PLZT powders synthesized by sol-gel method had smaller grains and better dispersion. The atmosphere sintering and spark plasma sintering（SPS）technique were used to sinter the PLZT ceramics separately. After sintering, the physical, electrical, and optical properties of the PLZT ceramics sintered by different methods were tested. The results show that the SPS sintering can increase the densification degree (reaching 99.5%)of the PLZT ceramics, which improved the transparency, ferroelectric, piezoelectric and optical properties of PLZT ceramics. It is found that when the light intensity reached 600 mW/cm2, the maximum photo-induced strain of the SPS sintered ceramic was as high as 10. 84 × 10−3, which was almost 1.4 times larger than that of the atmosphere-sintered sample. Obviously, the sol-gel method and SPS process can enhance the comprehensive performance of PLZT ceramics.

Optical amplification in disordered electrooptic Tm3+ and Ho3+ codoped lanthanum-modified lead zirconate titanate ceramics and study of spectroscopy and communication between cations

Rare earth doped electro-optic (EO) ceramics of lanthanum-modified lead zirconate titanate (PLZT) are promising in building multifunctional optical devices, by taking advantage of both EO effect and optical activity. In this work, the combination of the measured spectra of absorption and photoluminescence, the fluorescent decay, the calculated Judd-Ofelt parameters, and measured single pass gain in Tm3+, Ho3+ codoped PLZT ceramics have marked them out as promising gain media in building electrically controllable lasers/optical amplifiers and other multifunctional devices. Optical energy storage was also observed in the optical amplification dynamics.

The temperature dependences of electromechanical properties of PLZT ceramics

The mechanical and electrical properties in lanthanum modified lead zirconate-titanate ceramics of 5/50/50 and 10/50/50 were studied by mechanical loss Q - 1, Young's modulus E, electric permittivity e and tangent of dielectric loss of angle tgδ measurements. The internal friction Q - 1 and Young modulus E measured from 290 K to 600 K shows that Curie temperature TC is located at 574 K and 435 K (1st cycle of heating) respectively for ceramic samples 5/50/50 and 10/50/50. The movement of TC in second cycle of heating to lower temperature (561 K for 5/50/50 and 420 K for 10/50/50) has been observed. Together with Q - 1 and E measurements, temperature dependences of e=f(T) and tgδ=f(T) were determinated in temperature range from 300 K to 730 K. The values of TC obtained during e and tgδ measurements were respectively: 560 K for 5/50/50 and 419 K for 10/50/50. These temperatures are almost as high as the temperatures obtained by internal friction Q - 1 measurements in second cycle of heating. In ceramic sample 10/50/50 the additional maximum on internal friction Q - 1 curve at the temperature 316 K was observed.

Determination of the quasistatic linear and non-linear dielectric response in relaxor materials

Temperature dependence of the first ε 1 and third harmonic dielectric response ε 3 in relaxor systems was studied both as a function of the dc electric field by utilising the charge accumulation technique and as a function of the ac electric field. Additional non-linear contribution was found in the ac field dependence of ε 1 in lead magnesium niobate single crystals and in lanthanum-modified lead zirconate titanate ceramics. This dominating contribution in the field dependence of ε 1( ω) has an origin in the fact that the increasing field shifts the relaxor state from the glassy to a particular crossover state in the glassy-to-ferroelectric crossover region. This was confirmed by quasistatic measurements of the total third-order non-linear dielectric response ε 3 t as a function of the dc electric field throughout the glassy-to-ferroelectric crossover region. It is shown that the total third-order non-linear dielectric response can be understood within the extended spherical random bond-random field model of relaxor ferroelectrics.

Photostrictive effect in lanthanum-modified lead zirconate titanate ceramics near the morphotropic phase boundary

Photostrictive effect in lanthanum-modified lead zirconate titanate (PLZT) ceramics, one of the promising candidates for photostrictive materials, has been investigated with different contents of La and the ratio of Zr/Ti near the morphotropic phase boundary compositions. The maximum photocurrent and photovoltage were obtained at different compositions of PLZT ceramics: maximum photocurrent at 4/48/52, maximum photovoltage at 5/54/46. New figures of merit for evaluating these materials, which includes both the magnitude of strain and response speed, were proposed.

Electric-field–temperature phase diagram of the relaxor ferroelectric lanthanum-modified lead zirconate titanate

Transition lines between various phases in the electric-field--temperature phase diagram of 9/65/35 lanthanum-modified lead zirconate titanate ceramics were determined by measurements of the temperature and electric-field-dependent dielectric constant. Above a critical field ${(E}_{C})$ the dc bias electric field induces a transition from the relaxor (R) to the long-range ferroelectric (FE) phase. In the temperature direction of the approach to the FE phase the R-FE transition line was determined from the field-cooled--field-heated dielectric susceptibilities, while depolarization temperatures were obtained from the field-cooled--zero-field-heated dielectric susceptibilities. A considerably large shift was found for the above two R-FE transition lines demonstrating the strong impact of the electric field on the stability of the FE phase with increasing temperature. It was found that below ${E}_{C}$ ergodicity is broken due to the divergence of the longest relaxation time at the freezing temperature ${T}_{0}=259 \mathrm{K}.$ Hence the system exhibits a transition line between the ergodic (ER) and nonergodic (NR) relaxor state. In the dc bias field direction of the approach to the FE phase, the temperature dependence of ${E}_{C},$ i.e., the transition lines between ER or NR and FE phases were studied by measurements of the complex dielectric constant as a function of a dc bias field at several fixed temperatures. The experimental results are compared with the results of a spherical random bond-random field model of relaxor ferroelectrics.

Influence of Composition and Dopant on Photostriction in Lanthanum-Modified Lead Zirconate Titanate Ceramics

The anomalous photovoltaic effect, i.e., substantial voltage generation exceeding band gap energies, by homogeneous illumination in the non-centrosymmetric materials is a wellknown phenomenon. This mechanism is fundamentally different from those observed in heterojunctions/homojunctions (i.e., solar cells) based on semiconductor materials with a symmetric crystal structure. Recently, light induced strain termed as Photostriction, has been demonstrated in noncentrosymmetric perovskite ferroelectrics as lanthanum-modified lead zirconate titanate (PLZT) ceramics. PLZT ceramics have gained considerable attention due to their large photostrictive responses. When a light is illuminated on a polarized photostrictive bimorph, a large photovoltage of the order of kV/mm is generated across its length in the spontaneous polarization direction which results in strain generation by converse-piezoelectric effect and caused the bimorph to deflect in the direction away from the illumination. The photoactuation has been demonstrated in PLZT ceramic wafers as two different kinds of actuators, (i) photo-driven relay and (ii) photo-driven micro walking machine. These materials are also promising for the photo-acoustic device (e.g., Photophone) of the optical communication system. However, photostriction being a recently observed phenomenon, is far from optimum condition. It is expected that the optimization with respect to materials and microstructural characteristics will lead to a substantial enhancement in the photoactuation efficiency. Increasing the photoactuation efficiency will eliminate the need for electrical energy, and will open up numerous possibilities of contactless actuators. In this paper the influence of composition dependence and impurity doping effects on microstructure and photostrictive responses of PLZT ceramics have been investigated.

Raman spectroscopy investigation of the phase transition sequence in lanthanum-modified high zirconium -content lead zirconate titanate ceramics

Abstract The phase-transition sequence in lanthanum-modified lead zirconate titanate ceramics with between 0 and 4 at.% lanthanum and a Zr/Ti ratio of 92/8, (PLZT 100×/92/8), has been investigated using Raman spectroscopy and dielectric measurements. An antiferroelectric (AFE)-two ferroelectric (FR(LT)) and (FR(HT)) and paraelectric (Pc) phase sequence was confirmed for x 1%, the coexistence of antiferroelectric (AFE) and ferroelectric (FR(HT)) phases has been observed in the Raman spectra of these ceramics near 200 K.

Effects of lanthanum modification on rhombohedral Pb(Zr1−xTix)O3 ceramics: Part II. Relaxor behavior versus enhanced antiferroelectric stability

Lanthanum-modified lead zirconate titanate ceramics Pb1−3/2xLax(Zr1−yTiy)O3 [PLZT 100x/100(1 − y)/100y] with Zr/Ti ratios close to the antiferroelectric-ferroelectric (AFE-FE) phase boundary were investigated by dielectric spectroscopy, Sawyer–Tower polarization techniques, and electron microscopy. An incommensurate antiferroelectric (AFEIn) phase was found to be stabilized from the rhombohedral FE state in the compositional series 100x/90/10 for x ≥ 0.02. The La content required to induce the AFEIn state increased as the Ti content was increased. For 100x/85/15, a state with relaxor-like dielectric behavior and nanodomains was observed to develop with increasing La content; however, the double-loop-like P-E curves were suggestive of antiferroelectric behavior. Investigations for the composition 6/85/15 revealed the formation of nanodomains from the AFEIn modulation, where the size of the nanodomains equaled the value of the AFEIn modulation wavelength. For this composition, P-E studies revealed double hysteresis characteristics, whereas dielectric investigations revealed relaxor-like behavior. It is suggested that the order within the nanodomain state may be antipolar over a range of compositions in high La content rhombohedral PLZT ceramics.