Influence of low external magnetic field on electric field induced strain behavior of 9/70/30, 9/65/35 and 9/60/40 PLZT ceramics

In this work, Pb_0.91La_0.09(Zr_xTi_1−x)_0.9775O₃ PLZT ceramics, where x =0.70, 0.65 and 0.60, were prepared by a solid-state mixed-oxide technique. Structural information was investigated by X-ray diffraction method. Electric field induced polarization and strain behavior of the PLZT ceramics under an influence of static magnetic field were measured by a Sawyer-Tower circuit in conjunction with Michelson interferometer at various static magnetic fields (0–30.7 mT). The results showed that the imposed magnetic field affected the polarization and induced strain behaviors in PLZT ceramics More interestingly, the imposed magnetic field showed more significant influence on the PLZT ceramic composition near morphotropic phase boundary (MPB), i.e. PLZT 9/65/35. The spontaneous polarization of 180° domain switching was seen to be suppressed by the applied magnetic field.     

Study of aging behavior of 9/70/30 and 9/65/35 PLZT by optical interferometric technique

In this work Pb_0.91La_0.09(Zr_0.70Ti_0.30)_0.9775O₃ PLZT (9/70/30) and Pb_0.91La_0.09(Zr_0.65Ti_0.35)_0.9775O₃ PLZT (9/65/35) ceramics were prepared at four different sintering temperatures by solid solution method. The samples were aged by keeping at room temperature for 19 days. After the aging process, structural and electrical properties of the samples were studied using Modified Michelson Interferometer, LCR meter and X-ray diffraction. The effect of the Zr/Ti ratios on the dielectric and ferroelectric properties was also investigated. The aged PLZT (9/70/30) showed pinched P–E loop and remnant strain in rhombohedral phase, while PLZT (9/65/35) showed distort s–E shape implying non-180° domain in tetragonal phase.     

A Novel Mechanism for Relaxor–Ferroelectric Transition in PLZT(8/65/35)

We report a novel mechanism for the spontaneous transition to the ferroelectric (FE) phase in a typical relaxor, PLZT(8/65/35). Dielectric, FE, induced strain, and structural studies reveal the influence of acceptor dopant Cu²⁺ on this transition. That this transition occurs under zero-field conditions reveals yet another challenge in the use of copper metal electrodes for PLZT-based thin-film devices.     

Electrical creep around a circular hole in PLZT 8/65/35

The strain-birefringence correlation was exploited to study the local behaviour near a circular hole in unpoled PLZT 8/65/35 under electric field below than the coercive field. The observed birefringence contours near the hole show a spatial distribution and time dependence. Due to the enhancement of electric field near the hole, the polarization creep rate is greatly increased. The evolution of the local principal strain difference with time and position in the sample is quantified. Overall, an accelerated poling effect is found in comparison with the behaviour under uniform field. This appears to be due to inhomogeneous field distribution which initiates polarization switching in areas of locally enhanced electric field. The presence of the hole promotes a nearly linear growth in average polarization with time, despite the strongly nonlinear response of the parent material. The results indicate that insulating porosity can strongly affect the switching behaviour and coercivity of ferroelectric ceramics.     

Dielectric,ferroelectric and induced strain behavior of PLZT 9/65/35 ceramics modified by Bi2O3 and CuO co-doping

PLZT 9/65/35 (Pb_0.91La_0.09(Zr_0.65Ti_0.35)_0.9775O₃) ceramics with addition of 0.25, 0.5 and 1.0 wt% of Bi₂O₃/CuO (where the ratio of Bi₂O₃:CuO=9:1 by mole) were prepared by sintering at the temperatures between 1000 and 1200 °C. It was found that Bi₂O₃/CuO could bring the sintering temperature down ~50 °C to obtain PLZT with no second phase. Dielectric and ferroelectric properties were investigated. Bi₂O₃/CuO decreased both coercive field and remnant polarization, which was caused by an increase of the degree of diffuseness in relaxor ferroelectric materials. Electric field induced strain behavior was also investigated and it was found that the addition of Bi₂O₃/CuO increased the maximum induced strain and maximized electrostrictive effect. Therefore, Bi₂O₃/CuO was useful as a sintering aid, which improved the dielectric and the relaxor ferroelectric properties as well as the electric field induced strain of PLZT ceramics.     

Effects of Preparation Conditions on the Structural and Optical Properties of Spark Plasma-Sintered PLZT (8/65/35) Ceramics

Transparent lanthanum-doped lead zirconate titanate (PLZT) ceramics with high density were fabricated using spark plasma sintering (SPS), a recently developed hot-pressing method. A wet–dry combination method was used to prepare the fine PLZT powders. The average grain size of the PLZT ceramics was less than 1 μm, because of a relatively low sintering temperature and a very short sintering time. The transmittance of PLZT ceramics increased with an increase of calcination temperature up to 700°C and then it slightly decreased with further increase of calcination temperature. The transmittance strongly depended on the SPS temperature and heat-treatment temperature. The pellet sintered at 900°C for 10 min and heat treated at 800°C for 1 h with a thickness of 0.5 mm showed a transmittance of 31% at a wavelength of 700 nm. The relationships between the transmittance and the microstructure were investigated.     

Electron emission from Pb0.88La0.08(Zr0.65Ti0.35)O3 ferroelectric ceramics

The electron emission characteristics of PLZT 8/65/35 ferroelectric are studied. High current density has been obtained from PLZT 8/65/35 ferroelectric cathode. The source of the disturbance in the experiment is discussed and several methods to reduce the disturbance are proposed. It is discovered that there is a voltage threshold, and the electron emission will not occur until the amplitude of the pulse exceeds the threshold. Moreover, there are two current peaks in the FE electron emission curves, the primary peak remains stable in location and intensity, while the secondary one shows instability during repeating experiments.     

Chemical preparation of PLZT powders by the carbonate method

PLZT powders were prepared by the adsorption-type coprecipitation method, in which mixed ammonium carbonate and ammonium hydroxide aqueous solution was used as a precipitant. The resulting precipitates are mixtures of carbonates and hydroxides. After calcining at 600°C a powder was obtained, consisting of two phases of the zirconium-rich and the titanium-rich perovskite structures with lattice parameters of about 4·13 Å and 3·99 Å, respectively. As calcination temperature increased, these two phases tended to dissolve each other gradually, and then a single perovskite structure appeared as the temperature rose above 900°C. By the results of X-ray diffraction, SEM, TEM and DTA/TGA, the behavior of coprecipitated powders and calcining treatments have been discussed. The atmosphere sintering technique was used to examine the sinterability of the PLZT powders, and a transparent PLZT ceramic was thus obtained.     

Lanthanum Dependence of Elastic and Piezoelectric Properties of PLZT Ceramics with a Zr/Ti Ratio of 65/35

The elastic and piezoelectric properties of PLZT ceramics with a 65/35 Zr/Ti ratio undergo pronounced changes as La is added to the structure. At the rhombohedral-tetragonal phase boundary, material constants plotted as functions of La concentration show strong discontinuities in slope; these discontinuities provide a precise means of locating the boundary. The radial-mode coupling factor, k_p , compliance coefficient, S₁₁ ^E , and piezoelectric coefficient, d₃₁ , attain peak values at the boundary, whereas Poisson's ratio, σ^E, and the resonance-frequency constant exhibit pronounced minima. This behavior is evidence of the increasing ferroelastic sensitivity of the material as the distortion angle of the rhombohedral phase approaches a minimum.     

Gas and water vapour transport in a polyketone terpolymer

Gas and water vapour transport properties of a polyketone terpolymer (0.93/0.07/1 ethylene/propylene/carbon monoxide) have been investigated and related to the polymer structure. Permeability tests have been performed at several temperatures (from 25 to about 65°C) with five different gases (oxygen, nitrogen, methane, ethane and carbon dioxide), evaluating permeabilities, diffusivities and solubilities. Their dependence on temperature was interpreted on the basis of apparent activation energies of permeation and diffusion (E_P and E_D) and of heats of solution (ΔH_S). The investigated polymer was found to be rubbery at the test temperatures (glass transition temperature is about 17°C), but the detected permeabilities are comparable to those of the glassy polymers widely used for packaging applications. Data obtained in this investigation on samples exposed to moulding temperatures (240°C) for 3 min were compared to gas permeation data (presented in a previous paper) obtained for samples exposed at that temperature for 33 min in order to assess possible effects on gas transport properties. Water vapour transport was analysed by performing both sorption (35, 34, 55 and 65°C) and permeation (35°C) experiments at several activities. The analysis of sorption isotherms revealed the occurrence of water clustering, which was confirmed by a reduction of water diffusivity as a function of water concentration in the polymer.     

The effect of oxygen and the reduction temperature of the Pt/Al2O3 catalyst in enantioselective hydrogenation of 1-phenyl-1,2-propanedione

The effect of oxygen and catalyst reduction temperature in enantioselective hydrogenation of 1-phenyl-1,2-propanedione over commercial Pt/Al₂O₃ catalyst was investigated. Dichloromethane was used as solvent. The catalyst was modified in situ with (−)-cinchonidine. Relatively high enantiomeric excesses (65%) of (R)-1-hydroxy-1-phenyl-2-propanone were obtained with the solvent used as received, i.e. containing traces of dissolved oxygen and other impurities. Dichloromethane dissociated partially on the Pt/Al₂O₃ surface causing desorption of methane, ethene and HCl from the catalyst during TPD according to mass spectrometric analysis. Under anaerobic conditions the reaction rate was low giving only about 40% enantiomeric excesses of (R)-1-hydroxy-1-phenyl-2-propanone. When injecting 5 mm³ of oxygen into the reactor a beneficial effect was observed (i.e. higher reaction rate and enantiomeric excess) in comparison with anaerobic conditions. Poisoning effect of oxygen was observed when injecting 500 mm³ of oxygen into the reactor. Effect of catalyst reduction temperature was studied at three different temperatures (170, 400 and 455°C). Highest reaction rates and enantiomeric excesses were obtained with the catalyst reduced at 400°C. Methane was desorbed from the catalyst at temperatures between 263 and 383°C which could be the explanation for the lower activity of the catalyst reduced at 170°C. It was demonstrated that small amounts of oxygen can have a beneficial effect in enantioselective hydrogenation of 1-phenyl-1,2-propanedione and also that catalyst reduction temperature plays an important role in obtaining high enantiomeric excesses.     

Microstructural Evolution of Transparent PLZT Ceramics Sintered in Air and Oxygen Atmospheres

Transparent lanthanum-doped lead zirconate titanate (PLZT) ceramics were fabricated by air-pressure sintering. When the PLZT (9/65/35) specimens were sintered in air, the microstructure was not uniform throughout the body; the outer region near the surface was completely dense, while the inner region of the body was porous. The thickness of the outer dense layer increased parabolically with sintering time. When the specimen was sintered in air at 1200°C for 8 h, the thickness of the dense layer was ∼0.25 mm. Therefore, when the specimen had a thickness of <0.5 mm, it was dense and transparent. This difference in microstructure was attributed to the formation of lattice vacancies as a result of PbO evaporation from the surface. The sintering atmosphere also was important in determining the thickness of the dense layer. The thickness was strongly dependent on the oxygen partial pressure of the atmosphere. The oxygen-gas trapped in pores was deemed to migrate easily through the lattice vacancies. By sintering in an oxygen-gas atmosphere at 1200°C for 8 h, a transparent PLZT with thickness up to 2 mm was fabricated.     

Influence of synthesis process on the AC response of PLZT (8/65/35) ferroelectric ceramics

AC conductivity measurements have been carried out to study the dielectric characteristics of a ferroelectric PLZT (8/65/35). The initial powders were synthesized by two different methods: conventional mixed oxides and a chemical coprecipitation method. In both cases, the final ceramic bodies were obtained by an uniaxial hot-pressing step. The grain and grain boundary responses have been separated and a mixture of ionic-electronic conductivity was evaluated from the Arrhenius dependence. The preparation techniques led to different absolute conductivity values for each contribution (grain, σ_g, or grain boundary, σ_gb). The samples prepared by the mixed oxide method (MO) showed a higher bulk conductivity than those prepared by the coprecipitation method (CP). This result was explained taking into account the different concentration of charge carriers in MO than CP samples, influenced by the PbO content in the grain boundary. The dielectric analyses showed classical ordinary relaxor-dielectrics with a diffuse phase transition, which was markedly larger in the oxide-milled method (MO). The conductive mechanisms and their influence on the dielectric behavior were studied and led to the conclusion that they affect the dielectric permittivity measurements. The dielectric permittivity without the conductivity component showed a phase transition with lower dispersion for both preparation techniques.     

The NO selective reduction on the La1−xSrxMnO3 catalysts

La_1−xSr_xMnO₃ (x=0, 0.1, 0.3, 0.5, 0.7) perovskite-type oxides (PTOs) were prepared by coprecipitation under various calcination temperature, and their performances for the NO reduction were evaluated under a simulated exhaust gas mixture. The X-ray diffraction (XRD) and thermogravimetric analysis were carried out to find the formation process of the perovskite. The NO reduction rate under different reaction temperature, the concentration of oxygen and the presence of hydrocarbon were observed by the input/output analysis. In the presence of 10% excess oxygen, the catalyst La_0.7Sr_0.3MnO₃ calcined at 900 °C showed a NO reduction rate of 61% at 380 °C. The study of the reaction curves showed that C₃H₈ could act as the reducer for the NO reduction below 400 °C. The NO reduction is highly affected by increasing the O₂ concentration from 0.5 to 10%, especially at high temperatures when oxygen becomes more competitive than NO on the oxidation of C₃H₈, leading to a decrease of the NO reduction from 100% to zero at 560 °C.     

Effect of Li and Bi co-doping and sintering temperature on dielectric properties of PLZT 9/65/35 ceramics

In the present study, lead-lanthanum-zirconate-titanate (PLZT) ceramics were prepared by a solid-state mixed oxide method. Different amount of lithium carbonate and bismuth oxide (0.15 mol%, 0.45 mol% and 0.75 mol%), where the ratio of Li:Bi =1:1 by mole, was added to PLZT to investigate the effect of Li and Bi co-doping. The ceramic samples were sintered at the temperatures of 1000, 1050, 1100, 1150 and 1200 °C for 4 h. After that, all samples were subjected to phase identification, physical property determination (sintered density and microstructure) and dielectric property measurement. It was found that doping of 0.15 mol% Li and Bi resulted in maximum dielectric constant (ε_r =7819) when sintered at 1200 °C. Grain size of PLZT ceramics was dependent on sintering temperature and dielectric properties were affected by the chemical composition rather than the grain size of the ceramics. Therefore, co-doping of Li and Bi was useful as it could improve the dielectric properties of PLZT ceramics.     

Effect of composition and grain size on dielectric,ferroelectric and induced strain behavior of PLZT/ZrO2 composites

Lead lanthanum zirconate titanate ceramics (PLZT) are well known for their excellent dielectric, piezoelectric and ferroelectric properties. In this study, PLZT 9/70/30, 9/65/35 and 9/60/40 ceramics were prepared by vibro-milling mixed-oxide method. All compositions of powders were uniaxial pressed in pellets and sintered at the temperatures of 1200–1275 °C with various soaking times of 2, 4 and 6 h. The X-ray diffraction (XRD) patterns confirmed that all the PLZT samples had perovskite structure with ZrO₂ as a second phase and PLZT/ZrO₂ composite structure was formed. Dielectric behavior at the frequency of 1 kHz showed broad peak indicating relaxor ferroelectric behavior and the difference of the temperature at maximum dielectric at different frequencies increased when Zr:Ti ratio increased. Polarization with electric field (P-E loop) at room temperature showed that when Zr:Ti ratio increased, the coercive field decreased resulting from crystal structure change from tetragonal to rhombohedral. Induced strain with electric field depended on microstructure where the value of S_max/E_max tended to decrease with increasing grain size. It can be concluded that dielectric and ferroelectric behavior predominantly depended on composition of PLZT ceramics and induced strain behavior predominantly depended on grain size of PLZT ceramics.     

Fabrication of Optically Transparent Lead Lanthanum Zirconate Titanate ((Pb,La)(Zr,Ti)O3) Ceramics by a Three-Stage-Atmosphere-Sintering Technique

An easy technique has been developed to fabricate optically transparent lanthanum-modified lead zirconate titanate (PLZT) ceramics. This technique consists of three stages: (1) sintering in an oxygen atmosphere, (2) elimination of pores in a carbon dioxide atmosphere, and (3) elimination of oxygen vacancies in an oxygen atmosphere. The carbon dioxide atmosphere enhances the diffusion of oxygen from the pores to outside the sintered body. The experimental results reveal that use of a carbon dioxide atmosphere effectively decreases residual pores and improves optical transmittance. From commercially available raw powders, an optical transmittance of 51% (wavelength of 550 nm) can be achieved for 0.7 mm thick polished PLZT9/65/35 ceramics using a carbon dioxide atmosphere, whereas the value is only 34% without a carbon dioxide atmosphere. The advantage of this technique is that PLZT ceramics having high optical quality can be obtained using conventional sintering tools.     

Electrical conductance of KI in anhydrous acetonitrile

The electrical conductivity of KI solutions in anhydrous acetonitrile has been determined at 0, 25 and 35°C in the concentration range 0·9– 600 × 10⁻⁴ mole/l. The values of Λ₀, K and a calculated from the results are, respectively: 145·9 mho/cm, 0·95 × 10 ⁻² and 1·72 Å at 0°C; 186·2 mho/cm, 8·98 × 10⁻² and 4·6 Å at 25°C; and 204·8 mho/cm, 5·17 × 10⁻² and 3·5 Å at 35°C. The phoreograms at all the three temperatures are catabatic at lower concentration, but become anabatic at 0·017, 0·022 and 0·024 respectively, at 0, 25 and 35°C.     

Reduction of LaMnO3. Structural features of phases La8Mn8O23 and La4Mn4O11

Two new phases with ordered anion vacancies, La₈Mn₈O₂₃ and La₄Mn₄O₁₁, both having the general formula A_nB_nO_3n·1, form during the reduction of perovskites of the type LaMnO_3.07. The solid LaMnO_3.07, obtained in air at 1100°C and subsequently reduced in flowing carbon monoxide at 350°C, gives the stoichiometric perovskite LaMnO_3.00, whose reduction starts at 420°C and is completed at 450°C with formation of the phase La₈Mn₈O₂₃. The second reduction stage starts at approximately 500°C and is completed at 520°C with formation of La₄Mn₄O₁₁. The solids in the range of composition LaMnO_3.00-La₈Mn₈O₂₃ and La₈Mn₈O₂₃-La₄Mn₄O₁₁ would seem by X-ray examination to be biphasic but the behaviour during reduction is typical of a monophasic substance, the oxygen pressure of which at constant temperature progressively decreases as the composition tends to the limiting values La₈Mn₈O₂₃ and La₄Mn₄O₁₁. The crystal lattice of La₈Mn₈O₂₃ can be considered as resulting from a sequence of seven octahedral sheets, MnO₆, alternated with tetrahedral sheets, MnO₄, and the crystal lattice of La₄Mn₄O₁₁ from a sequence of three MnO₆ sheets alternating with MnO₄ sheets.     

Investigation of a Ba0.5Sr0.5Co0.8Fe0.2O3−δ based cathode SOFC: II. The effect of CO2 on the chemical stability

The effect of carbon dioxide on the chemical stability of a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ cathode in the real reaction environment at 450 °C was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), temperature programmed desorption (TPD), X-ray diffraction (XRD) and electrochemical impedance spectra (EIS) techniques. It was found that the presence even of very small quantities of CO₂ seriously deteriorates the fuel cell performance at 450 °C. XPS, TPD and XRD results strongly evidenced the formation of carbonates involving strontium and possibly barium after the BSCF cathode was operated in 1% CO₂/O₂ gas mixture at 450 °C for 24 h. SEM-EDX analysis of the BSCF cathode surface, after treatment in CO₂/O₂ environment at 450 °C, showed small particles on the surface probably associated with a carbonate phase and a segregated phase of the perovskite. The corresponding EDX spectra confirmed the presence of a carbonate layer and also revealed the surface enrichment of strontium and barium elements. EIS results indicated that both ohmic and polarization resistances increased gradually with the introduction of carbon dioxide in the oxidant stream, which could be interpreted by the decreased oxygen reduction kinetics and the formation of carbonate insulating layer.