The role of drying-control chemical additives on the preparation of sol-gel derived PLZT thin films

Films of Pb _x/100La _x/100(Zr _y/100Ti _z/100)_1–x/400O₃ with x=8, y=65 and z=35 (PLZT(8/65/35)) with a single perovskite structural phase were successfully prepared by using drying-control chemical additives in sol-gel processing followed by rapid thermal annealing at 600 °C for only 1 min on Si(Pt) substrates. The roles of the drying-control chemical additives ethylene glycol and formamide in the gel preparation were studied. The hysteresis loop of PLZT(8/65/35) thin film was measured. The remanent polarization and coercive field were found to be about 1.3 C cm^–2 and 15 kVcm^–1, respectively.     

Dielectric relaxations in SrTiO3 doped with La2O3 and MnO2 at low temperatures

In addition to the dielectric relaxation around 170 K in the cubic structure of Sr_1–3x/2La _x TiO₃, a similar relaxation was observed at about 70 K in the tetragonal structure with an activation energy in the range 0.13–0.16 eV which increases as x in Sr_1–3x/2La _x TiO₃ varies from 0.60–3.00 at%. This relaxation is explained by Skanavi's model and is discussed in terms of thermal motions of Ti⁴⁺ between potential minima produced by lattice distortions in the tetragonal structure. In order to provide a direct evidence for the suggestion that the dielectric relaxation around 170 K in the cubic is due to thermal motions of Ti⁴⁺, dielectric properties on manganese-doped specimens, Sr_1–3x/2La _x Mn _y Ti_1–y ),O₃ with x=1.40×10^–2 and y=0.1×10^–2, were investigated because Mn⁴⁺ substitutes for Ti⁴⁺. As well as the relaxation due to Ti⁴⁺, this specimen exhibits another peak due to Mn⁴⁺ with an activation energy somewhat smaller than that of Ti⁴⁺. The activation energies and the relative intensity of these relaxation processes are explained by the difference in ionic radii of Mn⁴⁺ and Ti⁴⁺ and the difference in formation energies of a strontium vacancy adjacent to Mn⁴⁺ and that to Ti⁴⁺, which were calculated theoretically using a shell model.     

Coprecipitation-assisted hydrothermal synthesis of PLZT hollow nanospheres

Lanthanum-modified lead zirconate titanate Pb_1−xLa_x(Zr_1−yTi_y)O₃ (PLZT) hollow nanospheres have been successfully prepared via a template-free hydrothermal method using the well-mixed coprecipitated precursors and the KOH mineralizer. The structure, composition, and morphology of the PLZT hollow nanospheres were characterized by XRD (X-ray diffraction), ICP (inductive coupled plasma emission spectrometer), FTIR (Fourier transform infrared spectra), TG/DTA (thermogravimetric analysis and differential thermal analysis), TEM (transmission electron microscopy) and SEAD (selected area diffraction). The results show that the composition and the morphology control of the PLZT products are determined by the KOH concentration. The PLZT hollow nanospheres with uniform size of about 4 nm were synthesized in the presence of 5 M KOH. The crystalline nanoparticles can be prepared at dilute KOH, in contrast to the amorphous powders prepared at concentrated KOH. Formation mechanisms of the PLZT hollow nanospheres are also discussed.     

Synthesis of compositionally homogeneous Pb(ZrxTi1−x)1−y(Mg1/3Ta2/3)yO3 by wet–dry combination method and its dielectric properties

Ternary perovskite-type solid solutions of Pb(Zr_xTi_1−x)_1−y(Mg_1/3Ta_2/3)_yO₃ (PZTMT) were synthesized by a wet–dry combination method in which a coprecipitation process was applied to B-site cations (Zr⁴⁺, Ti⁴⁺, Mg²⁺ and Ta⁵⁺). The compositional homogeneity in calcined powders and dielectric properties of sintered ceramics were investigated. The powder X-ray diffraction analysis revealed that PZTMT powders prepared by the wet–dry combination method had no compositional fluctuation unlike that prepared by a conventional dry method. The sintered PZTMT prepared by the wet–dry combination method exhibited much higher dielectric constant than that prepared by the conventional dry method. The improvement of the compositional homogeneity and the density led to the improvement of the dielectric properties.     

Microstructure and electrical characterisations of K-modified PLZT

Potassium-modified PLZT [Pb_0.92(La_{1 – z}K_z)_0.08(Zr_0.60Ti_0.40)_{0.98 + 0.04z}O₃ (z = 0.0, 0.1, 0.3, 0.5, 0.7)] ceramics were synthesised using sol-gel technique. Preliminary structural and microstructural parameters were determined using XRD, SEM and TEM techniques. Detailed studies of dielectric properties at 10 kHz in a wide temperature range suggest that the compounds have diffuse phase transition of second order. Studies of spontaneous polarisation, pyroelectric and piezoelectric properties yielded data for devices.     

Microstructure, dielectric and electromechanical properties of PLSZFT nanoceramics for piezoelectric applications

This investigation highlights the influence of isovalent Sr²⁺ on acceptor Fe³⁺ modified PLZT for microstructure and its effect on dielectric and piezoelectric properties [Pb_0.985−yLa_0.015Sr_y][(Zr_0.538Ti_0.462)_0.985Fe_0.015]O₃ where y = 0, 0.5, 1.0, and 1.5 mol% nanocrystalline solid solutions near morphotrophic phase boundary were synthesized by solid state reaction method. X-ray diffraction patterns indicated that Sr increment resulted in strong tetragonality. Grain size and apparent density enhanced up to y = 1.5 mol%. TEM studies indicated that average particle size ranged from 23 to 68 nm. PLSZFT compositions attained optimum ε_RT, d₃₃, and k_p at y = 1.5 mol%, respectively which could be suitable for possible piezoelectric applications. The influence of grain size on dielectric and piezoelectric properties are reported.     

Synthesis and characterization of some PLNZT ceramics

Powder of sodium doped polycrystalline samples of PLZT with composition Pb_0.98(La_{_1–x/3}Na _x )_0.02(Zr_0.53 Ti_0.47)_0.9950·O₃ (PLNZT) with x=0.5 was systematically prepared using spray drying technique. Rhombohedral phase of PLNZT compound has been confirmed after being calcined at 800 °C. DTA–TGA and XRD studies were used to characterize the compound synthesized. SEM was used for micro-structural evaluation. The dielectric constant () and loss tangent (tan ) of the compound were studied at different temperatures at 10 kHz frequency, which suggests that the compound undergoes a ferro-electric phase transition of diffuse type.     

Large electric field-induced strain near AFE/FE phase boundary in (Pb0.97La0.02)(Zr, Sn, Ti)O3 system

(Pb_0.97La_0.02)(Zr, Sn, Ti)O₃ ceramics were prepared by conventional solid state reaction process, and the effects of Zr⁴⁺/Sn⁴⁺ and Zr⁴⁺/Ti⁴⁺ ratios on the crystal structure, dielectric, ferroelectric, and electric field-induced strain properties were systemically investigated. The XRD results showed, with the increase of Zr⁴⁺ and Ti⁴⁺ contents, the stability of the specimens became weakened and a transformation from AFE to FE phase was observed at x = 0.65 and y = 0.12, respectively. In addition, it was observed that the strain first increased with a maximum value in the composition near AFE/FE phase boundary, and then decreased with increasing Zr⁴⁺ and Ti⁴⁺ contents. Further, with the decrease of measuring frequency, the strain continuously increased because the reversal of the domain can be more sufficient. The maximum strain of 0.55 % is obtained in Pb_0.97La_0.02(Zr_0.63Sn_0.26Ti_0.11)O₃ AFE ceramics at 1 Hz measuring frequency which lays a foundation for preparing actuators with high properties.     

Effect of the addition of Ca2+ on the structure, microstructure and ferroelectric properties of (Pb1 − y Ca y )(Zr0.8Ti0.2)O3 system with y = 0.0, 0.02, 0.05 and 0.1

This work studies the relationship between ferroelectric properties and structural features of the (Pb_{1 – y} Ca _y )(Zr_0.8Ti_0.2)O₃ system with y = 0.0, 0.02, 0.05 and 0.1. All of the samples were prepared by hot-pressing of PZT calcined powder, prepared by conventional ceramic route. Single phase compositions of rhombohedral (RH) structure were observed for the whole series of the samples studied in this work. However, a linear decrease of RH lattice constant a _p is seen with increasing the Ca²⁺ concentration with a subsequent decrease of lattice strain expressed by (90 – _p). Further, a sharp decline is also observed in the magnitudes of saturation polarization (P _s) of the samples doped with 2 mol% Ca²⁺. However, the rate of decrease slows down for Ca²⁺ concentrations above this level. A diffuse phase transition was observed in the case of 10 mol% Ca²⁺-doped PZT(0.8) which is believed to be possibly due to the distribution in coupling strengths created from a random compositional fluctuations of Ca²⁺ and Pb^2– ions on A-sites. The results are interpreted on crystal-chemical grounds. It is proposed that the long range coupling of (Zr/Ti)O₆ coordination octahedra and Pb²⁺ ions, due to the covalency of the Pb–O bond, is interrupted by the incorporation of Ca²⁺. By considering the effect of calcium on coupling strength and coupling distribution, the observed dielectric response for the above compositions is qualitatively explained.     

Incorporation of bismuth into Ba6− x R8+2/3x Ti18O54(R = Nd, Gd)

Microstructural investigations and microanalyses of a series of Ba_6–x R _8+2/3x Ti₁₈O₅₄ ceramics (R = Nd, Gd) revealed that the solid-solubility limit for the isovalent substitution of R ³⁺ by Bi³⁺ depends on the composition of the Ba_6–x R _8+2/3x Ti₁₈O₅₄ phase. For the Nd analogue the solid-solubility limit (y in Ba_6–x (Nd_1–y Bi _y )_8+2/3x Ti₁₈O₅₄) decreases with a decrease in x from y = 0.16 for x = 2.0 to y = 0.10 for x = 0.8. An even lower solid-solubility limit (y = 0.06) was found for the Ba_4.5(Gd_1–y Bi _y )₉Ti₁₈O₅₄ compound (x = 1.5). All substituted Nd compositions exhibit higher permittivities (93–99), lower temperature coefficients of permittivity (11–15 ppm/K) and higher dielectric losses (Q · f = 1300–5500 GHz) than the parent compositions. By exceeding the solid-solubility limit, abrupt changes in the microstructural and dielectric characteristics are induced.     

Dielectric, ferroelectric and piezoelectric properties of (1 − x)[Pb0.91La0.09(Zr0.60Ti0.40)O3]–x[Pb(Mg1/3Nb2/3)O3], 0 ≤ x ≤ 1

The dielectric, ferroelectric, and piezoelectric properties of ceramic materials of compositions (1 − x)[Pb_0.91La_0.09(Zr_0.60Ti_0.40)O₃]–x[Pb(Mg_1/3Nb_2/3)O₃], x = (0, 0.2, 0.4, 0.6, 0.8, and 1.0) were studied. The above compositions were prepared by mixing the individual Pb_0.91La_0.09(Zr_0.60Ti_0.40)O₃ (PLZT) and Pb(Mg_1/3Nb_2/3)O₃ (PMN) powders in order to design materials with different combination of piezo and dielectric properties. The powders were calcined at 850 °C for 4 h. The presence of various phases in the calcined powders was characterized by X-ray diffraction (XRD) technique. The compacts were prepared by uniaxial pressing and were sintered at 1250 °C for 2 h. The sintered compacts were electroded, poled at 2 kV/mm dc voltage and their dielectric, ferroelectric, and piezoelectric properties were measured. In general, it was observed that the dielectric constant, loss factor and the slimness of the ferroelectric curves increase with the PMN content while the remnant polarization, saturation polarization, and the coercive fields were decreased. It is now possible to design materials with a wide combination of d ₃₃, K, and loss factor by varying PLZT and PMN ratio.     

Synthesis and characterization of Fe3+-modified PLZT ferroelectrics

Fe³⁺-modified nanocrystalline PLZT, i.e., Pb_0.92[La_1–z Fe _z ]_0.08[Zr_0.60Ti_0.40]_0.98O₃ (PLFZT) (z=0.0, 0.3, 0.6, 0.9, 1) materials were synthesized by a high-temperature solid-state reaction technique. X-ray studies of the compounds confirmed the formation of single-phase, ultrafine (nano-sized) and homogeneous materials. Microstructural scanning electron microscopy (SEM) study shows the uniform distribution of smaller grains on the surface of the samples. Detailed dielectric studies of the compounds as a function of temperature (30–450 °C) show that the broadening of the permittivity peak and transition temperature depends on Fe³⁺-ion concentration. Analysis of diffuseness () of the broadened dielectric peaks of the materials gave its value between 1 and 2, indicating the different degrees of substitutional disorder in the system. The increase in Fe³⁺-substitution at the La-site of PLZT shows many interesting and unusual dielectric relaxor behaviors of the compounds. The transition temperature T _c of PLZT (8/60/40) ferroelectric shifts towards a higher temperature region on increasing Fe³⁺ concentration. The variation of d.c. and a.c. electrical conductivity of the material with temperature shows its semiconducting behavior; and hence the materials can be used for some electronic devices.     

Dielectric behaviour of spray dried Pb0.98(La1?x/3Nax)0.02(Zr0.53Ti0.47)0.9950O3 system

Sodium modified PLZT, Pb_0.98(La_{1 – x/3}Na_x)_0.02(Zr_0.53Ti_0.47)_0.9950O₃ (PLNZT) with x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, ceramics have been synthesized by spray drying technique. Rhombohedral phases of PLNZT ceramics were confirmed by XRD. Pellets prepared from the calcined powders were sintered at 1100°C. Micro-structural studies show the grains were spherical and homogeneous. Dielectric behaviour of these compounds has been studied as a function of temperature at 10 KHz frequency. Diffusivity of these compounds calculated from -T plots were found to lie between 1 and 2, which suggests that the compounds have diffuse phase transition (DPT). The dielectric constant () as found to increase initially upto x = 1.5 and then to decrease with increasing Na—concentrations.     

Microstructure modifications and modulated piezoelectric responses in PLZT/Al2O3 composites

Piezoelectric ceramics for acoustic applications have been prepared by mixing the piezoelectric phase Pb_1−1.5xLa_x□_x/2(Ti_1−yZr_y)O₃ (PLZT) with variable fractions of Al₂O₃. The samples are in form of pellets and polarized at high temperature. After thermal treatment, X-ray diffraction and scanning electron microscopy have been used to determine the phase and morphological modifications. The morphotropic PLZT initial phase disproportionates into modified PLZT and ZrO₂ phases. Using electrical impedance spectroscopy, the resonance frequencies of the composite system have been determined and analyzed. As the Al₂O₃ volume fractions increase, the resonance frequency and the amplitude of the electrical response both decrease. An interpretation of the role of Al₂O₃ additions is proposed in terms of phase and microstructure modifications. Using LRC electrical equivalent circuits, the impedance variations close to the resonance frequency are modeled: the increase of the resistance R (electrical losses) and of the capacitance C are respectively correlated to the change in microstructure and in nature of PLZT initial phase.     

Microstructural and dielectric properties of donor doped (La3+) CaCu3Ti4O12 ceramics

The effect of La³⁺ doping on Ca²⁺ sites in CaCu₃Ti₄O₁₂ (CCTO) was examined. Polycrystalline samples in the chemical formula Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ with x = 0, 0.5, 1 were synthesized via the conventional solid state reaction route. X-ray powder diffraction analysis confirmed the formation of the monophasic compounds and indicated the structure to be remaining cubic with a small increase in lattice parameter with increase in La³⁺ doping. The dielectric and impedance characteristics of Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ were studied in the 100 Hz–10 MHz frequency range at various temperatures (100–475 K). A remarkable decrease in grain size from 50 μm to 3–5 μm was observed on La³⁺ substitution. The dielectric constant of CaCu₃Ti₄O₁₂ decreased drastically on La³⁺ doping. The frequency and temperature responses of dielectric constant of La³⁺ doped samples were found to be similar to that of CaCu₃Ti₄O₁₂. The effects of La³⁺ doping on the electrical properties of CaCu₃Ti₄O₁₂ were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La³⁺ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La³⁺ doped CCTO ceramics were unambiguously established by modulus spectra studies.     

Growth and fatigue properties of pulsed laser deposited Pb1 − x La x (Zr y Ti z )O3 thin films with [0 0 /] preferred orientation

Growth of [0 0 /] preferentially oriented Pb_{1 - x} La _x (Zr _y Ti _z ) O₃ (PLZT) thin films was carried out by using targets of either tetragonal or rhombohedral structure. The tetragonal films grew in a similar manner to the rhombohedral films. Both the substrate temperature (500 or 550 C) and oxygen pressure (0.1 mbar, 10 Pa) required stringent control in order to deposit [0 0 /]-textured PLZT thin films. The ferroelectric and fatigue properties were examined.The films deposited on YBa₂Cu₃O_{7 - x} and CeO₂ coated silicon (YBCO/CeO₂/Si) substrates possessed substantially lower remanent polarization than those grown on YBCO coated SrTiO₃ (YBCO/STO) substrates; this is ascribed to inferior crystallinity of the PLZT/YBCO/CeO₂/Si films. The remanent polarization of tetragonal PLZT films was degraded insignificantly up to 10⁸ polarization switching cycles, whereas that of rhombohedral PLZT films was already reduced to 80% of the initial value after 10⁸ cycles. Low endurance of rhombohedral films was ascribed to the periodic stress induced when the inclined spontaneous polarization vector (P = [111]) switched. On the other hand, high endurance of tetragonal films was explained by the fact that the spontaneous polarization vector (P = [001]) lies along the film's normal such that switch cycles cause no lateral stress.     

A study of the stabilization of aluminium titanate

A tialite ceramics (Al₂TiO₅) was synthesized at a temperature of 1500 °C, incorporating CaF₂, La₂O₃, SiO₂ or kaolin and MgO additives. Its thermal stability was investigated by thermocycling in a reducing medium. The batches containing SiO₂ or kaolin additives underwent a decomposition to rutile and corundum. A stabilized ceramic with added MgO was produced. X-ray and electron-probe microanalysis established the presence of Mg/Al, Ti_z/O₄, Al_2–x-y Ti_1+x Mg _y O₅ and Ca_1–x La _x /Al_12–y-z Mg _y Ti _z /O₁₉ solid solutions, which retained their chemical composition after thermocycling in a reducing medium.     

La3+ effect on dipole ordering in Pb1 ? xLax[Zr0.7Sn0.2Ti0.1][1 ? x/4]O3(0 < x ≤ 0.03) solid solutions

We have studied temperature- and electric-field-induced phase transitions in ceramic samples of Pb_{1 − x} La _x [Zr_0.7Sn_0.2Ti_0.1]_{1 − x /4}O₃ (0 < x ≤ 0.03) solid solutions. The results indicate that La³⁺ doping to x > 0.005 impedes long-range dipole-dipole interactions and stabilizes nonpolar phases below the Curie temperature. At a constant La³⁺ concentration, lowering the temperature facilitates a field-induced transition to a ferroelectric state. In thermally depoled samples, the first antiferroelectric → ferroelectric switching usually requires a higher bias voltage than do subsequent switchings. Original Russian Text ? E.A. Bikyashev, E.A. Reshetnikova, M.I. Tostunov, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 8, pp. 990–995.     

Superconductivity of La2−x Sr x CuO4 with high strontium concentration by sulphur doping

The effects of sulphur substitution for oxygen on the structure and properties of nonsuperconducting La_2–x Sr _x CuO₄, where x=0.26 and 0.30, have been studied. In La_2–x Sr _x CuO _4–y -S _y , the sulphur-doped samples exhibit superconducting transition at 37–39 K and a larger Meissner effect than undoped samples. It was found that the superconductivity of La_2–x Sr _x CuO_4–y S _y is apparently determined by the value of x–y and the strontium concentration region in which La_2–x Sr _x CuO₄ shows superconductivity shifts to higher strontium concentrations with sulphur doping.     

Mechanism of grain growth and excellent polarization,dielectric relaxtion of La<Superscript>3+</Superscript>, Nd<Superscript>3+</Superscript> modified PZT nano-films prepared by sol–gel technique

Ferroelectric PbZr_0.52Ti_0.48O₃ film and its partial substitutions by rare earth ions La³⁺ and Nd³⁺ Pb_0.9(La/Nd)_0.1Zr_0.52Ti_0.48O₃, grown on Pt(111)/Ti/SiO₂/Si(100) substrates, were prepared via sol–gel and rapid thermal processes. Structural characterization by X-ray diffraction and scanning electron microscopy showed that Pb(Zr_0.52Ti_0.48)O₃ and Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ films are of (111) preferred orientation but Pb_0.9Nd_0.1(Zr_0.52Ti_0.48)O₃ is more inclined to (100) reflection though both are of tetragonal perovskite structure. The results indicate that the piezoelectric properties of PZT thin films can be improved by doping La³⁺ and Nd³⁺ substituted A-site. The d₃₃ can be dramatically improved by doping La³⁺. Moreover, Pr of Pb(Zr_0.52Ti_0.48)O₃ films reaches up to 120.53 µC/cm², while the doping samples present relatively inferior ferroelectric hysteresis loops (Pr_La?=?64.32, Pr_Nd?=?53.17 µC/cm²), greater dielectric constants, higher dielectric loss and lower leakage current than the undoped Pb(Zr_0.52Ti_0.48)O₃ sample. And meanwhile, the samples showed a typical non-Debye dielectric spectroscopy of multiple quantum relaxation time distribution observing from the Cole–Cole plot at room temperature.