A novel route to perovskite lead zirconate titanate from glycolate precursors via the sol–gel process

A perovskite lead zirconate titanate was synthesized by the sol‐gel process, using lead glycolate, sodium tris(glycozirconate) and titanium glycolate as the starting precursors. For the mole ratio Pb:Zr:Ti of 1:0.5:0.5 [Pb(Zr_0.5Ti_0.5)O₃], TGA‐DSC thermal analysis indicated that the percentage of ceramic yield was 55.8, close to the calculated chemical composition value of 49.5. The exothermic peak occurred at 268 °C below the theoretical Curie temperature of 400 °C. The pyrolysis of Pb(Zr_0.5Ti_0.5)O₃ of the perovskite phase was investigated in terms of calcination temperature and time. The structure obtained was of the tetragonal form when calcined at temperatures below 400 °C; it transformed to the tetragonal and the cubic forms of the perovskite phase on calcination above the Curie temperature, as verified by X‐ray data. The lead zirconate titanate synthesized and calcined at 400 °C for 1 h had the highest dielectric constant, the highest electrical conductivity and the dielectric loss tangent of 10 190, 0.803 × 10^?3 (Ω.m)^?1 and 1.513 at 1000 Hz, respectively. The lead zirconate titanate powder synthesized has potential applications as an electronic material. Copyright © 2008 John Wiley & Sons, Ltd.     

A novel route to perovskite lead zirconate from lead glycolate and sodium tris(glycozirconate) via the sol–gel process

A perovskite lead zirconate was synthesized, using lead glycolate and sodium tris (glycozirconate) as the starting precursors, by the sol–gel process. The obtained molar ratio Pb:Zr of PbZrO₃ was 0.9805:1. The TGA–DSC characterizations indicated that the percentage of ceramic yield was 56.4, close to the calculated chemical composition of 59.6. The exothermic peak occurred at 245.7 °C, close to the theoretical Curie temperature of 230 °C. The pyrolysis of PbZrO₃ of the perovskite phase was investigated in terms of calcination temperature and time. The structure obtained was the orthorhombic form when calcined at low temperature at 300 °C for 1 h; it transformed to the monoclinic and cubic forms of the perovskite phase at higher temperatures above the Curie temperature as verified by X‐ray data. The lead zirconate synthesized and calcined at 300 °C for 1 h has the highest dielectric constant, the highest electrical conductivity and the dielectric loss tangent of 2267, 3.058 × 10^?4 (Ω m)^?1 and 2.484 at 1000 Hz, respectively. The lead zirconate powder produced has potential applications as materials used in microelectronics and microelectromechanical systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Electrorheology and characterization of acrylic rubber and lead titanate composite materials

Oxide one‐pot synthesis was used to synthesize a polymer precursor to lead titanate, PbTiO₃. Perovskite lead titanate, PbTiO₃, was synthesized via the sol–gel process. The dielectric constant, electrical conductivity and loss tangent of our acrylic rubber (AR71)–lead titanate (PT) composite material (AR/PT_8) were 14.15, 2.62 × 10^?7/Ω m, and 0.093, respectively, measured at 27 °C and 1000 Hz. SEM micrographs of composites between the AR71 elastomer and PbTiO₃ showed that the particles were reinforced within the matrix. The electrorheological properties of the AR71/PT composites were investigated as functions of electric field strength from 0 to 2 kV/mm and PbTiO₃ particle volume fraction. The storage modulus increased linearly with particle volume fraction, with or without an electric field. Without an electric field, the particles merely acted as a filler to absorb or store additional stress. With the electric field on, particle‐induced dipole moments were generated, leading to interparticle interactions, and thus a substantial increase in storage modulus. With PbTiO₃ particle volume fractions as small as 10^?4 embedded in the elastomer matrix, the modulus increased by nearly a factor of 2 as the electric field strength varied from 0 to 2 kV/mm. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural development and kinetic analysis of PbTiO3 powders processed at low-temperature via new sol-gel approach

The synthesis of crystalline lead titanate powder by a generic low-temperature sol-gel approach is developed. Acetoin was added as ligand, instead of the commonly used alkanolamines, to ensure total dissolution of the precursor compounds. The feasibility of the acetoin-Ti isopropoxide complex as a new precursor of PbTiO₃ perovskite particles via sol-gel method has been demonstrated. No excess lead has been introduced. Nanometric PbTiO₃ crystallites have been formed at 400 °C under atmospheric pressure from titanium isopropoxide and lead acetate in alcoholic solution by remarkably low activation energy of crystallization process of 90 kJ mol⁻¹. The powders show tetragonal lattice and dendritic morphology. In addition to the effect of heat-treatment temperature, time, and atmosphere, the sol chemistry particularly influenced the phase composition, particle size, and particle morphology. The use of different ligands significantly modified powder morphology. The extent of the crystallization was quantitatively evaluated by differential thermal analysis and analyzed by Johnson-Mehl-Avrami approach. The crystallization followed two rate regimes depending on the interval of the crystallized fraction.     

Fabrication of lead titanate single crystalline nanowires by hydrothermal method and their characterization

Single crystalline nanowires of lead titanate (PbTiO₃) were fabricated by hydrothermal method at 200°C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure and optical properties of PbTiO₃ nanowires were investigated. The PbTiO₃ nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO₃ with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm. The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies are responsible for the light emission of PbTiO₃ nanowires.     

Elaboration par voie sol-gel et caracterisation de materiaux ceramiques PbTiO3 dopes au lanthane

Preparation and characterization of sol-gel derived La-doped PbTiO₃ ceramics. La-doped lead titanate bulk powders of perovskite type were prepared by a sol gel process. An excess of lead (5%) was added in order to compensate the Pb losses during the annealing process. The effect of temperature on the evolution of the powders was studied using Fourier Transform Infrared (FTIR) spectroscopy, Thermal Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and X-Ray Diffraction (XRD). The effect of La-doping concentration on the crystal structure was also investigated. The La-doped lead titanate bulk powders (PLT) annealed at 600°C for 2h crystallize in a perovskite phase with cubic structure.     

The differential thermal analysis behavior of lead zirconate titanate materials

Differential thermal analysis has been used to examine the reactions involved in the formation of lead zirconate titanate and related materials. The reaction of PbO and TiO₂ produced an exothermic peak near 600°C, while mixtures of PbO and ZrO₂ gave endothermic peak at 760°C. Lead titanate and lead zirconate mixtures showed no evidence of reaction below 900°C. Evidence is presented which suggests that PbO and PbTiO₃ react in the vicinity of 750°C. For ternary mixtures of PbO, titanate, the thermograms indicate a complicated behavior between 600–800°C, depending on the ratios of the reactant materials. The results suggest that the calcination reaction to form lead zirconate titanate is a more complex process than has been recognized. Data on the various phase transitions for the lead zirconate titanate materials are also presented.     

Hydrothermal Synthesis and Phase‐, Morphology‐Evolution Mechanism of Lead Titanate Nanostructures Assisted with Tetramethylammonium Hydroxide

Lead titanate nanostructures with different phases and morphologies, layered hexagonal PbTiO₂(CO₃)_0.3‐ (NO₃)_0.35(OH) nanosheets, pyrochlore Pb₂Ti₂O₆ nanodendites, pre‐perovskite PbTiO₃ nanofibres and perovskite PbTiO₃ nanoplates, have been synthesized via a conventional hydrothermal route assisted with different concentrations of tetramethylammonium hydroxide (TMAH). X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high‐resolution TEM (HRTEM) were employed to characterize the phase, morphology and growth behavior of the synthesized samples. The results reveal that at low TMAH concentration the obtained samples are mainly of PbTiO₂(CO₃)_0.3(NO₃)_0.35(OH) nanosheets. With the TMAH concentration increasing, the obtained samples change to pyrochlore Pb₂Ti₂O₆ nanodendites, pre‐perovskite PbTiO₃ nanofibres and perovskite PbTiO₃ nanoplates in turn. With the basis of the experimental results, the phase‐ and morphology‐evolution mechanism of the lead titanate nanostructures is discussed by combining the analysis of the lattice structure feature and the properties of TMAH.     

Sol–gel based synthesis of ultrafine tetragonal BaTiO3

Ultrafine tetragonal BaTiO₃ nanocrystals have been prepared by a sol–gel based method. By adjusting the volume ratio of H₂O/DEG (diethylene glycol) in the solutions, hydrolysis rate of tetra-n-butyl titanate was strongly inhibited and the particle size could be controlled as small as 4–8 nm. The powder X-ray diffraction and transmission electron microscopy characterizations exhibit that the nanocrystals are spherical and well crystallized. The Raman spectrum shows the products are composed of the orthorhombic phase and tetragonal phase. The Fourier transform infrared spectrum revealed that a surface modification layer was formed around the BaTiO₃ nanocrystals, which can prevent them from aggregation and help to form a stable, high solid content sol.     

Chloro-free route to mixed-metal oxides. Synthesis of lead titanate nanoparticles from a single-source precursor route

A new heterobimetallic nitrilotriacetatoperoxotitanate complex of titanium and lead [Pb(H₂O)₃]₂[Ti₂(O₂)₂O(nta)₂]·4H₂O (C₆H₆O₆N=H₃nta) was isolated in pure crystals directly from the solution containing tetrabutyl orthotitanate, hydrogen peroxoide, lead acetate, and nitrilotriacetic acid at pH = 2.0–4.0. The isolated complex was characterized by elemental analyses, IR spectrum, thermal analysis (TG), and single-crystal X-ray diffraction. The single-crystal X-ray structural analysis revealed that the titanium atom is N,O,O′,O′′-chelated by the nitrilotriacetate and O,O′-chelated by the peroxo group and was coordinated to the bridging O atom in an overall pentagonal-bipyramidal geometry. The thermal decomposition of this precursor led to the formation of phase-pure lead titanate (PbTiO₃) at ≥450 °C. The morphology, microstructure, and crystalline of the resulting PbTiO₃ product have been characterized by BET, transmission electron microscopy, and powder X-ray diffraction. The TEM micrographs revealed that the size of the as-synthesized crystallines to be 50–100 nm range. The BET measurement revealed that the PbTiO₃ powders had a surface area of 5.6 m²/g.     

Structural and Electrical Properties of Sol–Gel-processed CdTiO3 Powders and Films

Cadmium titanate, CdTiO₃, was prepared by the sol–gel technique in bulk and in thin film form. The thermal evolution of the gels and the phase changes were studied by thermo- gravimetric analysis (TGA), X-ray diffractometry (XRD) and Raman and energy-dispersive (EDS) spectroscopies. The morphology of the samples was observed using scanning electron microscopy (SEM). Gels heated to 800 °C gave rise to powders with only the ilmenite-like phase. The orthorhombic perovskite phase is the only crystalline phase observed after a 4 h heat-treatment at 1100 °C. With respect to the conventional preparation method by solid-state reaction, by the sol–gel method it is possible to prepare the ilmenite phase at lower temperatures and the perovskite phase in a shorter time. Clear, homogeneous thin films were obtained by the dip-coating method. The refraction index and the thickness of the films were measured using ellipsometry. The humidity-sensitive electrical properties were measured for thin films deposited on alumina substrates with comb-type gold electrodes, heated to 200 °C and 450 °C. The films heated to 200 °C, which still contained organics, showed a variation of the resistance of six orders of magnitude in the relative humidity (RH) range tested (4–87% RH). The films heated to 450 °C, made of ilmenite-type CdTiO₃, were nearly insensitive to RH. © 1997 by John Wiley & Sons, Ltd.     

Structure and Dielectric Properties of NiTiO3 Powders Synthesized by the Modified Sol–Gel Method

This study reports the synthesis of nickel titanate (NiTiO₃) powders by using the modified sol‐gel method, with nickel acetate tetrahydrate as the nickel source, titanium isopropoxide as the titanium source, and 2‐methoxyethanol as the solvent, followed by post‐heat treatment in air at temperatures ranging from 500 °C to 900 °C. The characteristics of powders were determined by X‐ray diffraction (XRD), FT‐infrared spectroscopy (FT‐IR), ultraviolet/visible spectroscopy (UV/Vis), and Raman spectroscopy. The particle size and surface area of the powders were also measured. The results indicated that single‐phase NiTiO₃ can be prepared using the modified sol‐gel method, followed by post‐heat treatment at the relatively low temperature of 550 °C. The crystallite sizes and particle sizes of NiTiO₃ powders increase in conjunction with the post‐heat treatment temperatures. However, the surface area of the powders shrinks as the post‐heat treatment temperatures increase. The dielectric constants of NiTiO₃ powders, based on the capacitance‐voltage analysis, are within a range of 13.2 to 17.8.     

Heterometallic lead-titanium oxyalkoxide precursors to lead titanate thin films

Two lead titanium oxyalkoxides with composition Pb₂Ti₄O₂(O₂CCH₃)₂(OC₂H₅)₁₄ and Pb₂Ti₂O₂(O₂CCH₃)₂(OCH(CH₃)₂)₈ have been isolated and characterised by elemental analysis, IR, ²⁰⁷Pb NMR and molecular weight measurements. X-ray structural analysis of the 1:2 complex confirmed the presence of two Pb₂Ti₂O units which are linked by a common Pb···Pb edge and are held together by alkoxide and acetate bridges. The acetate groups have migrated from the Pb to the Ti centres during the reaction. Hydrolysis of the 1:1 Pb/Ti complex produced clear gels providing the H₂O/complex ratio was less than 4. Heat treatment of the gel results in loss of residual organics below 400°C. The XRD pattern indicates the presence of the pyrochlore and perovskite phases after heating at 500°C but the sample is poorly crystalline. Complete conversion to the perovskite phase of lead titanate occurs on heating to 600°C for 1 hour. Thin films of lead titanate were deposited by dip-coating a solution of this complex in isopropanol. Analyses of the films, carried out using electron microprobe, Scanning Auger Spectroscopy and Rutherford Backscattering, indicated that they were of excellent quality, crystalline after heating at 600°C and with relatively sharp substrate-coating interface.     

Combined methane reforming over nano LaNiO<Subscript>3</Subscript> catalyst with modified active surface

In this study, nano catalyst LaNiO₃ with perovskite structure was synthesized using the citrate sol–gel method in the combined methane reforming with CO₂ and O₂ (CRM). The effects of increasing the surface area of the LaNiO₃ perovskite on the catalytic activity were investigated by changing the method of preparing and creating holes in the surface of the samples. Physical and chemical properties of the samples, before and after the reactor test, were determined through ICP, AA, XRD, TGA, TPR, BET, SEM, EDX and TEM techniques. The results of XRD, ICP, AA, SEM, EDX and TEM tests indicated that the citrate sol–gel method is a good way to prepare a homogeneous perovskite LaNiO₃ sample on a scale of nanometers. The results of the TPR test showed using etching in the citrate sol–gel method can produce samples with high stability. The BET results indicated that the surface area of the LaNiO₃ sample tripled with the method suggested in this paper. Changes in preparation method lead to induction time decreasing and temperature increasing. Use of etching in the citrate sol gel method had no significant effect in the results of activity tests versus time reaction at a temperature of 800 °C. TGA curves revealed no production of coke over the process for the produced samples.     

A New Elaboration Route by Sol-Gel Process for Cerium Doped SrHfO3 Films and Powders

We present for the first time the elaboration via sol gel route of cerium (1 mol%) doped SrHfO₃ powders and films. The sol is elaborated using hafnium and strontium ethoxides as precursors and cerium nitrate as dopant. The structure of powders and films are characterized by convergent methods: Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, Raman spectroscopy and optical measurements conducted by the prism coupling method. The powder crystallises from amorphous to pure SrHfO₃ orthorhombic perovskite phase after a 800°C heat treatment. Nevertheless HfO₂ monoclinic phase coexists with orthorhombic perovskite phase after a 1000°C heat treatment. The film is amorphous for annealing temperatures lower than 700°C and presents good waveguiding performances. The film heat-treated at 700°C exhibits a refractive index of 1.810 ± 0.001 (λ = 543.5 nm) for a thickness around 375 nm. The attenuation coefficient obtained on the 400°C heat-treated film is α = 4.0 ± 0.5 dB/cm (λ = 632.8 nm). The film starts to crystallize at 750°C into the SrHfO₃ orthorhombic phase but HfO₂ monoclinic phase is also detected after a heat treatment at 1000°C. The potentiality of sol gel Ce³⁺:SrHfO₃ powders and films for scintillation applications are investigated.     

Sol–gel combustion synthesis of BNBT powders

Ba-modified bismuth sodium titanate with composition 0.94[(Bi_0.5Na_0.5)TiO₃]-0.06BaTiO₃ (BNBT) was prepared by a citrate nitrate sol–gel combustion method. The sol was obtained using barium acetate, bismuth nitrate, sodium nitrate and a peroxo-citrate complex of titanium isopropoxide as starting precursors. Various molar ratios of citrate/nitrate (C/N) were considered for the sol production. The corresponding gels were fired at different temperatures (300, 400, 500 °C) in order to evaluate the conditions necessary to obtain the decomposition of the precursors and the formation of the pure BNBT perovskitic phase in a single step. The best conditions to obtain the desired phase are: (C/N) = 0.2, and combustion temperature of 500 °C. Ball milled powders were densified at a temperature 100 °C lower than the one generally used for powder produced with the conventional mixed oxide route. The electrical properties are comparable to those reported for conventionally prepared materials.     

Attainment of lead titanate

Crystalline PbTiO₃ was obtained through the thermal decomposition of 8-hydroxyquinolinate of lead(II) and that of titanium(IV), which was monitored by TG/DTG/DTA under different atmospheric conditions and with varying heating rates. The compound was prepared from adding 8-hydroxyquinoline solution in the solution of metallic ions Pb(II):Ti(IV) (1:1) under constant stirring at 3°C, having the pH adjusted to 10. The results of these investigations show that different thermal behavior related to the precursor occurred and also the consequent formation of residues which have different crystallinities. No carbonate residues from the thermal decomposition could be determined by XRD and IR. Only PbTiO₃ was observed and confirmed by DSC at 470°C, temperature lower than the tetragonal-cubic transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal decomposition of lead titanyl oxalate tetrahydrate

The thermal behaviour of PbTiO(C₂O₄)₂·4H₂O (PTO) has been investigated, employing TG, quantitative DTA, infrared spectroscopy and (high temperature) X-ray powder diffraction.The decomposition involves four main steps. The first is the dehydration of the tetrahydrate (30–180°C), followed by a small endothermic (270–310°C) and a large exothermic decomposition of the oxalate. The main (exothermic) oxalate decomposition (310–390°C) results in a stable oxide-carbonate PbTiO₂₅.(CO₃)_0.5. In the last step a phase transition, release of CO₂ and ordering of the crystalline cubic PbTiO₃ lattice can be detected (460–530_C).It can be argued that for thermodynamic reasons the presence of lead-oxo- carbonates in the oxide-carbonate intermediate is not possible.No differences could be found in thermal behaviour of two crystallographically different synthetic forms of PTO, of which one has an orthorhombic lattice.     

Lead-Doped Titanium-Oxo Clusters as Molecular Models of Perovskite-Type PbTiO3 and Electron-Transport Material in Solar Cells

In this work we have successfully prepared two lead-doped titanium-oxo clusters with core structures that resemble isolated perovskite PbTiO₃ species. In the obtained highly symmetric Pb₈Ti₇-oxo cluster, the central TiO₆ octahedra are orthogonally extended to adjacent octahedra through corner-sharing and the eight dopant lead ions form a cubic arrangement, making it the first molecular model of perovskite PbTiO₃. Moreover, the clusters readily dissolved in chloroform and showed high solution stability, as confirmed by MALDI-TOF MS measurements. Based on such solution processability, they can be easily spin-coated to form homogeneous films, which were employed as electron-transport materials in perovskite solar cells to give an average power conversion efficiency of around 15 % and improved device stability. This newly developed bottom-up cluster assembly method provides an efficient approach to the construction of atomically precise models of perovskite metal oxides as well as potential molecular tools to extend their applications.     

Sol–gel synthesis,optical and structural characterization of ZrOS nanopowder

In this paper, we report the synthesis of tetragonal zirconium oxysulfide t-ZrOS nanopowder by the sol–gel method using water solution of a precursor containing thiourea [CS(NH₂)₂] and zirconium in the form of an anionic oxalate complex [Zr(C₂O₄)]^4?. The tetragonal t-ZrOS structure with space group P4/nmm revealed by X-ray patterns showed preferred orientation along (101) plane. For surface morphology, compositional and optical absorption studies, scanning electron microscopy, energy dispersive X-ray and ultraviolet–visible spectroscopy were employed for characterization of the powder respectively. A nearly constant value of the refractive index at higher wavelength λ ≥ 1,100 nm was found to be 2.19. High indirect and direct optical band gap of ~2.0 and 2.50 eV with absorbance <40 % were obtained for the powder.