Preparation of nanosized LaCoO3 perovskite oxide using amorphous heteronuclear complex as a precursor at low temperature

Nanosized LaCoO₃ cobaltite oxide powder with perovskite structure was successfully synthesized at a relatively low calcination temperature using an amorphous heteronuclear complex, LaCo(DTPA)·6H₂O, as a precursor. The precursor decomposed completely into cobaltite oxide above 400 °C according to the DTA and TGA results. XPS revealed that the decomposed species was composed of LaCoO₃ cobaltite oxide after the precursor was calcined at 500 °C for 2 hours. XRD demonstrated that nanosized LaCoO₃ crystalline powder with perovskite structure was formed after the calcination temperature increased to 600 °C. The grain size and the crystal size of LaCoO₃ increased with the calcination temperature from 500 °C to 800 °C, and the heat-treatment time has a less obvious effect on the grain size and the crystal size. It is a useful way to synthesize nanosized perovskite oxides using an amorphous complex as a precursor. This method can be easily quantitatively controlled.     

Preparation of nanosized Gd2CuO4 cuprate using amorphous heteronuclear complex as a precursor at low temperature

Nanosized Gd₂CuO₄ cuprate oxide was prepared at a low temperature using an amorphous heteronuclear complex, Gd₂Cu(DTPA)_1.6·6H₂O, as a precursor. DTA and TGA indicated that the precursor can be completely decomposed above 500°C. XPS indicated the decomposition product consisted of Gd₂CuO₄ cuprate oxide after the precursor was calcined at 500°C for 2 h. XRD demonstrated that the nanosized crystalline Gd₂CuO₄ cuprate was formed after the calcination temperature increased to 600°C. TEM showed that the particle size of Gd₂CuO₄ cuprate increased from 20 to 50 nm when the calcination temperature increased from 500 to 800°C, and the particle size increased from 10 to 30 nm when the precursor was calcined at 500°C from 1 to 8 h.     

Preparation and conducting performance of LaNiO3 thin film on Si substrate

LaNiO₃ thin film with perovskite structure was successfully prepared on Si (111) substrate via an amorphous heteronuclear complex as precursor. The annealing temperature had a significant effect on the crystallization of LaNiO₃ film. The crystallization temperature of the film was higher than that of the powder samples due to the interface reaction between the layer and the substrate. The thickness of LaNiO₃ thin film increased with the precursor concentration and the texture of the film could be improved significantly by adding some polyethylene glycol (PEG) as additive. A remarkable decline of the electrical resistivity was observed when the calcination temperature was raised to 800 °C. The conductivity of LaNiO₃ film increased gradually when the temperature decreased and the film showed a metallic behavior.     

LaFeO3 perovskite-type oxide prepared by oxide-mixing, co-precipitation and complex synthesis methods

The perovskite oxide, LaFeO₃, was synthesized by three different preparation methods i.e., the calcination of a mixture of La₂O₃ and Fe₂O₃ (La-Fe-O), a co-precipitated precursor (La-Fe-OH), La(OH)₃ and Fe(OH)₃, and a heteronuclear complex (La-Fe-CN), La[Fe(CN)₆] · 5H₂O. The obtained powders were characterized by thermogravimetric analysis, powder X-ray diffraction, electron microprobe analysis, specific surface area measurement and scanning electron microscopy. The formation of LaFeO₃ is clearly recognized for La-Fe-O, La-Fe-OH and La-Fe-CN at calcining temperatures above 1000, 800 and 600°C, respectively. The mean particle diameter of La-Fe-CN calcined at 600°C for 2 hours was 30 nm. The LaFeO₃ perovskite oxide powder obtained by the thermal decomposition of La-Fe-CN was most uniform on an atomic level and the nanosized LaFeO₃ powder was obtained at low temperatures. Furthermore, the sinterability was good.     

Low temperature synthesis of perovskite oxide using the adsorption properties of cellulose

La_0.8Sr_0.2CoO₃ (LSCO) oxide powder was prepared using the adsorption properties of cellulose. The preparation process was studied by XRD, FTIR, TG-DTA and CO₂-TPD techniques. The results of XRD, IR and TG-DTA testified that cellulose could successfully reserve the homogeneity of the solution system to the solid precursor. During the early stage of pyrolysis, cellulose was partially oxidized, and some COO^– groups appeared in its texture, which were then complexed with the adsorbed metal ions, and effectively suppressed the aggregation of metal ions. Formation of a pure perovskite and the properties of the powder resulted were found to be significantly influenced by the cellulose to metal nitrate ratio. Also the properties of the resulting powder were greatly influenced by the calcination conditions. If the produced carbon dioxide could not be eluted in time, carbonate would be formed in the bulk. Hence, a high calcination temperature (>800°C) was needed to acquire a pure phase LSCO. At optimized conditions, nano-crystal LSCO could be obtained at as low as 500°C.     

Perovskite phase formation in the PbMg1/3Nb2/3 O3-PbZrO3-PbTiO3 system by the columbite route

The reaction mechanism of PbMg_1/3Nb_2/3O₃-PbZrO₃-PbTiO₃ (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 °C. The effects of heating and cooling rate during the calcination of 3PbO +MgNb₂O₆+PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-0.1 PZTsolid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 °C for 2 H. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps: (i) decomposition of columbite (MgNb₂O₆) by reacting with PbO at 350 to 600 °C (ii) the formation of a B-site-deficient pyrochlore phase Pb₂Nb_1.33Mg_0.17O_5.50 at close to 650 °C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb₂Nb_1.33Mg_0.17O_5.50 pyrochlore phase with MgO and PZT above 650 °C.     

Synthesis of nanosized β-BiTaO4 by the polymeric precursor method

β-BiTaO₄ powder was synthesized by the citrate method, using bismuth citrate and TaCl₅ as precursors. The citrate gel was characterized by thermal analyses (TG and DTA), in order to determine the best polymerization temperature. The polymeric precursor is essentially amorphous and after calcination at 400 °C a mixture of tantalates, that are isomorphic to Bi₃NbO₇ and Bi₅Nb₃O₁₅, starts to crystallize. At 600 °C, in addition to those phases, one could observe some peaks related to β-BiTaO₄. Finally, at 800 °C β-BiTaO₄ can be observed as a pure phase, with particle size estimated as 47 nm. The precursor polymeric method allowed obtaining β-BiTaO₄ pure phase at temperatures significantly lower than those found for solid state reaction method.     

Capacity fading of LiMn2O4 electrode: Influence of calcination temperature

Spinel-type Li-Mn oxides of formula LiMn_2–x O₄ were prepared by the Pechini method in the range of 600–850°C for 4 h. These spinels were investigated by X-ray powder diffraction, SEM (scanning electron microscope), ICP, chemical titration and galvanostatic cycling at 0.2C rates. The effect of calcination temperature is evaluated. With increasing calcination temperature, Mn valence-state of the powder decreased while size of powder increased. The cycle life of the powder decreases with increasing calcination temperature. The results indicated that the Mn valence-state and powder size of cathode powder should be important variables to improve cycle life. The effect of cell polarization effect on the cycle life is also discussed.     

Preparation of SrTiO3 nanoparticles by the combination of solid phase grinding and low temperature calcining

Spherical SrTiO₃ nanoparticles with diameters of 15-35 nm were successfully synthesized by a solid phase grinding followed by low-temperature (400-600 °C) calcination method, using strontium hydroxide and tetrabutyl titanate as reactants. The as-synthesized samples were characterized by XRD, FT-IR, SEM and TEM, and the formation process of the products was investigated by means of TG-DTA. The results show that the as-synthesized SrTiO₃ nanoparticles with uniform sizes belong to cubic perovskite structure. The crystallite size and crystallinity increase with the increasing of calcination temperature. In the meantime, the crystal water contained in the reactant of strontium hydroxide also affects the crystallinity of products.     

New preparation method of low-temperature sinterable Pb(Mg1/3Nb2/3)O3 powder and its dielectric properties

A relaxor ferroelectric material, Pb(Mg_1/3Nb_2/3)O₃(PMN) with perovskite phase was prepared by one-step calcination in the present study. The PMN powder with >99% perovskite phase was prepared successfully by adding an aqueous Mg(NO₃)₂ solution rather than MgO to the alcoholic slurry of PbO and Nb₂O₅, followed by calcination at 950°C for 2 h. The DSC and XRD analysis showed that the pathway in the one-step calcination was different from those of the known columbite or solution processes. The PMN powder sintered to 95.6% of the theoretical density at even 900°C for 2 h. Its room temperature dielectric constant showed 13800 at 1 kHz, the loss of dielectric constant of 0.05% and the specific resistivity of 2.4 × 10¹⁰ ·cm.     

Preparation of LaNiO3 powder from coprecipitated lanthanum-nickel oxalates

Coprecipitation of lanthanum and nickel oxalates in a water-alcohol mixed solution of an oxalic acid resulted in a simultaneous and homogeneous deposition of the respective oxalate particles with a desired cation ratio. The coprecipitated oxalate could be readily converted to a fine powder (5 to 6 m² g^–1) of the desired LaNiO₃ by heating at 800 to 850° C. Detailed examination of some precipitation conditions established an optimum procedure needed for the powder synthesis of LaNiO₃. Thermal analysis showed that La₂NiO₄ (high temperature form) is transiently produced prior to the formation of LaNiO₃. Mixed valency of the nickel ion in the synthesized powders was quantitatively determined by means of the oxidation-reduction titration, suggesting that the chemical formula of the powders might be LaNiO_{2.85 to 2.90}.     

Structural properties of Al2O3-La2O3 binary oxides prepared by sol-gel

The structural properties of La₂O₃ and Al₂O₃-La₂O₃ binary oxides prepared by sol-gel were studied by XRD, HRTEM and UV-vis. The binary oxides with high lanthana contents show an amorphous structure after calcination at 650 °C. At calcination temperatures higher than 1000 °C there is a phase transformation from the amorphous state to the crystalline LaAlO₃ with a perovskite structure. The structure of La₂O₃ is consistent with the hexagonal system; however, some crystalline microdomains with a monoclinic structure were detected by HRTEM. Islands of La₂O₃ and LaAl₁₁O₁₈ phases were detected at high lanthana concentration in the binary oxide. The modification in the coordination shell of the Al³⁺ cations due to the interaction with La³⁺ cations confirms the formation of phases with a perovskite structure and the presence of islands of the LaAl₁₁O₁₈ phase.     

Formation of SrTiO3 from Sr-oxalate and TiO2

SrTiO₃ powder has been prepared from Sr-oxalate and TiO₂ precursors, instead of using titanyl-oxalate. Sr-oxalate was precipitated from nitrate solution onto the surface of suspended TiO₂ powders. Crystallization of SrTiO₃ from the precursor was investigated by TGA, DTA and XRD analysis. It is evident that precursor, upon heating, dehydrates in two stages, may be due to the presence of two different types of Sr-oxalate hydrates. Dehydrated precursor then decomposes into SrCO₃ and TiO₂ mixture. Decomposition of SrCO₃ and simultaneous SrTiO₃ formation occur at much lower temperature, from 800 °C onwards, due to the fine particle size of the SrCO₃ and presence of acidic TiO₂ in the mixture. The precursor completely transforms into SrTiO₃ at 1100 °C. About 90 nm size SrTiO₃ crystallites are produced at 1100 °C/1 h, due to the lower calcination temperature and better homogeneity of the precursor.     

Nano-sized CeO2 with extra-high surface area and its activity for CO oxidation

Using Cerium chloride octahydrate as a precursor and dodecyl sodium sulfate as a template, nano-sized CeO₂ with extra-high surface area were synthesized by a surfactant-templated method. The highest surface area of the synthesized CeO₂ was 457 m² g⁻¹. Combined with XRD, TEM and BET results, it was found that when the calcination temperature was lower than 600 °C, the particle size of CeO₂ hardly changed while the surface area declined due to the co-action of the sintering and agglomeration of the particles. However, with a high calcination temperature (above 600 °C), the sintering was the mainly reason to the decline of the BET surface area and the rapid growth of the particles size. Moreover, by the test for CO oxidation, it was found that the reactivity of the CeO₂ sample remarkably increased with decreasing particle size, which was due to the fact that smaller particles provided more structural defects.     

Vapor-phase synthesis of a solid precursor for α-alumina through a catalytic decomposition of aluminum triisopropoxide

A new solid precursor, hydrous aluminum oxide, for α-alumina nanoparticles was prepared by thermal decomposition of aluminum triisopropoxide (ATI) vapor in a 500 mL batch reactor at 170-250 °C with HCl as catalyst. The conversion of ATI increased with increasing temperature and catalyst content; it was nearly complete at 250 °C with the catalyst at 10 mol% of the ATI. The obtained precursor particles were amorphous, spherical and loosely agglomerated. The primary particle size is in the range 50-150 nm. The ignition loss of the precursor was 24%, considerably lower than 35% of Al(OH)₃, the popular precursor for alumina particles. Upon calcination of the precursor at 1200 °C in the air with a heating rate of 10 °C/min and a holding time of 2 h, the phase was completely transformed into α. The spherical particles composing the precursor turned worm-like by the calcination probably due to sintering between neighboring particles. The surface area equivalent diameter of the resulting α-alumina was 75 nm.     

Synthesis of zinc oxide/silica composite nanoparticles by flame spray pyrolysis

Zinc oxide (ZnO)/silica (SiO₂) composite nanoparticles were made by flame spray pyrolysis. The effects of the Zn/Si ratio on particle properties were examined and compared with those of the pure ZnO and SiO₂ particles made at the same conditions. Polyhedral aggregates of nano-sized primary particles were obtained in all experiments. The mixed-oxide primary particle size was smaller than that of pure oxides. The primary particles consisted of ZnO nano-crystals and amorphous SiO₂, as seen by high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) analysis using the fundamental parameter approach. The XRD size of ZnO was controlled from 1.2 to 11.3 nm by the initial precursor composition and it was consistent with HR-TEM. The composite particles exhibited an excellent thermal stability and little crystalline growth of ZnO (e.g., from 1.9 to 2.2 nm) was observed even after calcination at 600°C.     

Evaluation and characterization of nanostructure hydroxyapatite powder prepared by simple sol-gel method

Many attempts have been focused on preparing of synthetic hydroxyapatite (HA), which closely resembles bone apatite and exhibits excellent osteoconductivity. Low temperature formation and fusion of the apatite crystals have been the main contributions of the sol-gel process in comparison with conventional methods for HA powder synthesis. This paper describes the synthesis of nano-HA particles via a sol-gel method. Nanocrystalline powder of hydroxyapatite (HA) was prepared using Ca(NO₃)₂·4H₂O and P₂O₅ by a simple sol-gel approach. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for characterization and evaluation of the phase composition, morphology and particle size of products. The presence of amorphous and crystalline phases in the as-dried gel precursor was confirmed by the evaluating technique. Single phase of HA was also identified in the heat treated powder by XRD patterns. SEM and TEM evaluations showed that the obtained powder after heat treatment at 600 °C was agglomerated and composed of nanocrystalline (25-28 nm) HA particles. Increasing the sintering temperature and time could cause decomposition of HA into β-tricalcium phosphate and calcium oxide. The prepared nanocrystalline HA is able to improve the contact reaction and the stability at the artificial/natural bone interface for medical applications.     

Fabrication of polycrystalline lanthanum manganite (LaMnO3) nanofibers by electrospinning

Lanthanum manganite (LaMnO₃) nanofibers were successfully fabricated by electrospinning utilizing sol-gel precursors. Polycrystalline cubic-perovskite structure LaMnO₃ fibers of 50-100 nm were obtained by calcination of the inorganic/organic hybrid fibers at 600 °C for 1 h. The XRD results showed that the grain size of the fibers increased significantly with the increase of calcinations temperature. The average diameter of crystal grains was 17 nm after calcined at 400 °C for 2 h, then grew to 20 nm after heated up to 600 °C for 1 h. The morphology, microstructure, crystal structure and thermal analysis were investigated by SEM, TEM, XRD and TG-DSC, respectively.     

The low temperature synthesis and characterization of Bi3.25La0.75Ti3O12 powder by hydroxide coprecipitation in aqueous medium

The fine powders of Bi_3.25La_0.75Ti₃O₁₂ (BLT) were prepared by coprecipitaton method in aqueous medium at low temperature. The differential thermal analysis (DTA), thermo-gravimetric analysis (TG) and X-ray diffraction (XRD) were employed to evaluate the phase formation of BLT and TEM was used to characterize and observe the particle size and morphology of BLT powder obtained. The results show that the bismuth layer perovskite phase of BLT can begin to form at as low as 500 °C by the coprecipitation method. When the precipitates obtained were calcined at 600 °C for 2 h, the mono-phase and perfect BLT powder was synthesized. The BLT powder obtained consists of irregular or plate-like particles which are less than about 100 nm and is nearly aggregate free.     

Microstructure characterization of sol-gel derived PZT films

The crystallization of sol-gel derived amorphous PZT films deposited on a MgO single-crystal substrate and a SiO₂ glass substrate was examined. The pyrochlore crystallites, 5 nm in size, were homogeneously nucleated in the amorphous films at 350 °C. The nucleation temperature of pyrochlore did not depend on the type of substrate. Fine pyrochlore grains were stable even during annealing at high temperatures up to 600 °C. The perovskite formation temperature was dependent on the substrate, and was about 550 °C on the MgO single-crystal substrate and about 750 °C on the SiO₂ glass substrate. The perovskite was heterogeneously nucleated preferentially at the substrate-film interface. Perovskite nucleation was more difficult at the SiO₂ glass-film interface than at the MgO single crystal-film interface. The ease of nucleation reflected the perovskite formation temperature. Perovskite crystals grew fairly rapidly, once they were nucleated in the films. In the multiple-coated films, the interface between successive layers of PZT films was a favourable nucleation site of perovskite, and the columnar perovskite grains passing through the interface were often developed.