Lithium-Ion conducting oxides: Synthesis,structure, and electroconducting properties

The properties of perovskite type ABO₃ lithium-ion conducting oxides based on lanthanum lithium titanate (La,Li)TiO₃, lanthanum lithium niobate and tantalate, and Li₅La₃M₂O₁₂ (M = Nb, Ta) garnets were considered. Approaches to modification of the properties of these oxides, as well as the charge-compensation mechanisms associated with nonisovalent doping were discussed. Special consideration was given to phase formation and crystal structure in relation to the composition and preparation conditions of the oxides.     

Low temperature nanostructured lithium titanates: controlling the phase composition, crystal structure and surface area

Low temperature lithium titanate compounds (i.e., Li₄Ti₅O₁₂ and Li₂TiO₃) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m²/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.     

Hydrothermally assisted complex polymerization method for barium strontium titanate powder synthesis

Barium strontium titanate was obtained by hydrothermal treatment of barium strontium titanate citric precursor solution, previously prepared by complex polymerization method. The thermally induced phase evolution was followed at various temperatures up to 800 °C using thermogravimetric and differential thermal analysis, X-ray diffraction analysis, and Raman spectroscopy. Microstructural characterization of barium strontium titanate powders was performed by scanning and transmission electron microscopy. The proposed synthesis route has been proven as a better and faster method for barium strontium titanate powder preparation as compared to the conventional complex polymerization route. The method was found efficient for production of low agglomerated, fine, nanosized barium strontium titanate powder with well defined stoichiometry, and sub-micron particle size. The results of structural and microstructural characterization showed the complete crystallization of carbonate-free barium strontium titanate powder at 700 °C with an average size of crystallites below 50 nm.     

A novel route to perovskite lead titanate from lead and titanium glycolates via the sol–gel process

Pure perovskite lead titanate powder (PbTiO₃) is successfully produced via the sol–gel process using lead and titanium glycolates as starting precursors and has been synthesized by the oxide one spot synthesis process. The obtained lead titanate is of the tetragonal form of the perovskite phase, with high purity and nearly zero moisture content. From high‐resolution mass spectra, the XRD technique, Raman‐FTIR and TGA‐DTA analysis, the lead–titanium glycolates undergo sol–gel transition through the formation of Pb? O? Ti bonds. From the SEM micrographs, the PbTiO₃ particle shape transforms from an agglomerate sphere to a needle and fiber‐like shapes as the calcination temperature is varied above T_c. The corresponding molecular structural transformation, from the tetragonal form to the cubic form, occurs at 430 °C. The lead titanate powder calcined at 300 °C for 3 h has the highest dielectric constant and electrical conductivity values, namely 17470 and 1.83 × 10^?3, respectively. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of highly pure nanocrystalline and mesoporous CaTiO3 by a particulate sol–gel route at the low temperature

The low temperature perovskite-type calcium titanate (CaTiO₃) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution about 17 nm. X-ray diffraction and Fourier transform infrared spectroscopy revealed that, the synthesized powders had highly pure and crystallized CaTiO₃ structure with preferable orientation growth along (1 2 1) direction at 400–800 °C. The activation energy of crystal growth was calculated 5.73 kJ/mol. Furthermore, transmission electron microscope images showed that the average crystallite size of the powders annealed at 400 °C was around 3.5 nm. Field emission scanning electron microscope analysis and atomic force microscope images revealed that, the deposited thin films had uniform, mesoporous and nanocrystalline structure with the average grain size in the range 33–39 nm depending on annealing temperature. Based on Brunauer–Emmett–Teller (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 51–21 m²/g at 400–800 °C. One of the smallest crystallite size and one of the highest surface areas reported in the literature is obtained which can be used in many applications, such as photocatalysts.     

铌酸锂、钽酸锂晶体的结构特征

从铌酸锂和钽酸锂晶体的结晶学数据出发,分析其结构特征和组成化学键的结合情况.对于这两个晶体的结晶学格位占有情况和阳离子的位移进行了理论上的分析.作者首次明确地给出了铌酸锂和钽酸锂晶体中与晶体组成有关的阳离子位移趋势.     

Nano Silicon from Nano Silica Using Natural Resource (Rha) for Solar Cell Fabrication

Abstract

High purity (～99%) nano silica with an average particle size of ～100 nm was extracted at pH 3 at 650°C from a natural resource, rice husk, using alkaline extraction followed by acid precipitation method. Using nano silica as a precursor, silicon (Si) nanoparticles have been synthesized by high-temperature magnesiothermic reduction method. The prepared sample was characterized by X-ray diffraction, particle size analyzer, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray fluorescence analyzer, and UV–Vis spectroscopy. The comprehensive characterization studies indicate the pure phase formation of Si and the variation of particle size from 70 nm to 100 nm for samples synthesized at different sintering temperatures. Moreover, the silicon nanoparticles produced at 850°C have pure phase formation, high purity, and good absorption peaks. The efficiency calculated through IV characteristics is found to be increasing in silicon and ruthenium combination (2.67%), which is better than that achieved from the conventional solar cells. The produced silicon nanoparticles could be applied as an anode material for solar cell fabrication.     

Effect of sol-gel preparation method on particle morphology in pure and nanocomposite PZT thin films

Double-scale composite lead zirconate titanate Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films of 360 nm thickness were prepared by a modified composite sol-gel method. PZT films were deposited from both the pure sol and the composite suspension on Pt/Al₂O₃ substrates by the spin-coating method and were sintered at 650°C. The composite suspension formed after ultrasonic mixing of the PZT nanopowder and PZT sol at the powder/sol mass concentration 0.5 g mL⁻¹. PZT nanopowder (≈ 40–70 nm) was prepared using the conventional sol-gel method and calcination at 500°C. Pure PZT sol was prepared by a modified sol-gel method using a propan-1-ol/propane-1,2-diol mixture as a stabilizing solution. X-ray diffraction (XRD) analysis indicated that the thin films possess a single perovskite phase after their sintering at 650°C. The results of scanning electron microscope (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses confirmed that the roughness of double-scale composite PZT films (≈ 17 nm) was significantly lower than that of PZT films prepared from pure sol (≈ 40 nm). The composite film consisted of nanosized PZT powder uniformly dispersed in the PZT matrix. In the surface micrograph of the film derived from sol, large round perovskite particles (≈ 100 nm) composed of small spherical individual nanoparticles (≈ 60 nm) were observed. The composite PZT film had a higher crystallinity degree and smoother surface morphology with necklace clusters of nanopowder particles in the sol-gel matrix compared to the pure PZT film. Microstructure of the composite PZT film can be characterized by a bimodal particle size distribution containing spherical perovskite particles from added PZT nanopowder and round perovskite particles from the sol-matrix, (≈ 30–50 nm and ≈ 100–120 nm), respectively. Effect of the PZT film preparation method on the morphology of pure and composite PZT thin films deposited on Pt/Al₂O₃ substrates was evaluated.     

Characterization of metal oxide-doped lutetium orthoferrite powders from the pigmentary point of view

This thesis deals with the preparation and characterization of inorganic pigments based on perovskite structure of metal oxide-doped LuFeO₃. Powder samples were prepared by the conventional ceramic method, i.e., solid-state reaction. Heating temperature was chosen according to results of TG/DTA. Prepared pigments were incorporated into an organic binder system, and their color properties were evaluated by measuring the reflectance in the visible region of light. The most interesting color properties were obtained by preparation of sample Lu_0.98Ca_0.02FeO_3?δ with mineralizer LiF at the temperature 900 °C. Mean size of its particles is 4 μm. X-ray diffraction analysis confirmed a single-phase orthorhombic structure with lattice parameters a = 0.521310 nm, b = 0.55535 nm, and c = 0.75626 nm. Thermal stability of the sample is limited by the temperature of 1,150 °C. Further, the effectiveness of other metal oxide (CoO-, ZnO-, Bi₂O₃-, and Sb₂O₃)-doped Lu_0.98Ca_0.02FeO_3?δ system was evaluated with respect to their phase composition, thermal stability, particle size distribution, and color properties. The conclusions of the research showed that a sample containing antimony oxide is the mixture with the best pigmentary-application properties. The powder has a clear orange color, high thermal stability up to 1,340 °C, and mean particle size 4 μm.     

Liquid-phase synthesis of barium acetatotitanyl and barium oxalatotitanyl as intermediates for preparing nanosized barium titanate

Liquid-phase methods (an oxalate process in aqueous solution and a semialkoxide sol-gel process in anhydrous acetic acid) were used to prepare barium acetatotitanyl (BAT) and barium oxalatotitanyl (BOT), which are potential fillers for electrorheological liquids, and to prepare barium titanate during heat treatment of the aforementioned intermediates at 1200°C. The materials were characterized using electron microscopy, FTIR spectroscopy, and thermal analysis. The particle size was 80 to 100 nm for BAT powders and 20 to 50 nm for BOT powders. X-ray spectra of the powders dried at 120°C contain reflections from a barium titanate phase. The dielectric spectra of the materials synthesized were studied for suspensions in PMS-20 silicone oil over the frequency range from 25 to 10⁶ Hz up to 4 kV/mm. The dielectric parameters of BOT suspensions decrease hyperbolically with rising alternate current frequency, whereas BAT suspensions give rise to a relaxation dielectric spectrum with relaxation times on the order of 10⁻³ s.     

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.     

Synchrotron radiation study of silver and chromium particles supported on graphite

Silver and chromium particles in the size range 10 nm to 25 nm formed by deposition in ultra-high vacuum on graphite have been studied using synchrotron radiation. We have determined the island size by measuring the spectral dependence of the reflectivity of each sample using light in the photon energy range 35 eV to 190 eV. Comparing this measurement to a calculation of the reflectivity modified by the size-dependent extinction, determined using Mie theory, gives the average particle radius. Using this sizing technique we find that, for the growth of silver at room temperature, the average radius increases linearly with the cube root of evaporation time. Deposition with the substrate at elevated temperatures produces, for similar coverages, an increase in the average size for temperatures between 200°C and 225°C followed by a rapid decrease above 225°C. Chromium shows size effects in the photoemission spectra from the 3s and 3p core levels and the 3d valence band. With decreasing radius a decrease in the multiplet splitting of the 3s core level and a large change in the relative intensity among the 3p multiplets occurs indicating increased electron correlation as the system becomes smaller. A narrowing of the valence band also occurs which we attribute to a structural change at the surface of the particles.     

Tetrahydrofuran Activation Assisted Synthesis of Nanosized Lithium Niobate and Lithium Tantalate

Black solid precursors obtained from reactions between MCl₅ (M = Nb, Ta) and alkyllithiums, n‐butyllithium (ⁿBuLi) and ethyllithium (EtLi), in tetrahydrofuran (THF) were heat treated under vacuum at 673–973 K to form nano‐sized particles (20–100 nm in diameter) of lithium niobate (LiNbO₃) and lithium tantalate (LiTaO₃). Stoichiometry of the reactants is critical and affects the phases of the products. Based on the volatile byproducts detected, a reaction pathway involving the activation of THF by alkyllithiums is proposed to be important for the formation of LiNbO₃ and LiTaO₃ precursors.     

Nanosized bismuth titanate (Bi4Ti3O12) system drive through auto-combustion process by using suspension titania (TiO2)

Bismuth titanate (Bi₄Ti₃O₁₂) was developed by means of titanium oxide (TiO₂) suspension in auto-combustion process at 220 °C to get nanosized (20 ± 5 nm) bismuth titanate (Bi₄Ti₃O₁₂) powder. Complete piezoelectric phase (tetragonal) was obtained after calcination at 700 °C. Dilatometery of compacts was performed to find out sintering temperature. On the basis of shrinkage results, compacts were sintered at 750, 800, and 850 °C for 2 h. After sintering single phase was obtained with orthorhombic structure analyzed by X-ray diffraction and also investigated by Rietveld method. High-resolution scanning electron microscopy revealed that fine plate-like structure which is a characteristic of BIT powder can be obtained at 850 °C. Sintering results indicate that density and average grain size increase with the increasing temperature. A maximum of about 90 % of the theoretical density was achieved for the sintered product at 850 °C.     

Thermal, structural, magnetic and photoluminescence studies on cobalt ferrite nanoparticles obtained by citrate precursor method

Magnetic nanoparticles of cobalt ferrite have been synthesized by citrate precursor method. TG-DSC studies have been made to get the idea of the optimum temperature of annealing that could lead to the formation of nanoparticles. Annealing the citrate precursor was done at 450, 650, and 973?°C. The X-ray diffraction (XRD) studies and the scanning electron microscopy (SEM) have been used for characterization. The data from vibrating sample magnetometer and photoluminescence spectrometer (PL) have been analyzed for exploring their applications. Using the Scherrer formula, the crystallite size was found to be 25, 32, and 43?nm, respectively, using the three temperatures. The particle size increased with annealing temperature. Rietveld refinements on the X-ray (XRD) data were done on the cobalt ferrite nanoparticles (monoclinic cells) obtained on annealing at 650?°C, selecting the space group P2/M. The values of coercivity (1574.4?G) and retentivity (18.705?emu g^?1) were found out in the sample annealed at 650?°C while magnetization (39.032?emu g^?1) was also found in the sample annealed at 973?°C. The photoluminescence (PL) property of these samples were studied using 225, 330, and 350?nm excitation wavelength radiation source. The PL intensity was found to be increasing with the particle size.     

Studies of dielectric characteristics of BaBi2Nb2O9 ferroelectrics prepared by chemical precursor decomposition method

BaBiNb₂O₉ (BBN) powders in the nanometer range were prepared by chemical precursor decomposition method (CPD). TG–DTA showed that precursor sample got freed from organic contaminants at 575 °C. XRD showed that a single phase with the layered perovskite structure of BBN was formed after calcining at 600 °C. No intermediate phase was found during heat treatment at and above 600 °C. The crystallite size (D) and the effective strain (η) were found to be 26 nm and 0.000867, respectively, while the particle size obtained from TEM was 28 ± 2 nm. SEM revealed that the average grain size after sintering at 900 °C for 4 h was ∼1.67 μm. A relative density of ∼93% was obtained using a two-step sintering process at moderate pressure. Dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C and frequencies from 1 kHz to 5 MHz. Strong dispersion of the complex relative dielectric constant was observed including typical relaxor features such as shift of permittivity maximum with frequency and broadening of the peak maximum. The high dielectric constant of 545 measured at 100 kHz and other properties of BBN ceramics were compared to that of BBN prepared by other conventional methods and found to be superior.     

How synthesis parameters influence the quality of lead magnesioniobate PbMg1/3Nb2/3O3

Lead magnesioniobate PbMg_1/3Nb_2/3O₃ (PMN) has been prepared using lead oxide and magnesium niobate. Factors that influence the perovskite/pyrochlore ratio in the PMN structure have been studied. In order for the maximal amount of the perovskite phase to be obtained, synthesis should be carried out at 850?C900°C; an excess of MgO (1?C5 wt %) does not exert a positive effect. An excess of PbO (5?C7 wt %) allows one to obtain a phase that contains 85% PMN, with the perovskite structure. The perovskite lattice is found to be stabilized as a result of cationic substitutions (Yb, Lu) in the Mg-Nb sublattice due to the formation of solid solution Pb(Mg_1/3Nb_2/3)_{1 ? x} Yb(Lu) _x O₃, where 0 ?? x ?? 0.9.     

Preparation and microstructure of sol-gel derived silver-doped silica

Silver-doped silica was prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) in the presence of a silver nitrate (AgNO₃) solution by two different synthesis methods. In the first synthesis route, sol-gel mixtures were prepared using an acid catalyst. In the second synthesis route, silver-doped silica gels were formed by two-step acid/base catalysis. For the same concentration of silver dopant [AgNO₃]/[TEOS] = 0.015 acid-catalyzed sol-gel formed a microporous silica with an average pore size of <25 Å whereas the two-step catalyzed silica had an average pore size of 250 Å and exhibited a mesoporous structure when fully dried. The differences in the pore size affected the silver particle formation mechanism and post-calcination silver particle size. After calcination at 800 °C for 2 h the acid-catalyzed silica contained metallic silver particles size with an average particle size of 24 ± 2 nm whereas two-step catalyzed silica with the same concentration of [AgNO₃]/[TEOS] = 0.015 contained silver nanoparticles with an average size of approximately 32 ± 2 nm. Mechanisms for silver particle formation and for silica matrix crystallization with respect to the processing route and calcination temperature are discussed.     

Synthesis and characterization of SmAlO<Subscript>3</Subscript> dielectric material by citrate precursor method

SmAlO₃ nanopowder synthesized by a citrate precursor method using citric acid as a chelating agent and ethylene glycol as an esterifying agent was reported in this paper. The phase purity of the as-prepared powder was examined using thermogravimetry (TG) analysis and differential scanning calorimetry (DSC) analysis, Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction (XRD) studies showed that pure SmAlO₃ phase with orthorhombic perovskite structure could be synthesized at 800 °C for 2 h without any detectable intermediate phase. The average particle size calculated from transmission electron microscopy (TEM) investigation for the powder synthesized at 900 °C was as low as 45 nm. The nanopowder was sintered to a density of 97% of the theoretical density at 1,550 °C for 2 h and the bulk ceramics exhibited excellent microwave dielectric properties as follows: a dielectric constant of 20.54, a quality factor of 75,380 GHz and a temperature coefficient of resonate frequency of −69.2 ppm/K.     

Thermoresponsive submicron-sized core–shell hydrogel particles with encapsulated olive oil

Thermoresponsive submicron-sized core–shell hydrogel particles with incorporated olive oil were synthesised and studied. The microspheres having poly(N-isopropylacrylamide-co-methyl methacrylate) core and poly(N-isopropylacrylamide) shell were synthesised by emulsifier-free seed polymerisation method. The morphology, particle size and distribution characteristics of the core microspheres were studied with different amount of initiator, monomer–solvent ratio and polymerisation time using scanning electron microscopy and dynamic light scattering particle size analysis. The prepared core and core–shell microspheres were regularly spherical with average size of around 190.0 and 320.0 nm respectively and nearly monodispersed size distribution. Transmission electron microscopy study revealed the core–shell structure of the microspheres. The thermoresponsive transition temperature (T _t) of the core–shell microspheres was determined as 33 °C by optical absorbance measurement, dynamic light scattering particle size analysis and differential scanning calorimetry. The release rate of olive oil from core–shell microspheres was accelerated by squeezing out the entrapped olive oil as the temperature was increased above T _t. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy study indicated the formation of copolymer.