Synthesis of Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramic scintillators by the polymeric precursor method

Bismuth germanate ceramic powders were synthesized for the first time by the polymeric precursor method (Pechini’s method). Differential thermal analysis and thermogravimetric techniques were used to study the decomposition of the resin precursor, which indicated a suitable calcination temperature at 600 °C. It was observed that the mass loss occurs in two main stages that are associated with two exothermic reactions. The crystalline phases of the powders were inspected by the X-ray diffraction technique after thermal treatment between 300 and 600 °C. Single phase Bi₄Ge₃O₁₂ ceramic bodies were obtained after sintering at 840 °C for 10 h. The sintered ceramics presented a luminescence band emission centred at around 530 nm when excited with X-rays and UV radiation.     

Bi1.5ZnNb1.5O7 cubic pyrochlore ceramics prepared by aqueous solution–gel method

Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramic was successfully prepared by the aqueous solution method. The preparation, microstructure development and dielectric properties of ceramics were investigated. Homogeneous precalcined ceramics powders have a cubic pyrochlore phase after thermal treatment at the temperature as low as 450 °C. The aqueous solution–gel method, which Bi, Zn and Nb ions are chelated to form metal complexes, leading to the formation of cubic pyrochlore phase at low firing temperatures. No detectable intermediary phase such as BiNbO₄ or pseudo-orthorhombic pyrochlore is observed in the XRD patterns of ceramics at the sintering temperature range from 850 to 1,000 °C. The dielectric properties study revealed that the ceramics sintered at 900 °C show excellent performance with dielectric constant of 111 and dielectric loss of 2.3871 × 10⁻⁴ under 1 MHz at room temperature.     

Synthesis and microwave dielectric properties of Ca<Subscript>0.6</Subscript>La<Subscript>0.267</Subscript>TiO<Subscript>3</Subscript> nanocrystalline powders by sol–gel method

Ca_0.6La_0.267TiO₃ nanocrystalline powders were successfully synthesized by the sol–gel method using PEG1000 as a dispersant in this study. The sinterability of the powders and the microwave dielectric properties of the ceramics were also investigated. The XRD diffraction result showed that pure Ca_0.6La_0.267TiO₃ powder with orthorhombic perovskite structure could be synthesized at 600 °C for 2 h without any detectable intermediate phase. The average grain size of the as-synthesized powder was as low as 35 nm. Compared with Ca_0.6La_0.267TiO₃ ceramics fabricated by conventional solid-state process, the bulk materials prepared by sintering as-prepared nanopowders performed better in densification and microwave dielectric properties. The ceramics sintered at 1,300 °C exhibited a higher relative density of 98.3% combined with a dielectric constant (ε _r ) of 120.3, a quality factor (Q × f) of 23,550 GHz and a temperature coefficient of resonant frequency (τ _f ) of +220.7 ppm/°C, respectively.     

Dielectric and magnetic properties of multiferroic BiFeO3 ceramics sintered with the powders prepared by hydrothermal method

BiFeO₃ ceramics were sintered in the temperature range of 700–900 °C by using the pure BiFeO₃ powders hydrothermally synthesized at 250 °C. The low reaction temperature and low sintering temperature prevent the element volatilization and phase decomposition. The ceramics sintered at 800 and 850 °C exhibit much dense microstructure with clear grains and grain boundaries. They also show high dielectric constant, dielectric dispersion and low loss tangent. At room temperature, the dielectric behaviors of BiFeO₃ ceramics are mainly attributed to the transition of localized charge carriers and the microstructure of grains and grain boundaries. The temperature dependence of dielectric constant and loss tangent confirms that the localized charge carriers are a main contribution to the dielectric permittivity. Activation energy E_α of relaxation process for the BiFeO₃ ceramic sintered at 850 °C is 0.397 eV. The obtained BiFeO₃ ceramics show magnetic responses, which are relative to the grain size.     

Preparation of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> by polyacrylamide gel processing and its thermoelectric properties

Ca₃Co₄O₉ powder was prepared by a polyacrylamide gel route in this paper. The effect of the processing on microstructure and thermoelectric properties of Ca₃Co₄O₉ ceramics via spark plasma sintering were investigated. Electrical measurement shows that the Seebeck coefficient and conductivity are 170 μV/K and 128 S/cm, respectively, at 700 °C, yielding a power factor value of 3.70 × 10⁻⁴ W m⁻¹ K⁻² at 700 °C, which is larger than that of Ca₃Co₄O₉ ceramics via solid-state reaction processing. The polyacrylamide gel processing is a fast, cheap, reproducible and easily scaled up chemical route to improve the thermoelectric properties of Ca₃Co₄O₉ ceramics by preparing the homogeneous and pure Ca₃Co₄O₉ phase.     

Synthesis of nanoparticles of the giant dielectric material,CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> from a precursor route

A complex oxalate precursor, CaCu₃(TiO)₄(C₂O₄)₈·9H₂O, (CCT-OX), was synthesized and the precipitate that obtained was confirmed to be monophasic by the wet chemical analyses, X-ray diffraction, FTIR absorption and TG/DTA analyses. The thermal decomposition of this oxalate precursor led to the formation of phase-pure calcium copper titanate, CaCu₃Ti₄O₁₂, (CCTO) at ≥680°C. The bright-field TEM micrographs revealed that the size of the as synthesized crystallites to be in the 30–80 nm range. The powders so obtained had excellent sinterability resulting in high density ceramics which exhibited giant dielectric constants upto 40000 (1 kHz) at 25°C, accompanied by low dielectric losses, <0.07.     

Effect of CuO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on low temperature sintered MnZn-ferrite by sol–gel auto-combustion method

A sol–gel auto-combustion method was investigated to incorporate small amounts of additives of Cu and Bi uniformly into soft magnetic MnZn-ferrite nanoparticles, which were prepared by Fe(NO₃)₃·9H₂O, Mn(NO₃)₂ and Zn(NO₃)₂·6H₂O dissolved in water and citric acid. The powder was characterized by the X-ray diffraction analysis and transmission electron microscope method. The effects of nano-particle sized powders in microstructure development and adding CuO–Bi₂O₃ into MnZn-ferrite on phase formation, densification process as well as magnetic properties were studied by scanning electron microscope and vibrating sample magnetometer techniques. The sample without additive can be sintered well at 930 °C, while the samples with a small amount of the additive can be sintered at less than 900 °C. Obviously, the micron-sized powders exhibited high sintering activity. It was also found that CuO–Bi₂O₃ additive promoted the growth of grains and improved magnetic properties. The permeability and the saturation magnetization were improved substantially by adding CuO–Bi₂O₃ into MnZn-ferrite and the sintering temperature was lowered to 875 °C, which may be associated with the redistribution of cations on the tetrahedral (A) sites and octahedral (B) sites within the spinel lattice.     

Phase,crystal struture and sintering behavior of shock-synthesized Pb(Zr0.95Ti0.05)O3 powders

With a cylindrical shock-wave-loading technique, the single perovskite-phase Pb(Zr_0.95Ti_0.05)O₃ powders (PZT 95/5) were synthesized by shock-induced chemical reactions in heterogeneous multi-material powder mixtures of Pb₃O₄, ZrO₂ and TiO₂. The phase and crystal structure of as-synthesized powders were characterized by X-ray diffraction (XRD) and fourier transform infrared (FT-IR) analysis. And the microstructure and electrical properties of PZT 95/5 ceramics prepared with as-synthesized PZT powders at different sintering temperature were analyzed. The results showed that the shock-wave-induced a large quantity of lattice defects and distortion of the crystal structure in the shock-synthesized PZT powders, which could enhance the sintering activity. Thus, the optimal density and electrical properties of PZT ceramics prepared with as-synthesized powders could be obtained at a sintering temperature of 1200–1225 °C for 3 h, significantly lower than the sintering temperature of PZT 95/5 ceramics prepared by conventional solid-state reaction.     

Preparation and characterization of CaCu3Ti4O12 powders by non-hydrolytic sol–gel method

CaCu₃Ti₄O₁₂ (CCTO) powders were prepared via a non-hydrolytic sol–gel (NHSG) method by using acetylacetone as chelating agent and ethylene glycol as solvent. The samples were characterized by TG–DSC, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope. The dielectric properties of ceramics were also measured. The pure perovskite-like CCTO powders were obtained by heat treatment at 800 °C for 2 h. The average particle sizes of CCTO powders calcined at 800 °C were approximately 350–450 nm. The samples sintered at 1,000 °C showed the mean grain size of 2.5–4 μm. Specially, the ceramics exhibited high dielectric constant (1.19 × 10⁵–1.40 × 10⁵) and low dielectric loss (0.051–0.1) in the temperature range of 30–110 °C. Moreover, with the NHSG method the period of synthesis process was greatly shortened.     

Synthesis and characterization of CaTiO3-(Sm,Nd)AlO3 microwave ceramics via sol–gel method

0.65CaTiO₃–0.35Sm_0.9Nd_0.1AlO₃ (CTSA) ceramic nanopowders were synthesized via sol–gel method using the ethylene diamine tetraacetic acid as a chelating agent. Thermal analysis, Fourier transform infrared spectroscopy and X-ray diffraction were used to character the decomposition of precursor and phase transformation process of derived oxide powders. Single phase and well-crystallized 0.65CaTiO₃–0.35Sm_0.9Nd_0.1AlO₃ powders with particle size of 30–40 nm were obtained by calcination at 800 °C. Dense ceramic was successfully obtained from the ultrafine powders sintered at 1,325 °C, almost 100 °C lower than 1,415 °C required for conventional powders. Compared with those prepared by conventional solid-state method, the CTSA ceramics derived from sol to gel process sintered at a lower temperature showed better microwave dielectric properties of ε_r ~ 39, Q × f over 50,000 GHz and small τ_f ~ ?7.1 ppm/K.     

Magnetic properties of doped LaMnO<Subscript>3</Subscript> ceramics obtained by a polymerizable complex method

Substituted lanthanum manganites with the general formula A_1−x B _x MnO₃ (A = La, B = Ca, Sr…) have attracted a lot of attention due to their exceptional electric and magnetic properties. In this work, pure and Ca²⁺, Sr²⁺-doped LaMnO₃ (LMO) with the concentrations of dopants 30% Ca²⁺ (LCMO), 30% Sr²⁺ (LSMO) and 15% Ca²⁺ + 15% Sr²⁺ (LCSMO) (in mol. %) were synthesized by polymerizable complex method. Bulk samples were prepared by sintering at 1300 °C for 4 h in oxygen atmosphere. It was found that sintering in oxygen atmosphere enables preparation of single phase ceramics with rhombohedral crystal structure. Chemically prepared fine, submicronic precursor powders provided uniform microstructure and grain size distribution in final ceramics. As a result, pure and doped LMO ceramics with excellent microstructural and magnetic properties were obtained. Depending on the composition, magnetic measurements showed high saturation magnetizations (up to 93 emu/g), with values of the Curie temperature in the range 180–390 K and magnetoresistance up to 67%.     

Ceramic and Transport Characteristics of Electrolytes Based on Mg-Doped LaYO<Subscript>3</Subscript>

Effect of magnesium on the sinterability, phase composition, microstructure, and transport properties of proton-conducting materials of composition LaY_1–xMg_xO_3–δ (х = 0, 0.05, 0.1) was studied. Ceramic samples were obtained by using the citrate-nitrate synthesis method at various sintering temperatures (1250–1400°C). It was shown that, for the samples with x = 0.05 and 0.1, the relative density was no less than 95% at a sintering temperature of 1350°C, whereas undoped lanthanum nitrate has this density at 1450°C. An X-ray diffraction analysis and scanning electron microscopy demonstrated that introduction of a small amount of magnesium (x = 0.05) is sufficient for forming the single-phase and high-dense ceramics. Electrical conductivity data show that the LaY_0.95Mg_0.05O_3–δ sample has high overall and ionic conductivities.     

Influence of barium source on the characteristics of sol-precipitated BaTiO<Subscript>3</Subscript> powders and related ceramics

In order to obtain pure and fine BaTiO₃ powders with controlled morphology, sol-precipitation methods involving the use of titanium iso-propoxide and of two different barium sources, i.e. barium nitrate and barium acetate, were proposed in this work. The thermal behaviour of the synthesized gels and the X-ray diffraction data obtained for the oxide powders pointed out that, by using Ba(NO₃)₂ as barium source, the decomposition process was completed at lower temperature (750°C) and was accompanied by a more pronounced tendency to obtain a single phase BaTiO₃ composition, by comparison with the synthesis where barium acetate was used as raw material (1100°C). Scanning electron microscopy investigations emphasized the effect of the nature of barium source and synthesis conditions on the morphology of the oxide powders, as well as on the microstructure of the related ceramics.     

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.     

Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> powders by the complex polymerization method: synthesis,characterization and morphology

Lanthanum-modified bismuth titanate (Bi_3.25La_0.75Ti₃O₁₂, BLTO) powders were prepared by the complex polymerization method. The structure and morphology of BLTO powders were investigated by X-ray diffraction and scanning electron microscopy. The complexation of citric acid with the metallic cations was detected by Fourier transformed infrared (FT-IR). The thermal analyses of obtained gels were investigated by differential thermal gravimetric (DTG). The pure and normally stoichiometric phase of BLTO powders could be obtained at relatively low temperature of 550–700 °C even if the bismuth content is not excess in the starting precursors, while the secondary phase could be detected at lower and higher calcination temperatures. The shape of the BLTO grains is similarly to platelet in Bi-layer structure and stoichiometry BLTO was detected by the analysis of energy dispersive spectrometry.     

Microstructure and electrical properties of lead zirconate titanate thin films deposited by sol-gel method on La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrate

(La_0.7Sr_0.3)MnO₃ thin films were deposited on SiO₂/Si substrates by a metal-organic decomposition (MOD) method, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were grown on (La_0.7Sr_0.3)MnO₃-coated SiO₂/Si substrates by a sol-gel method. The effects of annealing temperature on the crystalline phases, microstructures and electrical properties of the PZT films were investigated. X-ray diffraction analysis results indicated that the PZT films with a perovskite single phase could be obtained by annealing at 650°C. The dielectric constant and the remnant polarization of the PZT films increased with increasing annealing temperature. The remnant polarization and the coercive field of the films annealed at 650°C were 18.3 μC/cm² and 35.5 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.81, respectively.     

An aqueous solution-gel method for low temperature synthesis of nanocrystalline NaNbO<Subscript>3</Subscript> and their ceramics

Nano-sized NaNbO₃ powder has been successfully prepared by aqueous solution-gel method. The phase evolution of NaNbO₃ powder is investigated by TG/DSC, X-rays spectra, FT-IR, and Raman spectra. The results show that the pure NaNbO₃ phase has been obtained at about 375 °C, which is lowered by about 100 °C comparing to others’ work. In TEM studied, it shows the average particle size of ~ 70 nm for the powders heat-treated at 750 °C for 4 h. The powders heat-treated below 650 °C for 4 h shows a Pmnm symmetry, then change from O₃ orthorhombic to O₁ orthorhombic with the heat-treatment temperature above 650 °C.     

BaBi2Nb2O9 powder and their ceramics prepared by aqueous solution–gel method

BaBi₂Nb₂O₉ powders and their ceramics were prepared by aqueous solution?Cgel method. The phase evolution and microstructure of samples including powders and ceramics were determined by X-rays, SEM. An homogenous BaBi₂Nb₂O₉ powder was observed after thermal treatment at the temperature as low as 400?°C. The texture phenomena has been observed in the ceramics during the process of sintering, the size and area of oriented grains increased with increase the sintering temperature, and the grain growth occurs in preferential direction which is parallel to the plane of the ceramic plate. The density of this ceramics has been determined, the study revealed that the density increases with sintering temperature and reached a maximum at 1,000?°C and then decreases gradually. The characteristic diffuse phase transition of the BaBi₂Nb₂O₉ ceramics was observed at about 200?°C.     

Microstructure and dielectric properties of Nd doped CaCu3Ti4O12 synthesized by sol–gel method

Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ (x = 0, 0.1, 0.2 and 0.3) powders and ceramics were prepared by sol–gel method. Effect of Nd on microstructure and dielectric properties were investigated. XRD patterns suggest that pure perovskite-like CCTO phase were obtained after calcining at 800 °C for 2 h. SEM pictures reveal that particle size monotonously decreases from 250 to 120 nm with increase of Nd concentration. The lattice parameters show an increasing trend with the enhancing amount of Nd³⁺ substitution. The average grain size of CCTO ceramics decrease from 2.0 to 0.8 μm with increase in Nd doping, which indicates that high concentration of Nd inhibits grain growth of CaCu₃Ti₄O₁₂. Both of the dielectric constant and dielectric loss decrease with increase in Nd concentrations. Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ ceramics with x = 0.3 shows the lowest dielectric constant of 1.12 × 10⁴ as well as the lowest dielectric loss value of 0.12 at 20 °C(10 kHz).     

Effects of molecular weight,heating rate,synthetic temperature and sintering duration on electrochemical properties of a LiFePO<Subscript>4</Subscript>/C cathode material pyrolyzed from lithium polyacrylate

A LiFePO₄/C composite was obtained by a polymer pyrolysis reduction method, using lithium polyacrylate (LiPAA) as carbon source and fractional lithium source, and FePO₄·2H₂O as iron and phosphorus source. The structure of the LiFePO₄/C composites was investigated by X-ray diffraction (XRD). The micromorphology of the precursors and LiFePO₄/C powders was observed using scanning electron microscopy (SEM). Laser particle analyzer and BET were also used to characterize the materials. It was found that the micromorphology, particle size distribution and specific surface area of LiFePO₄/C composites were greatly influenced by the molecular weight of LiPAA. The electrochemical properties of the LiFePO₄/C composites were evaluated by cyclic voltammograms (CVs), electrochemical impedance spectra (EIS) and constant current charge/discharge cycling tests. The results showed that the molecular weight of LiPAA, heating rate, synthetic temperature and sintering duration directly affected the electrochemical properties of LiFePO₄/C composites. The sample with the optimized electrochemical properties were obtained in the following conditions, i.e., LiPAA with the molecular weight of 20,000, heating rate of 10 °C min⁻¹, synthetic temperature of 700 °C and sintering duration of 15 h.