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.     

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.     

Effect of the Different Sr Dopant Contents on NiO Ceramic

Sr - doped NiO ceramic was studied. The effect of composition variation of Ni_(1-x)Sr_xO where x = 0, 0.01, 0.02, 0.03, 0.05 and 0.10 mole % was prepared by using solid state method. The calcination temperature used at 950 °C for 4 hours and the sintering temperature used at 1200 °C for 3 hours. The results depict the microstructures increase in grains size (0.43 - 3.30 μm) by increase of Sr dopant contents. The density and porosity testing support the result of microstructures analysis. The larger grains size led to increase in density and lower in porosity. The dielectric properties is observed in a wide frequency range of (1 - 1 000 MHz). The increase of dielectric constant is associated with the decrease of dielectric loss. The optimum composition was obtained for the x = 0.03 mole % sample with highest dielectric constant (3.24 x 10³) and lowest dielectric loss (1.42) at 1 MHz.     

Characterization of poly(vinyl chloride) powder produced by emulsion polymerization

The effect of emulsion process formulation ingredients on the morphology, structure, and properties of polyvinyl chloride (PVC) powder has been considered in this study. PVC powder was extracted with ethanol and films were obtained by solvent casting from tetrahydrofurane. Characterization of powders, films, and ethanol extract was performed through FTIR spectroscopy, DSC, AFM, SEM, EDX analysis, methylene blue, and nitrogen adsorption. PVC powder was composed of spheres of a large particle size range from 10 nm to 20 μm as shown by SEM. The specific surface area of the PVC powder was determined as 16 and 12 m² g⁻¹ from methylene blue adsorption at 25 °C and from N₂ adsorption at −196 °C, respectively. AFM indicated the surface roughness of the films obtained by pressing the particles was 25.9 nm. Density of PVC powder was determined by helium pycnometry as 1.39 g cm⁻³. FTIR spectroscopy indicated that it contained carbonyl and carboxylate groups belonging to additives such as surface active agents, plasticizers, and antioxidants used in production of PVC. These additives were 1.6% in mass of PVC as determined by ethanol extraction. EDX analysis showed PVC particles surfaces were coated with carbon-rich materials. The coatings had plasticizer effect since, glass transition temperature was lower than 25 °C for PVC powder and it was 80 °C for ethanol extracted powders as found by using differential scanning calorimetry. These additives from polymerization process made PVC powder more thermally stable as understood from Metrom PVC thermomat tests as well.     

Effect of curing on the broadband dielectric spectroscopy of powder coating

The effect of curing process of thermosetting powder coating consists of carboxylated polyester resin cured with triglycidyl isocyanurate has been investigated using broadband dielectric relaxation spectroscopy over a wide range of frequency (10⁻¹-10⁶ Hz) and temperature (70-105 °C) for different constant curing times. The molecular dynamics of the glass relaxation process (α-process) was investigated as a function of curing time, frequency, and temperature. It has been found that, only one common α-relaxation process has been observed for all measured samples of different degree of curing stages, its dynamics and broadness were found to be curing time dependent. In addition, the curing time dependence of the dielectric relaxation strength, Δε, has also been examined for the α and β-relaxation processes. The Δε for the two relaxation processes decreased strongly at the beginning of curing process and then became almost constant at longer curing times. This finding implied that the numbers of reoriented dipoles decrease with curing time as a result of the formation of three-dimensional polymer network. Furthermore, the dislocation energy, ε_s, calculated from the Meander model was found to be increased with increasing the curing time, i.e. the formation of a three-dimensional polymer network produces many structural defects or dislocation points. In addition, the activation energy of the curing process was calculated from the analysis of the calorimetric exothermic peaks of the curing process at different heating rates.     

Giant dielectric constant response of the composites in ternary system CuO-TiO2-CaO

The subsolidus phase relations of the ternary system CuO-TiO₂-CaO sintered at 950 °C in air have been determined by powder X-ray diffraction method. Only one ternary compound CaCu₃Ti₄O₁₂ was found in this system. From room-temperature dielectric property mapping at 10 kHz, a giant dielectric constant (ε_r>10⁴) was observed for most of the ceramic composites in the CuO-rich region and in the region along the CaO-CuO binary line. The composites in the CaCu₃Ti₄O₁₂-rich region were found to give a comparable giant dielectric constant when sintered at 1050 °C. The particular microstructure of larger grains with predominant phase surrounded by smaller grains with the secondary phases was found in such composites with a high dielectric constant. The relations between structures and dielectric properties were investigated. An internal barrier layer capacitance effect is the most probable mechanism to explain this particular dielectric behavior.     

Dielectric spectroscopy of nanocomposites based on iPP and aPS treated in the water solutions of alkali metal salts

In this paper, a new simple and environmentally friendly treatment technique for obtaining polymer nanocomposites with appropriate dielectric properties has been presented. Sheets of isotactic polypropylene and atactic polystyrene were immersed in 3 saturated water solutions of alkali metal salts (LiCl, NaCl, and KCl) at 2 fixed temperatures (23°C and 90°C), and 3 DC electrical potentials (+4 kV, −4 kV, and ground potential) were applied. A quantification of alkali metals in the polymer sheets was conducted by inductively coupled plasma optic emission spectrometry. The obtained concentration values were from 7.38·10⁻⁹ mol/cm³ to 1.25·10⁻⁷ mol/cm³. The qualitative analysis of potassium distribution in the polymer matrix was conducted by time‐of‐flight secondary ion mass spectrometry cross‐sectional record. The relative dielectric constant (ε′) of samples was investigated in the frequency range from 20 Hz to 9 MHz at the constant temperature of 22°C. Stable values of ε′ in fully measured frequency range were observed for both pure and treated samples. Next, the results of the dielectric spectroscopy measurements were compared and established the kind of treatment that provided the highest value of ε′. The relationship between the concentrations of alkali metals and the values of relative dielectric constant was determined for the samples obtained by a treatment at 90°C and +4 kV.     

Novel conducting poly(3,4-ethylenedioxythiophene) – Graphene nanocomposites with gigantic dielectric properties and narrow optical energy band gap

Novel nanocomposites, consisting of conducting poly(3,4-ethylenedioxythiophene) [PEDOT] and graphene nanoplatelets [GNPs], were successfully synthesized by in-situ chemical-oxidative polymerization of 3,4-ethylenedioxythiophene [EDOT] using ammonium peroxydisulfate as an oxidizing agent. The formation of PEDOT and its incorporation onto the surface of GNPs were confirmed by scanning electron microscopy, Fourier-transform infrared-spectroscopy, and X-ray diffraction. The optical energy band gap, E_g^opt, was determined by UV–Vis spectroscopy. Dielectric constant and loss as well as AC electrical conductivity, σ_AC, were determined in the frequency range from 10 Hz to 8 MHz. The PEDOT-GNP nanocomposites were found to have extremely large dielectric constant, ε′, significantly high σ_AC, and narrow E_g^opt values. In particular, PEDOT-GNP nanocomposite with 10 wt% GNP has a gigantic dielectric constant of the order of 9 × 10⁵ at 1 kHz and a narrow optical energy band gap of 1.26 eV. The ε′ values (10⁸ to 10⁵ in the frequency range from 10 Hz to 5 MHz) of PEDOT-10 wt% GNP are the highest among those reported in the literature for carbon based polymer nanocomposites. The massive quantity of micro-capacitors formed in the nanocomposites, prior to the creation of conductive networks, leads to the gigantic dielectric properties. The ε′ and σ_AC values of PEDOT-10 wt% GNP nanocomposite were about 90 and 400 times larger than those of pure PEDOT. Our method should be particularly promising in the development of new materials for high energy storage applications.     

Impedance spectroscopy of V2O5–Bi2O3–BaTiO3 glass–ceramics

The glasses within composition as: (80 − x)V₂O₅/20Bi₂O₃/xBaTiO₃ with x = 2.5, 5, 7.5 and 10 mol% have been prepared. The glass transition (T_g) increases with increasing BaTiO₃ content. Synthesized glasses ceramic containing BaTi₄O₉, Ba₃TiV₄O₁₅ nanoparticles of the order of 25–35 nm and 30–46 nm, respectively were estimated using XRD. The dielectric properties over wide ranges of frequencies and temperatures were investigated as a function of BaTiO₃ content by impedance spectroscopy measurements. The hopping frequency, ω_h, dielectric constant, ε′, activation energies for the DC conduction, E_σ, the relaxation process, E_c, and stretched exponential parameter β of the glasses samples have been estimated. The, ω_h, β, decrease from 51.63 to 0.31 × 10⁶ (s⁻¹), 0.84 to 0.79 with increasing BaTiO₃ respectively. Otherwise, the E_σ, increase from 0.279 to 0.306 eV with increasing BaTiO₃. The value of dielectric constant equal 9.5·10³ for the 2.5BaTiO₃/77.5V₂O₅/20Bi₂O₃ glasses-ceramic at 330 K for 1 KHz which is ten times larger than that of same glasses composition. Finally the relaxation properties of the investigated glasses are presented in the electric modulus formalism, where the relaxation time and the respective activation energy were determined.     

Study of the formation of the apatite-type phases La9.33+x(SiO4)6O2+3x/2 synthesized from a lanthanum oxycarbonate La2O2CO3

Lanthanum silicated apatites with nominal composition La_9.33+x(SiO₄)₆O_2+3x/2 (−0.2 < x < 0.27) have been successfully synthesized by solid state reaction using a new reagent La₂O₂CO₃ and amorphous SiO₂ precursors. The formation mechanism of La₂O₂CO₃ reagent, which cannot be purchased, has been followed by in-situ temperature depend XRD of La₂O₃ under CO₂ atmosphere. The stability of this reagent during the synthesis step allowed to limit the formation of secondary phase La₂Si₂O₇ and made the weighting of the reagent easier. High purity powders could be synthesized at the temperature of 1400 °C. Dense pellets (more than 98.5%) were obtained by isostatic pressing of powders calcined at 1200 °C and then sintered at 1550 °C. Traces of La₂SiO₅ secondary phase present in synthesized powder disappeared after densification and pure oxyapatite materials were obtained for all the compositions. Electrical measurements confirmed that conductivity behaviors of the sintered pellets were dependent to the oxygen over-stoichiometry. Indeed, a relatively high conductivity of 1 × 10⁻² S cm⁻¹ was exhibited at 800 °C for the nominal composition La_9.60(SiO₄)₆O_2.405 with low activation energy around 0.79 eV. The ionic conductivity properties were comparable with that of the earlier obtained materials.     

Effect of phase purity on dielectric properties of CaCu3+xTi4O12 ceramics

Different amounts of CuO are used to synthesize CaCu_3+xTi₄O₁₂ (CC_xTO, −1 ≤ x ≤ 1) powders in this work. In order to investigate the effects of Cu constituent on the componential, morphological, and dielectric properties, 975 °C is selected as the sintering temperature to prepare the ceramic pellets with different x values from −0.2 to 0.2. They basically keep the same component and morphology despite the different Cu constituents in the ceramics. Cu component has complex effects on their dielectric properties, whose changes are not linear with the Cu increase. However, the CC_0.2TO ceramic sample has the most frequency-independent dielectric constant and the lowest dielectric loss.     

Determination of Active Metal in Ultradispersed Iron Powders and TG Study of Their Oxidation

Two oxidation stages of electrolytic ultradispersed iron powder at the temperature range of 90–450°C have been stated. The contribution of increasing mass and evolving heat at the first oxidation stage due to changing Fe⁰ into Fe₂O₃ in the total oxidation effect is predominant. The thermal method of active metal determination in electrolytic iron powders has been developed. The coarse-grained reduced iron powder was not oxidized completely just to 900°C because of local sintering of big iron particles as a result of evolving heat at oxidation of high-dispersed iron particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dielectric spectroscopy of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) films

In this paper, we report a systematic study of the dielectric relaxation spectroscopy of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) polyester which has potential applications as a “green” dielectric material in electronic devices. The dielectric spectra was measured over a wide frequency range (10⁰ ～ 10⁷ Hz) from ?100 to 60 °C. A glass and a sub-glass transition relaxations were observed in the dielectric spectra of PHBHHx. In addition, a nearly constant loss behavior was found by analyzing the dielectric and conductivity spectra.     

A study of scandia and rhenium doped tungsten matrix dispenser cathode

Scandia and rhenium doped tungsten powders were prepared by solid–liquid doping combined with two-step reduction method. The experimental results show that scandia was distributed evenly on the surface of tungsten particles. The addition of scandia and rhenium could decrease the particle size of doped tungsten, for example, the tungsten powders doped with Sc₂O₃ and Re had the average size of about 50 nm in diameter. By using this kind of powder, scandia and rhenium doped tungsten matrix with the sub-micrometer sized tungsten grains was obtained. This kind of matrix exhibited good anti-bombardment insensitivity at high temperature. The emission property result showed that high space charge limited current densities of more than 60 A/cm² at 900 °C could be obtained for this cathode. A Ba–Sc–O multilayer about 100 nm in thickness formed at the surface of cathode after activation led to the high emission property.     

Dielectric behavior and impedance analysis of lead-free CuO doped (Na0.50K0.50)0.95(Li0.05Sb0.05Nb0.95)O3 ceramics

Pure (Na_0.50K_0.50)_0.95(Li_0.05Sb_0.05Nb_0.95)O₃ (NKNLS) and CuO doped NKNLS perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. x wt% of CuO (x = 0.2–0.8 wt%) was added in the NKNLS ceramics. X-ray diffraction patterns indicate that single phase was formed for pure NKNLS while a small amount of second phase (K₆Li₄Nb₁₀O₃₀ ∼ 3%) was present in Cu²⁺ doped NKNLS ceramics. Dielectric anomalies around the temperatures of 120 °C and 350 °C have been identified as the ferroelectric–paraelectric transition (orthorhombic to tetragonal and tetragonal to cubic) temperatures for pure NKNLS compound. The electrical behavior of the ceramics was studied by impedance study in the high temperature range. Impedance analysis has shown the grain and grain boundary contribution using an equivalent circuit model. The impedance response in pure and Cu²⁺ doped NKNLS ceramics could be resolved into two contributions, associated with the bulk (∼grains) and the grain boundaries. From the conductivity studies, it is found that activation energies are strongly frequency dependent. The activation energy obtained from dielectric relaxation data may be attributed to oxygen ion vacancies.     

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.     

Complex dielectric constant and relaxation parameters of aqueous solutions of barium nitrate

Microwave dielectric properties of aqueous solutions of barium nitrate are studied as a function of concentration at frequencies from 3.4 to 23.5 GHz and temperatures from 283 to 313 K. The following dielectric parameters of the solutions are determined: static dielectric constant ε_s, dielectric relaxation time τ, and enthalpy of activation of dielectric relaxation ΔH _ε ⁺⁺ . In transfer from water to the solutions, the static dielectric constant decreases for all test solutions. Decreases in τ and ΔH _ε ⁺⁺ are induced by the increasing mobility of water molecules in ion hydration shells. The ionic effect disappears as temperature increases.     

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 spectroscopic analysis of polyvinyl chloride nanocomposites loaded with Fe2O3 nanocrystals

Iron oxide (α‐Fe₂O₃) nanocrystals powder was successfully synthesized via the sol‐gel method. The microstructural examination of the synthesized nanocrystals confirmed the formation of α‐Fe₂O3 (hematite) structure using X‐ray diffraction and Fourier transform infrared. The synthesized nano‐hematite powder with different weight percentage up to 5 wt% was introduced to polyvinyl chloride (PVC) to fabricate PVC/Fe₂O₃ nanocomposites using the solution‐cast technique. The dielectric spectroscopic analysis for the investigated samples has been studied at room temperature and at different temperatures up to 120°C. The real part of the permittivity (ε^′) exhibited a significant dependence on filler concentrations throughout whole temperature range. However, the dependency of both of the loss tangent (tanδ ) and AC conductivity (σ_ac) on filler concentrations is more pronounced at temperatures higher than room temperature. The obtained values of tan δ for the investigated nancomposites referred to the α‐relaxation around 70°C, which is close to glass transition temperature of the investigated PVC. The dependency of the dielectric strength on Fe₂O₃ nanofiller concentration was observed with enhancement in the dielectric strength reach to 20.5% for PVC/0.7 wt% Fe₂O₃ nanocomposite higher than the recorded value for the pristine PVC.