Magnetic properties and thermal behavior of mullite–iron nanocomposite powders

Mullite based iron magnetic nanocomposite powders were synthesized by reduction of sol–gel prepared mullite–iron oxide solid solution in hydrogen flow. Structural characterization studied by TEM revealed that two types of α-iron nanoparticles existed in mullite matrix. The α-iron nanoparticles with the size around hundreds of nanometers appeared as inter-type grains, while those around 10 nm were embedded in the grains of mullite. The magnetic properties of nanocomposites suggest that the intergranular and intragranular α-iron nanoparticles had the ferromagnetic and superparamagnetic behavior at room temperature, respectively. The oxidation behavior of nanocomposite powders showed that there existed two different oxidation stages of α-Fe nanoparticles.     

Study on the preparation of battery grade cobalt carbonate from PTA oxidation residue

ABSTRACT

The oxidation residue coming from the process of production of PTA is an important secondary resources. PTA residue was used as raw material, and the battery grade cobalt carbonate was made after removing manganese. The optimum conditions on the precipitating cobalt by using sodium sulfide and the removing manganese by oxidation precipitation were investigated. The results demonstrate that the maximum sulfide precipitation rate of cobalt is 99.9%, when the amount of sodium sulfide is 1.8 times of the theoretical chemical reaction, pH 3, temperature 20°C and reaction time 1 h. When the reaction time is 1 h, the amount of sodium persulfate 4 times of the theoretical amount and pH 3, the oxidation precipitation rate of manganese can reach 99%. After the processes of sulfide precipitation of cobalt and oxidation precipitation of manganese, the battery grade cobalt carbonate was prepared. The purity of the battery grade cobalt carbonate is greater than 99.9%.     

Microstructure of cobalt oxide doped sintered ceria solid solutions

The sintering of ceria solid solutions, such as Ce_0.9Gd_0.1O_1.95 (CGO10), is strongly promoted by the addition of 1 cat% of cobalt oxide, lowering the maximum sintering temperature by 200^∘C and triplicating the maximum densification rate. This change in sintering behavior results from cobalt ion segregated at the grain boundaries. An average cobalt ion boundary coverage is at maximum 3.0 ± 1.9 at/nm² and is shown to depend on the cooling rate. Coverage by segregated gadolinium is also found and amounts to 13.2 ± 11.4 at/nm² for a slowly cooled sample. From cobalt excess measured at the boundary, an estimated concentration of only 0.06 cat% of cobalt oxide is necessary to promote the sintering effect. The remaining amount of cobalt oxide is found in triple points and as particles in clusters. It is expected that the amount of cobalt oxide necessary for fast densification can be reduced with a doping process that distributes the additives more homogeneously.     

Improved energy density and dielectric properties of P(VDF-HFP) composites with TiO<Subscript>2</Subscript> nanowire clusters

Dielectric composites are of great demand in the micro-electronics industry. To enhance the energy storage density of the composites, TiO₂ nanowire clusters was synthesized by a hydrothermal method and incorporated into the P(VDF-HFP) polymer matrix in this work. The microstructure, dielectric properties of the prepared film were discussed and the effects of TiO₂ loading on the energy density were investigated. The results shows that the TiO₂ clusters were tightly blended to the P(VDF-HFP) matrix owing to the dopamine-modified interface. The dielectric constant increased with the loading of TiO₂, the maximum dielectric constant reached 12.04 with 7.5 vol% TiO₂ loading at 1 kHz, as compared to 5.01 for the neat P(VDF-HFP). The enhanced dielectric constant was attributed to the interface polarization originated from the large interface area between the TiO₂ nanowire and polymer matrix. The discharged energy density of the composite significantly increased to 1.35 J/cm³ with 7.5 vol% TiO₂ nanowire clusters, which was two times higher than that of the neat P(VDF-HFP) at the same condition. The findings of this work can shed a light on improving the energy density of energy storage device via morphology modification.     

Effects of cobalt addition on structural,thermal and electrical properties of praseodymium-yttrium co-doped barium cerates

Effects of cobalt addition on structural, thermal and electrical properties of praseodymium-yttrium co-doped barium cerates have been investigated. Relative densities >98 % have been achieved after sintering at 1400 °C or 1500 °C for only 1 h. All studied compounds are stable in ambient air up to the measured 900 °C and, in reducing atmosphere (both wet and dry 5 % H₂-Ar) up to the measured 800 °C. The Co-free sample (BaCe_0.7Y_0.2Pr_0.1O_3-δ) exhibits the highest conductivity of 1.21?×?10^?2 S cm^?1 at 700 °C in air while the corresponding cobalt containing sample (BaCe_0.7Y_0.175Pr_0.1Co_0.025O_3?δ) has a conductivity of 9.85?×?10^?3 S cm^?1 at 700 °C in air. Cobalt addition allows the ability to retain much larger amounts of water to be retained as suggested by the higher conductivities obtained in wet hydrogen compared to the values in dry reducing atmosphere. This latter phenomenon is of special interest as it suggests the possibility of higher ionic conductivities in water-containing atmosphere and would benefit to intermediate- and high-temperature solid oxide fuel cells and/or electrolysers. The thermal expansion coefficients for the Co-free and Co-containing samples were around 12.0?×?10^?6 K^?1 between 25 and 1000 °C.     

Structure dependence of the ferroelectric properties of Bi3.25Ln0.75Ti3O12 (Ln=La, Nd, Sm, Dy) ceramics

We have fabricated rare-earth ion substituted bismuth titanate (BIT) ceramics, Bi_3.25Ln_0.75Ti₃O₁₂ (BLnT; Ln=La, Nd, Sm, Dy), using the conventional solid-state reaction method and have investigated the changes in the structural distortion and electrical properties, which resulted from the substitution of the rare-earth ions in BIT ceramics. As the ionic radius of the rare-earth ion substituted into the BIT decreased, the structural distortion and decreases in the unit cell volume became more pronounced as well as the Curie temperature increased monotonically from 354 °C (BLaT) to 480 °C (BDyT). BNdT ceramics had relatively high remanent polarization value (12.5 μC/cm²) at an applied electric field of 130 kV/cm. The extent of the structural distortion influenced the dielectric and ferroelectric properties of the BLnT ceramics.     

Structural, dielectric and electrical studies of MgAl2−2xY2xO4 (x = 0.00–0.05) cubic spinel nano aluminate

Investigations were carried out on a series of MgAl_2-2xY_2xO₄ (x?=?0.00–0.05) nanoparticles prepared in steps of 0.01 by chemical co-precipitation method to study the effect of yttrium substitution at aluminum site on the structural, dielectirc and electrical properties. The single phase cubic spinel structure of all the samples was confirmed by X-ray diffraction (XRD). The Fourier transform infrared spectroscopy (FTIR) study shows two strong absorption bands in the frequency range 400–800 cm^?1, on the tetrahedral and octahedral sites respectively. Elemental analysis by Energy dispersive X-ray fluorescence (EDXRF) shows that samples are stoichiometric. The scanning electron microscopy (SEM) study reveals surface morphology of nanoparticles. Transmission electron microscopy (TEM) study shows the individual nanoparticles size and validates the nanocrystalline nature of the samples. The variation of dielectric permittivity at room temperature as a function of frequency (1 KHz to 1 MHz) suggests the dielectric dispersion due to Maxwell-Wagner Interfacial Polarization. AC conductivity study reveals that the conduction is due to small polaron hopping. The electrical modulus analysis shows that nanocrystalline MgAl_2?2xY_2xO₄ system exhibits non Debye type relaxation. The dc resistivity was found to increase with increase in yttrium content.     

High dielectric permittivity of SrBi2Nb2O9(SBN) added Bi2O3 and La2O3

In this paper, the structural and dielectric properties of SrBi₂Nb₂O₉ (SBN) as a function of Bi₂O₃ or La₂O₃ addition level in the radio (RF) and microwave frequencies were investigated. The SBN, were prepared by using a new procedure in the solid-state reaction method with the addition of 3; 5; 10 and 15 wt.% of Bi₂O₃ or La₂O_3. A single orthorhombic phase was formed after calcination at 900 °C for 2 h. The analysis by x-ray diffraction (XRD) using the Rietveld refinement confirmed the formation of single-phase compound with a crystal structure (a?=?5.5129 Å, b?=?5.5183 Å and c?=?25.0819 Å; α?=?β?=?γ?=?90°). Scanning Electron Microscope (SEM) micrograph of the material shows globular morphologies (nearly spherical) of grains throughout the surface of the samples. The Curie temperature found for the undoped sample was about 400 °C, with additions of Bi³⁺, the temperature decreases and with additions of La³⁺ the Curie temperature increased significantly above 450 °C. In the measurements of the dielectric properties of SBN at room temperature, one observe that at 10 MHz the highest values of permittivity was observed for SBN5LaP (5%La₂O₃) with values of 116,71 and the lower loss (0.0057) was obtained for SBN15LaP (15%La₂O₃). In the microwave frequency region, Bi₂O₃ added samples have shown higher dielectric permittivity than La₂O₃ added samples, we highlight the SBN15BiG (15 % Bi₂O₃) with the highest dielectric permittivity of 70.32 (3.4 GHz). The dielectric permittivity values are in the range of 28–71 and dielectric losses are of the order of 10^?2. The samples were investigated for possible applications in RF and microwave components.     

Magnetic properties of ZnO-doped cobalt ferrite

The cobalt ferrites with chemical composition Co_1+x Zn _x Fe_2?2x O₄ (x?=?0.0, 0.1, 0.2, 0.4) were obtained with conventional solid reaction. The ZnO-doped samples have lower lattice constant than CoFe₂O₄ by adjusting Co ions to the octahedral sites. The results show that doping ZnO could extremely improve the magnetic properties. In comparison with pure CoFe₂O₄, the little ZnO-doped sample has higher permeability and much lower coercivity at the condition of a little decrease of magnetization saturation. Sample with x?=?0.1 shows evident magnetostrictive effect at the magnetic field of 30–60 mT while pure cobalt ferrite sample does not, though the saturation magnetostriction decreases. These indicate that ZnO-doping improves the magnetostrictive sensitivity of the cobalt ferrites and have potential applications in magnetoelectric devices and magnetic detector.     

One-pot synthesis of mixed-valence MoO x on carbon nanotube as an anode material for lithium ion batteries

A mixed-valence MoO _x /carbon nanotube nanocomposite was synthesized using a one-pot microwave-assisted hydrothermal reaction in which 5 nm MoO _x nanoparticles were coated on the surfaces of carbon nanotube. The MoO _x nanoparticles in the nanocomposite had mixed Mo⁴⁺ and Mo⁶⁺ valence states. Thus, the nanocomposite showed a discharge behavior corresponding to both MoO₂ and MoO₃. The nanocomposite had a reversible discharge capacity of 900 mAh g^?1 at a current density of 90 mA g^?1, and could deliver discharge capacities of 770, 700, and 570 mAh g^?1 at current densities of 450, 900, and 1800 mA g^?1, respectively.     

Self-assembly and hydrothermal technique syntheized Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-RGO nanocomposite: The enhancement effect of electrochemical simultaneous detection of honokiol and magnolol

The nanocomposite of Fe₂O₃-reduced graphene oxide (Fe₂O₃-RGO) was synthesized by a hydrothermal reduction using self-assembly of Fe(OH)₃ colloidal suspension and graphene oxide (GO) as precursors at 180°C. The resulting composites were characterized using XRD, SEM, FTIR, and TGA, and then were used to modify the glassy carbon electrode (GCE). After optimizing the parameters, the electrochemical behavior of honokiol and magnolol on different types of electrode was compared, which indicated that the Fe₂O₃-RGO composite-modified GCE enhanced electrochemical catalysis effect on the simultaneous determination of honokiol and magnolol. In pH 6.4 PBS solution, two well-shaped oxidation peaks at 0.51 and 0.64 V were observed at the Fe₂O₃-RGO composite-modified GCE and two well-shaped oxidation peaks were separated absolutely, which eliminated the disturbance between them. A sensitive and simple electrochemical method was proposed for the simultaneous determination of honokiol and magnolol. As to honokiol, the calibration curve is from 1.5 × 10^?8 ~ 3.3 × 10^?5 M, and the detection limit is 9.64 × 10^?9 M. For magnolol, the linear range is from 7.5 × 10^?8 ~ 2.6 × 10^?5 M, and the detection limit is 1.05 × 10^?8 M.     

Sintering and dielectric properties of (Ta2O5)1−x (TiO2) x polycrystalline ceramics

(Ta₂O₅)_1?x (TiO₂) _x system ceramics has been studied intensively as a promising dielectric material for next generation of high density dynamic random access memories instead of SiO₂ and Si₃N₄. It is found that the dielectric permittivity of (Ta₂O₅)_1?x (TiO₂) _x ceramics was dependent of fabrication process. But in the previous work, their calcining and sintering time were too long, generally for 24 h or even more. A relatively quick sintering process was provided which calcining and sintering time can be decreased to 12 h at 1200°C and 1 h at 1550°C, respectively. This kind of sintering process can save a lot of energy and time that is in favor of the industrial production. Under this sintering process, the composition dependent dielectric properties of (Ta₂O₅)_1?x (TiO₂) _x ceramics have been studied in a wide range of composition (0.01?≤?x?≤?0.20), and the dielectric constants of most compositions can be drastically enhanced. The maximum dielectric value can reach 216 at composition x?=?0.04. In the meantime, the mechanism of improvement of ceramic dielectric constants sintered at 1550°C was also discussed.     

Dielectric characteristics investigation of (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 ferroelectric thin films

By the radio frequency (RF) magnetron sputtering methods, (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ (BSTZ) ferroelectric thin films were deposited on the Pt/Ti/SiO₂/Si(100) substrates. The crystal structural and microstructure of these thin films were analyzed by means of the XRD, SEM, and AFM. Moreover, the dielectric characteristics were also investigated by the C-V and J-E analyses. The optimal deposition parameters for these BSTZ thin films were: RF power is 160 W, oxygen concentration is 25%, substrate temperature is 580°C, and chamber pressure is 0.075 mPa. Under these optimal deposition conditions, the (111) and (110) oriented polycrystalline of the BSTZ thin films grow easily. And under a bias voltage of 0.5 MV/cm, the dielectric constant and leakage current density of the BSTZ thin films are 191 and 3×10^?8 A/cm², respectively. In addition, under various measured temperatures (0 ～ 80°C) and frequencies (100 kHz ～ 1 MHz), all the dielectric constants remain almost unchanged. Compared to BSTZ thin films reported previously, in this study, the deposited thin films have the advantage of lower leakage current and hence are suitable for the applications of dynamic random access memory.     

Structure,Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba_0.70Ca_0.30TiO₃-(BCT),Ba(Zr_0.2Ti_0.8)O₃-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.     

Multiferroic properties of single-phase perovskite structure 0.8BiFeO<Subscript>3</Subscript>–0.2SrTiO<Subscript>3</Subscript> ceramics synthesized using the Pechini method

Single-phase perovskite structure 0.8BiFeO₃–0.2SrTiO₃ ceramics were synthesized by a modified sol-gel method. According to the scanning electron microscopy results, the grain sizes of as-prepared samples increased obviously as the annealing temperature rose. Compared with pure BiFeO₃, superior multiferroic and dielectric properties were obtained i.e. remnant magnetization M_r?=?0.10 emu/g with a maximum magnetic field of 50 kOe and maximum polarization P_max?=?8.738 μC/cm² with an applied electric field of 50 kV/cm. Furthermore, the volcano-shape evolution of diffraction peaks and maximum magnetization with increasing sintering temperature indicate that appropriate annealing temperature has a remarkable influence on the enhancement of the multiferroic properties and dielectric performance of 0.8BiFeO₃–0.2SrTiO₃ ceramics. The annealing temperature that yields the most favorable multiferroic properties for the 0.8BiFeO₃–0.2SrTiO₃ solid solution ceramic is somewhere close to 1300 K.     

Electroless nano zinc oxide–activate carbon composite supercapacitor electrode

An electroless deposition process was used to synthesize the nanostructured zinc oxide (ZnO)–activated carbon (AC) as supercapacitor. The composite oxide was studied by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction analysis (XRD). The electrochemical performance of the nanocomposite was analyzed through cyclic voltammetry (CV) and AC impedance spectroscopy (EIS) in 0.1 M Na₂SO₄ as electrolyte. A specific capacitance 187 F g^?1 at a scan rate of 5 mV s^?1 was obtained using cyclic voltammetry (CV) and a nearly rectangular shaped CV curve was observed for the composite oxide. The supercapacitor was quite stable during charge–discharge cycling and exhibited constant capacitance during the long-term cycling. It also yielded a specific capacitance 171 F g^?1 at 5 mA cm^?2 with a high energy density of 21.9 Wh kg^?1 and 4.2 kW kg^?1 of power density. Due to unique structure of prepared ZnO–AC nanocomposite, it is a promising candidate for supercapacitor.     

The performance and negative bias illumination stability of Hf-In-Zn-O thin film transistors on sputtering conditions

This study examined the performance and stability of amorphous Hf-In-Zn-O (a-HIZO) thin film transistors (TFTs) with different sputtering conditions (DC and RF) for the active layer. The field-effect mobility and stability under negative bias illumination stress for the DC device significantly improved to 13.7 cm²/Vs and ?1.5 V shift of threshold voltage, respectively, compared to those (2.4 cm²/Vs and ?2.4 V shift) for the RF device. It is suggested that the incorporation of hydrogen into the RF-sputtered HIZO film has generated larger defect states in the vicinity of the HIZO/gate insulator interface, which may act as hole trap centers. This work demonstrates that the oxide TFTs combined with DC magnetron sputtering will be a prominent candidate for commercial production of the TFT backplane toward next-generation display applications.     

Improving the rate performance of LiCoO2 by Zr doping

Zr-doped LiCoO₂ cathode materials for lithium ion batteries were synthesized by an ultrasonic spray pyrolysis method. The synthesized powders with less than 1 mol% Zr had a single phase layered structure while those with 5 mol% Zr had a little secondary phase, Li₂ZrO₃. The cycle stabilities of Zr-doped and undoped LiCoO₂ were compared at various charge–discharge rates. The Zr-doped LiCoO₂ showed much improved cycle stability compared to the undoped, especially at a high C-rate of 3C (4.2 mA/cm²). To investigate the reasons of the improvement, changes of the lattice parameters and the interatomic distances of Co–Co and Co–O of the doped and the undoped powders were analyzed using XRD and EXAFS. The lattice parameters, a and c, increased in the powders with less than 1 mol% Zr, but decreased in the powder with 5 mol% Zr. On the other hand, the interatomic distances of Co–Co and Co–O did not change with Zr doping. From these results, the improved cycle stability is thought to be due to the expanded inter-slab distance, which enhances Li-ion mobility during charge/discharge processes.     

Dielectric and piezoelectric properties of KCT added (Li0.02(Na0.56 K0.46)0.98(Nb0.81Ta0.15Sb0.04)O3 ceramics

In this study, [Li_0.02(Na_0.56 K_0.46)_0.98](Nb_0.81Ta_0.15Sb_0.04)O₃ + x mol% K_5.4Cu_1.3Ta₁₀O₂₉ ceramics were fabricated by conventional solid-state solution processes. Then, their dielectric and piezoelectric properties were investigated. Sinterability of all samples was enhanced because K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) acted as sintering aids. As the result of XRD, phase structure showed orthorhombic symmetry when KCT ≤ 0.2 mol%. Whereas, the phase structure changed from orthorhombic symmetry to tetragonal symmetry when KCT?≥?0.4 mol%. The results suggest that the orthorhombic and tetragonal phases co-exist in the composition ceramics with 0.2 mol% < KCT < 0.4 mol% at room temperature. The effects of the addition of KCT on the dielectric and piezoelectric properties were investigated. As the result, excellent properties of density=4.81[g/cm³], electromechanical coupling factor (k_p)=0.48 and piezoelectric constant(d₃₃)=252[pC/N] were obtained in the composition ceramics with 0.4 mol%KCT.     

Preparation,characterisation, and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoelectric ceramics

Na_0.5?K_0.5NbO₃ (KNN) ceramics were sintered at different temperatures (970 °C, 1000 °C, 1030 °C, 1060 °C, and 1090 °C) for 3 h by a pressureless sintering method. The powders had been synthesised by sol–gel method, using citric acid as a coordination agent and ethylene glycol as an esterifying agent. The effects of temperature on the phase, microstructure, dielectric, ferroelectric, and piezoelectric properties of the as-prepared ceramics were analysed. The results revealed that all of the ceramics had a pure perovskite phase with orthorhombic symmetry. The piezoelectric constant (d ₃₃), the relative dielectric constant (ε _r), the planar electromechanical coupling coefficient (K _p), and the remnant polarization (P _r) initially increased and then decreased with increasing of temperature in such KNN ceramics. The volatilization of sodium and potassium increased with increasing sintering temperature. Over the range of temperatures studied, those ceramics sintered at 1060 °C had the following optimal properties: (ρ?=?3.97 g/cm³, d ₃₃?=?119 pC/N, ε _r?=?362.46, tan δ?=?0.05, K _p?=?0.23, P _r?=?11.97 μC/cm², E _c?=?10.35 kV/cm, and T _c?=?408 °C).