Facile synthesis and electrochemical properties of layered Li[Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>]O<Subscript>2</Subscript> as cathode materials for lithium-ion batteries

A layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ was synthesized by an oxalate co-precipitation method. The morphology, structural and composition of the as-papered samples synthesized at different calcination temperatures were investigated. The results indicate that calcination temperature of the sample at 850°C can improve the integrity of structural significantly. The effect of calcination temperature varying from 750°C to 950°C on the electrochemical performance of Li[Ni_1/3Mn_1/3Co_1/3]O₂, cathode material of lithiumion batteries, has been investigated. The results show that Li[Ni_1/3Mn_1/3Co_1/3]O₂ calcined at 850°C possesses a higher capacity retention and better rate capability than other samples. The reversible capacity is up to 178.6 mA?h?g^-1, and the discharge capacity still remains 176.3 mA?h?g^-1 after 30 cycles. Moreover, our strategy provides a simple and highly versatile route in fabricating cathode materials for lithium-ion batteries.     

Preparation and phase formation of perovskite Pb(Ni<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> by a reaction-sintering process

Pyrochlore-free Pb(Ni_1/3Nb_2/3)O₃ perovskite ceramics produced by a simple and effective reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Ni(NO₃)₂ and Nb₂O₅ was pressed and sintered directly into PNN ceramics. Density of 98.5% of theoretical value was obtained after sintered at 1230 °C for 2 h in air. 99.3% of theoretical density was obtained after sintered at 1,200 °C for 2 h in PbO compensated atmosphere. PNN ceramic with dielectric constant 1,680 at 25 °C and 1 kHz has been obtained.     

Dielectric relaxation phenomena in the compound: LiCo<Subscript>3/5</Subscript>Mn<Subscript>1/5</Subscript>Cu<Subscript>1/5</Subscript>VO<Subscript>4</Subscript>

Solution-based chemical method has been used to produce LiCo_3/5Mn_1/5Cu_1/5VO₄ ceramics. The formation of the compound is checked by X-ray diffraction analysis and it reveals an orthorhombic unit cell structure with lattice parameters of a = 9.8262 Å, b = 3.0706 Å, c = 14.0789 Å. Field emission scanning electron micrograph indicates a polycrystalline texture of the material with grains of unequal sizes (~0.2 to 3 μm). Complex impedance spectroscopy technique is used to study the dielectric properties. Temperature dependence of dielectric constant (ε _r) at various frequencies exhibits the dielectric anomalies in ε _r at T _c (transition temperature) = 245, 255, 260 and 265 °C with (ε_r)_max. ~458, 311, 214 and 139 for 50, 100, 200 and 500 kHz, respectively. Frequency dependence of tangent loss at various temperatures shows the presence of dielectric relaxation in the material.     

A facile method to enhance electrochemical performance of high-nickel cathode material Li(Ni<Subscript>0.8</Subscript>Co<Subscript>0.1</Subscript>Mn<Subscript>0.1</Subscript>)O<Subscript>2</Subscript> via Ti doping

The cycle stability of Li(Ni_0.8Co_0.1Mn_0.1)O₂ is enhanced obviously by titanium doping via a facile solid-state method. The property of crystal structure is evaluated by XRD, which illustrates the samples possessed a layered α-NaFeO₂ structure with R-3m space group. According to the charge/discharge studies, the capacity retention of pristine sample is around 51% after 125 cycles at 5 C, and the sample with Ti dopant displays a good cyclic stability, after 125 cycles, the capacity retention increases to 75% under 5 C, suggesting it could be possibly applied in fast charge Lithium-ion battery area. The superb electrochemical performance might be attributed to the Ti⁴⁺ occupy the layer structure to broaden the Lithium-ion channel, which is benefit to lithium intercalation and deintercalation during cycling.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Dielectric,humidity behavior and conductivity mechanism of Mn<Subscript>0.2</Subscript>Ni<Subscript>0.3</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrite prepared by co-precipitation method

Mn–Ni–Zn ferrite with the chemical formula of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ was prepared by co-precipitation method. The X-ray diffraction (XRD) results show that the prepared sample crystallizes in the cubic spinel structure with the space group of Fm3m. The morphological analysis of the sample was investigated by scanning electron microscopy (SEM). The dielectric properties of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ ferrite were studied in a frequency range from 20 Hz to 10 MHz and at a temperature range from 293 to 733 K. The dielectric constant decreases with the increasing frequency for all the temperature values chosen. The AC conductivity mechanism was found the small polaron type of conductivity, and in addition to that, the DC conductivity can be explained by Arrhenius type conductivity. According to the dielectric results, relaxation process fits Cole–Cole model. Finally, the effect of the relative humidity upon the impedance of the sample was discussed for a frequency range between 20 Hz and 10 MHz. It is found that the impedance values decrease almost linearly with the increasing % RH (relative humidity) values at low frequencies, while the impedance of the sample is independent of % RH at high frequencies.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>/worm-like mesoporous carbon synthesized via a microwave method for supercapacitors

A quick and facile microwave method has been employed to prepare Mn₃O₄/worm-like mesoporous carbon (Mn₃O₄–MC) composites. Structural and morphological characterizations of worm-like mesoporous carbon and Mn₃O₄–MC composites have been carried out using X-ray diffraction, transmission electron microscopy, N₂ adsorption–desorption, and electrochemical measurement. Cyclic voltammograms demonstrate that the Mn₃O₄–MC composites perform improved capacitive behavior at the range of −0.8~0.2 V (vs. Hg/HgO electrode) with reversibility. The Mn₃O₄–MC composite electrode possesses an enhanced specific capacitance of 266 F g⁻¹ at a sweep rate of 1 mV s⁻¹.     

Dielectric properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Sm(Co<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics at microwave frequency

The microwave dielectric properties and the microstructures of Sm(Co_1/2Ti_1/2)O₃ ceramics with B₂O₃ additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of Sm(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. It is found that Sm(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B₂O₃ addition. At 1,290 °C, Sm(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% B₂O₃ addition possess a dielectric constant (ε _r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of −11.4 ppm/ °C. The B₂O₃-doped Sm(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Microstructure and H<Subscript>2</Subscript>S gas sensing properties of nanocrystalline perovskite-type La<Subscript>0.6</Subscript>Co<Subscript>0.4</Subscript>Mn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>3</Subscript>

Nanocrystalline La_1−x Co _x Mn_1−y Ni _y O₃ (x = 0.2 and 0.4; y = 0.1, 0.3, and 0.5) thick films sensors prepared by sol–gel method were studied for their H₂S gas sensitivity. The structural and morphological properties have been carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Average particle size estimated from XRD and TEM analyses was observed to be 30–35 nm. The gas response characteristics were found to depend on the dopants concentration and operating temperature. The maximum H₂S gas response of pure LaMnO₃ was found to be at 300 °C. In order to improve the gas response, material doped with transition metals Co and Ni on A- and B-site, respectively. The La_0.6Co_0.4Mn_0.5Ni_0.5O₃ shows high response towards H₂S gas at an operating temperature 250 °C. The Pd-doped La_0.6Co_0.4Mn_0.5Ni_0.5O₃ sensor was found to be highly sensitive to H₂S at an operating temperature 200 °C. The gas response, selectivity, response time and recovery time were studied and discussed.     

Phase developments in Pb(Mg<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> and Pb(Zn<Subscript>1/2</Subscript>W<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> via B-site precursor route

Phase formation stages of MgWO₄ and ZnWO₄ (precursor compositions for following steps) were investigated by monitoring the reactions of oxide chemicals at various temperatures. Developed phases were examined by using X-ray diffraction (XRD). Successive attempts were also conducted for Pb(Mg_1/2W_1/2)O₃ (PMW) and Pb(Zn_1/2W_1/2)O₃ (PZW) by reacting PbO with the precursor compounds. Stages of phase development in the two compositions were also analyzed. The results are compared with those of another tungsten-containing perovskite Pb(Fe_2/3W_1/3)O₃ (PFW) and its B-site precursor Fe₂WO₆. After PbO addition to the precursor powders, a perovskite phase formed directly (i.e., without any intermediate phases) in the case of PMW. For PbO + ½ZnWO₄, in contrast, the decomposition of ZnWO₄ and preferential reaction with PbO resulted in Pb₂WO₅ and ZnO, instead of the perovskite PZW.     

Magnetic properties of Er<Subscript>2</Subscript>Mn<Subscript>2/3</Subscript>Re<Subscript>4/3</Subscript>O<Subscript>7</Subscript>, a new zirkelite-structure oxide

We have studied the magnetic properties of the new compound Er₂Mn_2/3Re_4/3O₇ prepared by reacting Er₃ReO₈, ReO₂, MnO, and metallic Re at 1020°C in silica tubes sealed off under vacuum. The compound is shown to have the zirkelite structure with hexagonal cell parameters a = 7.3174(6) Å and c = 17.365(1) Å (sp. gr. P3₁21₁, Z = 6). Magnetization data obtained in the range 2–300 K demonstrate that, above ～150 K, its magnetic susceptibility exhibits Curie-Weiss behavior with an effective magnetic moment of 9.50μ_B. Dynamic magnetic susceptibility measurements point to spin-glass behavior of this compound at low temperatures.     

Synthesis and characterization of ternary compound,Mn<Subscript>2</Subscript>SnTe<Subscript>4</Subscript>

Mn₂SnTe₄ was synthesized by direct fusion using the anneal method. X-ray powder diffraction analysis indicated that this material crystallizes in the olivine-type structure, space group Pnma, Z = 4, with unit cell parameters: a = 14.020(2) Å, b = 8.147(1) Å, c = 6.607(1) Å, V = 754.7(2) ų. The Rietveld refinement converged to the figures of merit, R _p = 6.9%, R _wp = 8.5%, R _exp = 6.0%, χ² = 2.0 and S = 1.4.     

Preparation of Pb(Zr,Ti)O<Subscript>3</Subscript>–Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by dry–dry method

Ternary perovskite ceramics of Pb[(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x]_0.98Nb_0.02O_3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x ]_0.98Nb_0.02O_2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase solid solution with ZrTiO₄ structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric ceramics.     

Synthesis and characterization of pseudo-ternary Pb(Fe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ferroelectric ceramics via a B-site oxide mixing route

Perovskite phase formation and dielectric/ferroelectric properties of the pseudo-ternary Pb(Fe_1/2Nb_1/2)O₃-PbZrO₃-PbTiO₃ (PFN-PZ-PT) ferroelectric ceramics have been investigated as promising materials for multi-layer ceramic capacitors. Complete solid solution with pure perovskite phase can be formed in this system in the whole composition range studied using conventional solid-state reaction method via a B-site oxide mixing route. Crystal lattice of the ceramics obtained shrinkages with the increase of the concentration of Pb(Fe_1/2Nb_1/2)O₃ (PFN) and expands with the increase of the content of PbZrO₃ (PZ). With the increase of the concentration of PbTiO₃ (PT), crystal structure of PFN-PZ-PT changes from pseudo-cubic ferroelectric phase to tetragonal one while retains the fraction of PFN as constant. A morphotropic phase boundary (MPB) forms at the composition of 42 mol% PT regardless of whatever concentration of PFN, and the content of PFN affects little on the composition of MPB. The preliminary phase diagram of the PFN-PZ-PT system is determined by X-ray diffraction (XRD) measurements combining with dielectric/ferroelectric characterization. Dielectric measurements indicate that the value of dielectric maximum (ɛ_m) and the temperature where ɛ_m appears (T_m) increase with the increase of the concentration of PT. However, PFN exhibits opposite effects, i.e., ɛ_m increases with the increase of the concentration of PFN accompanied by the decrease of T_m.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Thermal Expansion of Ni<Subscript>3</Subscript>S<Subscript>2</Subscript> in Ni<Subscript>3</Subscript>S<Subscript>2</Subscript>-Ni Alloys

The thermal expansion of nickel sulfide in Ni₃S₂-Ni alloys (a sample synthesized in this work and a commercial Ni₃S₂-Ni-Cu₉S₅ converter matte) is measured using high-temperature x-ray diffraction. The best fit equations are derived for the temperature-dependent (≤980 K) parameters of the rhombohedral (hexagonal) and cubic cells of nickel sulfide, and the thermal expansion coefficients of Ni₃S₂ are determined. The results demonstrate that the thermal expansion of Ni₃S₂ is influenced by impurity phases: Ni metal and Cu₉S₅. The chemical strain arising from the dissolution of the copper sulfide in Ni₃S₂ cancels out the shear strain near the polymorphic transformation.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 1005–1010.Original Russian Text Copyright ¢ 2005 by Vershinin, Selivanov, Gulyaeva, Sel’menskikh.     

Properties of fluorine-doped PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> ceramics

We report the first fluorine doping of lead magnesium niobate in the PbMg _{(1 + x)/3}Nb_{(2 ? x)/3}O_{3 ? x} F _x system in a wide composition range, x = 0.025 to 0.625. The fluorine content of the samples is shown to be substantially lower than the intended one because of the fluorine volatilization in the form of HF during synthesis and sintering in air. The ceramics consist of magnesium and lead oxides undetectable by x-ray diffraction, and a perovskite phase whose composition can be represented by the formula PbMg_{(1 + m)/3}Nb_{(2 ? m)/3}O_{3 ? m} F _m , where the fluorine content after sintering is m ≤ 0.12. The PbO and MgO contents of the ceramics depend on the starting mixture composition (x) and heat-treatment conditions (hydrogen fluoride and lead oxide volatilization). As a result of the low fluorine content, the diffraction patterns of the samples show no superlattice reflections, and their lattice parameter varies insignificantly with x. Data are presented on the temperaturedependent dielectric permittivity of ceramic samples sintered and annealed under different conditions.     

Fabrication of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite nanofibers by electrospinning

PVA(Polyvinyl alcohol)/chromium nitrate/aluminum nitrate composite nanofibers were prepared by using sol–gel processing and electrospinning technique. By high temperature calcinating the above precursor fibers, Cr₂O₃/Al₂O₃ composite nanofibers were successfully obtained. The fibers were characterized by XRD, IR, and SEM, respectively. The results showed that the crystalline phase and the morphology of the fibers depended on the calcination temperatures.     

Seed-assisted sol–gel synthesis and characterization of nanoparticular V<Subscript>2</Subscript>O<Subscript>5</Subscript>/anatase

Nanoparticular supported vanadia materials with crystalline anatase support with a narrow size distribution around 12 nm have been synthesized by a new facile sol–gel, co-precipitation method using decomposable ammonium chloride seed crystals. The materials have been characterized by means of X-ray powder diffraction, transmission electron microscopy and nitrogen physisorption. The synthesized high-surface area anatase particles allowed a loading of up to 15 wt.% vanadia without exceeding monolayer coverage of V₂O₅ in contrast to typical analogous industrial catalysts which only can accommodate 3–5 wt.% vanadia. These materials are promising candidates for improved catalysts for, e.g., oxidation reactions and selective catalytic reduction of NO _X in flue gases.