Preparation and electrochemical properties of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by a rheological-phase-assisted microwave synthesis method

By using LiCO₃ and MnO₂, a rheological-phase-assisted microwave synthesis method has been applied in the fast preparation of spinel LiMn₂O₄ in order to reduce the cost of cathode materials. Comparing with the pristine LiMn₂O₄ obtained by the traditional solid-state reaction method, the structure and surface morphology of the samples synthesized by the rheological-phase-assisted microwave synthesis method have been investigated. The powders were used as positive materials for lithium-ion battery, whose charge/discharge properties and cycle performance have been examined in detail. As a result, the powders prepared by the rheologicalphase-assisted microwave synthesis method at 750°C are pure spinel LiMn₂O₄ with regular shapes and uniform distribution, which exhibit higher capacity and much better reversibility than the sample prepared by the traditional solid-state reaction. The text was submitted by the authors in English.     

Superionic Conductors in the Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>-Bi<Subscript>2</Subscript>VO<Subscript>5.5</Subscript> System

Bi₂V_xW_{1 − x} O_{6 − y} ceramics are synthesized, and their structure and electrical properties are studied. The results indicate that the Bi₂WO₆-Bi₂VO_5.5 system contains Bi₂WO₆- and Bi₂VO_5.5-based solid solutions in the ranges 0 < x ≤ 0.2 and 0.75 ≤ x < 1, respectively. Tungsten stabilizes the high-temperature, tetragonal phase γ-Bi₂VO_5.5, which persists down to room temperature at 0.75 ≤ x ≤ 0.84. In the range 350–550°C, the electrical conductivity of the bismuth-vanadate-based solid solutions exceeds that of Bi₂VO_5.5 by about one order of magnitude. The conductivity of the Bi₂WO₆-based solid solutions is also higher than that of the host phase.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 866–870.Original Russian Text Copyright © 2005 by Voronkova, Yanovskii, Kharitonova, Rudnitskaya.     

Effects of different particle sizes on electrochemical performance of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials

Spinel LiMn₂O₄ were prepared by adipic acid-assisted sol–gel method at 800 °C, and the cathode materials with different particle sizes were obtained through ball milling. The effects of different particle sizes on electrochemical performance of LiMn₂O₄ sample were investigated by X-ray diffraction (XRD), galvanostatic charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), respectively. XRD data exhibits that all samples exhibit the same pure spinel phase; EIS and CV indicate that LiMn₂O₄ samples with smaller particle size have higher charge transfer resistance and oxidation potential than that of other samples corresponding to the extraction of Li⁺ ions, respectively; galvanostatic charge–discharge test shows that the particle size has significant effects on the electrochemical performance of spinel LiMn₂O₄ cathode materials.     

Structural,Superconducting, and Magnetic Properties of Y<Subscript>1- <Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript>x</Subscript>Rh<Emphasis Type="Italic">4</Emphasis>B<Emphasis Type="Italic">4</Emphasis> Borides

Samples with nominal compositions Y_1-x Dy_xRh₄B₄ are prepared by argon-atmosphere arc melting. The phase composition of the samples and the elemental compositions of the individual phases present are determined by x-ray diffraction and electron-probe x-ray microanalysis. The results indicate that increasing the dysprosium content of the starting mixture increases the percentage of the magnetic phase and reduces that of the superconducting phase in the samples. The electrical resistivity, magnetic susceptibility, and magnetic moment of the samples are measured between 1.6 and 30 K (magnetic fields of up to 14 T). The magnetic phase present in the samples with 0.2 ≤ × ≤ is shown to undergo ferromagnetic ordering at T _magn ≃ 13–13.5 K. The samples with 0 ≤ × ≤ 0.6 contain a superconducting phase with T _c from 9.1 to 5.0 K. The superconducting and magnetic properties of the Y_0.6Dy_0.4Rh₄B₄ sample are examined in detail.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 676–681.Original Russian Text Copyright © 2005 by Burkhanov, Lachenkov, Kuz’micheva, Kovneristyi, Khlybov, Kostyleva, Tomilin.     

Synthesis and cycling performance of double metal doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials for rechargeable lithium ion batteries

In order to improve the cycling performance of LiMn₂O₄, the spinel phases LiCo_0.15Mn_1.85O₄ and LiCo_0.05M_0.1Mn_1.85O₄ (M = Ni, Zn, Cu) were prepared by the sol-gel method. Their structures have been investigated by x-ray diffraction. Electrochemical studies were carried out using the Li | Li _x Mn₂O₄ (x = 1.05, 1.1), LiCo_0.15Mn_1.85O₄, and LiCo_0.05M_0.1Mn_1.85O₄ (M = Ni, Zn, Cu) cells. The capacity loss of Li | Li _x Mn₂O₄ (x = 1.05, 1.1) cells is about 21.7 and 6.4% after 30 cycles, whereas that for Co, Co-Ni, Co-Zn, and Co-Cu doped spinel materials is about 4.0, 2.0, 1.0, and 1.9%, respectively. The good capacity retention of LiCo_0.05M_0.1Mn_1.85O₄ (M = Ni, Zn, Cu) electrodes is attributed to stabilization of spinel structure by double metal doping for Mn ion sites. Double substituted spinels display better performance in terms of cycle-life compared with LiMn₂O₄. The text was submitted by the authors in English.     

Phase Relations and Transport Properties of Alloys in the Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-TlGaTe<Subscript>2</Subscript> System

Using physicochemical analysis, the Bi₂Te₃-TlGaTe₂ system is shown to contain Bi₂Te³⁻ and TlGaTe₂-based restricted solid-solution series and a liquid-liquid miscibility gap in the composition range ≃12–30 mol % TlGaTe₂. The power factor α²σ of (Bi₂Te₃)_1−x (TlGaTe₂)_x solid solutions with 0.01 ≤ x ≤ 0.02 is suitable for thermoelectric applications.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 785–786.Original Russian Text Copyright © 2005 by Abilov, Seidov.     

Photoluminescence and Electrical Conductivity of As<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Au〉 and As<Subscript>2</Subscript>S<Subscript>5</Subscript>〈Au〉 Glasses

The 77-K photoluminescence spectra of (As₂S₃)_{100 − x} Au_x and (As₂S₅)_{100 −x} Au_x (0 ≤ x ≤ 0.04) semiconducting glasses are measured for the first time. At low doping levels, the spectra of the (As₂S₅)_{100 − x} Au_x glasses are split into two components, one of which arises from the Au dopant. The temperature-dependent conductivity of the glasses shows two breaks at low Au concentrations and anomalous behavior in the range 300–360 K. Qualitative analysis of the conductivity data suggests that most of the impurity atoms have saturated valence bonds and form solid solutions with host atoms, changing the band gap of the material. A small fraction of the impurity atoms, those having unsaturated valence bonds, produce an electrically active level responsible for impurity conduction.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 876–880.Original Russian Text Copyright © 2005 by Babaev, Kamilov, Sultanov, Askhabov, Terukov.     

Nano-domain structure of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> spinel

XRD-pure Li₄Mn₅O₁₂ spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn⁴⁺ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li₄Mn₅O₁₂ reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li₂MnO₃. For Li₄Mn₅O₁₂ compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn⁴⁺ ions having different metal environments: (i) Mn⁴⁺ ions surrounded by Li⁺ and Mn⁴⁺ and (ii) Mn⁴⁺ ions in Mn⁴⁺-rich environment. The composition of the Li⁺, Mn⁴⁺-shell around Mn⁴⁺ mimics the local environment of Mn⁴⁺ in monoclinic Li₂MnO₃, while the Mn⁴⁺-rich environment is related with that of the spinel phase. The structure of XRD-pure Li₄Mn₅O₁₂ comprises nano-domains with a Li₂MnO₃-like and a Li_4/3−x Mn_5/3+x O₄ composition rather than a single spinel phase with Li in tetrahedral and Li_1/3Mn_5/3 in octahedral spinel sites. The annealing of Li₄Mn₅O₁₂ at temperature higher than 600 °C leads to its decomposition into monoclinic Li₂MnO₃ and spinel Li_4/3−x Mn_5/3+x O₄.     

Synthesis of magnetic nanocomposite MgO/MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> from Mg-Fe layered double hydroxides precursors

The present letter reported the synthesis of MgO-containing magnetic nanocomposites by calcinations of tailored hydrotalcite-like layered double hydroxides (LDHs) of the type [Mg_{1 – x – y}Fe²⁺_yFe^{3 +}_x(OH)₂]^{x +}(A)_x/2·mH₂O (y 0; A = CO₃^{2 –} or SO₄^{2 –}) precursors at 900°C for 2 h. The results indicate that calcination of LDHs gives rise to the formation of magnetic nanocomposites of MgO and MgFe₂O₄ spinel ferrite, where MgO formed could disperse and separate MgFe₂O₄ particles, and MgO itself was also dispersed or embedded uniformly in the MgFe₂O₄ spinel matrix. Furthermore, initial studies on the bactericidal properties with staphylococcus aureus show that these as-synthesized nanometer-sized materials have significant bactericidal effect, which increases with the increasing volume fraction of MgO.     

Sol-Gel Synthesis and Photoluminescence of RE<Subscript>x</Subscript>Lu<Subscript>2-<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> (RE = Y,Gd) Nanophosphors

RE_xLu_2-x O₃:Eu³⁺ (RE = Y, Gd) nanophosphors with x = 0.4, 1.0, and 1.6 were synthesized using rare-earth salicylate coordination polymers as precursors for the luminescent species RE_xLu_2-x O₃:Eu³⁺ (RE = Y, Gd) composed of polyethylene glycol both as a dispersing medium and fuel. Their particle sizes were around 100 nm as determined by scanning electron microscopy and x-ray diffraction.__________From Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 706–710.Original English Text Copyright © 2005 by Zhou, Yan.This article was submitted by the authors in English.     

Ionic Conductivity of Ln<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>7 − <Emphasis Type="Italic">x</Emphasis>/2</Subscript> (Ln = Sm-Gd) Solid Solutions

The electrical conductivity of Ln_{2 + x} Zr_{2 − x} O_{7 − x/2} (Ln = Sm-Gd) solid solutions prepared from mechanically activated Ln₂O₃ and ZrO₂ is shown to correlate with their structural properties. In the three systems, the x-T regions are determined in which electrical transport is dominated by oxygen-ion conduction. In the Sm₂O₃-ZrO₂ system, ionic conductivities from 5 × 10⁻⁴ to 6 × 10⁻³ S/cm at 740°C are found in Sm_{2 + x} Zr_{2 − x} O_{7 − x/2} with 26.6, 33.3, 35.5, 37, and 40 mol % Sm₂O₃ prepared at 1450, 1530, and 1600°C. Eu_{2 + x} Zr_{2 − x} O_{7 − x/2} and Gd_{2 + x} Zr_{2 − x} O_{7 − x/2} containing 33.3 to 37 mol % Ln₂O₃ have 740°C ionic conductivities of 10⁻³ to ∼7.5 × 10⁻³ and 10⁻³ to 7 × 10⁻³ S/cm, respectively. The activation energy of conduction in Ln_{2 + x} Zr_{2 − x} O_{7 − x/2} (Ln = Sm-Gd), E _a = 0.84–1.04 eV, increases with the atomic number of Ln and x. The highest ionic conductivity is offered by the stoichiometric Ln₂Zr₂O₇ (Ln = Sm-Gd) pyrochlores prepared at 1600°C, owing to the optimal concentration of Ln_Zr + Zr_Ln antistructure pairs (∼5–22%). The grains in the ceramic samples studied range in size from 0.5 to 2 µm.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 975–984.Original Russian Text Copyright © 2005 by Shlyakhtina, Kolbanev, Knotko, Boguslavskii, Stefanovich, Karyagina, Shcherbakova.     

Microstructure and magnetic properties of Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by combustion reaction

An investigation was made of samples having a chemical formula of Ni_1−x Zn _x Fe₂O₄, where x = 0.3, 0.5 and 0.7. The samples were prepared by the reaction combustion synthesis method and sintered at 1,200 °C/2 h in a static air atmosphere. The influence of the Zn concentration on the relative density, microstructure and magnetic properties of the samples was studied. X-ray diffraction, scanning electron microscopy and magnetic hysteresis loop tracer were used to analyze the compositions. The samples were found to have a spinel cubic structure, sintered density of 92.9%–98.8% of the corresponding X-ray density, homogeneous microstructure with grain size ranging from 1.37 to 3.36 μm, maximum flux density of 0.16–0.35 T, field coercivity ranging from 17 to 168 A/m, and loss hysteresis of 1.5–105 W/kg. Increased grain growth, with fine pores inside the grains, was found to occur as the Zn concentration increased. The overall findings are discussed here in light of the existing understanding of these systems.     

Relaxor behavior and ferroelectric properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-KNbO<Subscript>3</Subscript> lead-free ceramics

Lead-free ferroelectric ceramics of (1−x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃]-x KNbO₃(x = 0, 0.02, 0.04, and 0.06) were prepared by the conventional ceramic fabrication technique. The crystal structure, dielectric properties and P-E hysteresis loops were investigated. XRD data showed that all compositions could form pure perovskite structure. Temperature dependence of dielectric constant ε _r and dissipation factor tanδ measurement between room temperature and 500^∘C revealed that the compounds experience phase transitions that from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric in the range of x = 0–0.04. The frequency dependent dielectric constant showed these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant and dissipation factor increased sharply attributed to the superparaelectric clusters after the KNbO₃ doped.     

Effect of nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on formation and superconductivity of bulk MgB<Subscript>2</Subscript>

Bulk materials of MgB₂ have been prepared with the stoichiometry of MgB₂(Al₂O₃) _x (x = 0, 2, 5, 10 and 20% nano-Al₂O₃ powders), by using solid-state reaction route. All samples were sintered at 750 °C for 30 min in a calorimeter to monitor the sintering reaction process. It is found that the onset temperatures of reaction between Mg and B powders increase significantly with increasing the amount of Al₂O₃. However, the reaction time is shortened for the nano-Al₂O₃ powders can effectively activate the reaction as a catalyst. The critical transition temperature decreases from 38.5 to 31.6 K, and the corresponding temperature window becomes narrow (less than 2.6 K). Furthermore, the amount of MgO impurity was found to increase with the increase of Al₂O₃, which probably indicates that partial Mg was replaced by Al.     

Synthesis and electrochemical properties of Indium doped spinel LiMn2O4

In this paper, spinel LiMn_2–x In _x O₄ powder were prepared by rheological phase reaction method with the CH₃COOLi·2H₂O, (CH₃CO₂)₂Mn·4H₂O, and In₂O₃. The structures were characterized by X-ray diffraction and the electrochemical cycling performance were also observed. The results showed that the spinel LiMn_2–x In _x O₄ were pure phase with very excellent performance. As a cathode material for lithium secondary batteries, LiMn_1.98In₂O₄ had a high initial discharge-capacity with 132.42 mAh/g and a good cyclic reversibility with 98.9%. Even after 60 cycles, the discharge capacity still kept 126.29 mAh/g.     

In Situ X-ray Diffraction Study of the Phase Transition of Nanocrystalline In(OH)<Subscript>3</Subscript> to In<Subscript>2</Subscript>O<Subscript>3</Subscript>

Single-crystalline indium oxide (In₂O₃) nanocubes were successfully prepared via dehydration of indium hydroxide (In(OH)₃) nanocubes synthesized by a hydrothermal method. In situ x-ray diffraction patterns of the phase transition were obtained. Transmission electron microscopy indicated that the morphology of the In₂O₃ nanocrystallites was the same as that of their precursors, In(OH)₃ nanocrystallites. The reported method, the dehydration of In(OH)₃ nanocrystallites prepared by a hydrothermal method, shows a simple and effective synthesis route for In₂O₃ nanostructured materials.__________From Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 702–705.Original English Text Copyright © 2005 by Hongliang Zhu, Naiyan Wang, Lina Wang, Kuihong Yao, Xiaofei Shen.This article was submitted by the authors in English.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

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.     

Structural changes induced by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> addition in strontium-borate glass matrix

Glasses of the xFe₂O₃·(100−x)[B₂O₃·SrO] system, with 0 ≤ x ≤ 30 mol% were studied by X-ray diffraction, density, optical microscopy and FT-IR spectroscopy measurements. The X-ray patterns for the prepared system show that vitreous phase is present only in the sample with x < 40 mol%. For x ≥ 40 mol% in the studied samples is evidenced crystalline phase of Fe₂O₃. SEM measurements for the sample with x = 40 mol% shows that there are formed Fe₂O₃ microcrystallites with 10–20 μm dimension. FT-IR spectroscopy measurements shown that BO₃ and BO₄ are the main structural units of the glass system and the iron ions are located in the glass network.     

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.