A high-voltage lithium-ion battery prepared using a Sn-decorated reduced graphene oxide anode and a LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

This paper describes the preparation and characterization of a high-voltage lithium-ion battery based on Sn-decorated reduced graphene oxide and LiNi_0.5Mn_1.5O₄ as the anode and cathode active materials, respectively. The Sn-decorated reduced graphene oxide is prepared using a microwave-assisted hydrothermal synthesis method followed by reduction at high temperature of a mixture of (C₆H₅)₂SnCl₂ and graphene oxide. The so-obtained anode material is characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and electron diffraction spectroscopy. The LiNi_0.5Mn_1.5O₄ is a commercially available product. The two materials are used to prepare composite electrodes, and their electrochemical properties are investigated by galvanostatic charge/discharge cycles at various current densities in lithium cells. The electrodes are then used to assemble a high-voltage lithium-ion cell, and the cell is tested to evaluate its performance as a function of discharge rate and cycle number.     

Investigation of ion transport in Li<Subscript>8</Subscript>ZrO<Subscript>6</Subscript> and Li<Subscript>6</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> solid electrolytes

Lithium ionic conductivity and spin-lattice relaxation rates were measured in Li₈ZrO₆ and Li₆Zr₂O₇ solid electrolytes. It was found that the Li₈ZrO₆ solid electrolyte undergoes a transition to the superionic state in the temperature range 673–703 K. It was shown that Li⁺ ions are mobile in particular lattice positions of the Li₆Zr₂O₇ phase, and that ionic conductivity is monotonic at an activation energy of 79.4 kJ/mol.     

Long-range magnetic order in quasi-one-dimensional NaCrSi<Subscript>2</Subscript>O<Subscript>6</Subscript> and NaCrGe<Subscript>2</Subscript>O<Subscript>6</Subscript> metal oxides

Formation of a long-range magnetic order is observed at low temperatures in NaCrSi₂O₆ and NaCrGe₂O₆ quasi-one-dimensional metal oxide compounds with a pyroxene structure. The first of these compounds, NaCrSi₂O₆, is an antiferromagnet with the Néel temperature T _N =3 K, while the second, NaCrGe₂O₆, is a ferromagnet with the Curie temperature T _C =6 K. From the measurements of magnetization and specific heat of these compounds, the main parameters of their magnetic subsystems are determined. In NaCrSi₂O₆, a spin-flip transition is observed. A change in the type of magnetic order that accompanies the replacement of Si by Ge can be attributed to a change in the parameters of the competing direct antiferromagnetic Cr-Cr and indirect ferromagnetic Cr-O-Cr interactions in isolated chains of CrO₆ octahedra.     

Operational characteristics and power scaling of a transverse flow transversely excited CW CO<Subscript>2</Subscript> laser

Transverse flow transversely excited (TFTE) CO₂ lasers are easily scalable to multikilowatt level. The laser power can be scaled up by increasing the volumetric gas flow and discharge volume. It was observed in a TFTE CW CO₂ laser having single row of pins as an anode and tubular cathode that the laser power was not increasing when the discharge volume and the gas volumetric flow were increased by increasing the electrode separation keeping the gas flow velocity constant. The discharge voltage too remained almost constant with the change of electrode separation at the same gas flow velocity. This necessitated revision of the scaling laws for designing this type of high power CO₂ laser. Experimental results of laser performance for different electrode separations are discussed and the modifications in the scaling laws are presented.     

Resistive switching in β-SrV<Subscript>6</Subscript>O<Subscript>15</Subscript>

We investigate the pressure and temperature behavior of current-dependent resistivity of β-SrV₆O₁₅. We observe a switching between states of different resistivities in the insulating state of β-SrV₆O₁₅. In the low pressure phase, the resistive switching appears at temperatures below the semiconductor-insulator transition. In the high pressure phase, under ~1.6 GPa, the switching appears in the temperature range of the phase transition. The existence of switching may imply an important role of strontium off-stoichiometry for the electrical transport in β-SrV₆O₁₅. No electric-field-induced enhancement of the conductivity is observed. However, the conduction is significantly nonlinear under ~1.6 GPa, indicating that the charge order pattern in the high pressure phase is considerably different from that of the low pressure phase.     

Probing the isomer,fluorination and bond effects in C<Subscript>3</Subscript>H<Subscript>6</Subscript>, cyclo-C<Subscript>3</Subscript>H<Subscript>6</Subscript> and C<Subscript>3</Subscript>F<Subscript>6</Subscript> molecules using electron impact

We have carried out experimental and theoretical studies on electron scattering from the C₃H₆ isomers and C₃F₆ molecules and we report on total, differential as well as theoretical integral elastic cross-sections for these molecules. Vibrational excitation functions are also presented for the typical vibrational peaks in C₃H₆ and cyclo-C₃H₆ for the angle of 90^○, impact energy range of 1–16 eV and loss energies of 0.12 eV and 0.13 eV, respectively. In the cross-sections, clear differences in peak positions and magnitudes between the C₃H₆ isomers can be viewed as the isomer effect. The same is observed between C₃H₆ and C₃F₆ in a clear manifestation of the fluorination effect. The resemblance of the π^* shape resonance in the cross-sections, observed at about 2.2 eV for C₃H₆ and 3.5 eV for C₃F₆, to those in C₂H₄ and C₂F₄ clearly points to the effect of the double bond in the molecular structures for these molecules. Theoretical analysis is performed to provide rationales for the scattering dynamics.     

A lithium salt additive Li<Subscript>2</Subscript>ZrF<Subscript>6</Subscript> for enhancing the electrochemical performance of high-voltage LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

In this work, Li₂ZrF₆, a lithium salt additive, is reported to improve the interface stability of LiNi_0.5Mn_1.5O₄ (LNMO)/electrolyte interface under high voltage (4.9 V vs Li/Li⁺). Li₂ZrF₆ is an effective additive to serve as an in situ surface coating material for high-voltage LNMO half cells. A protective SEI layer is formed on the electrode surface due to the involvement of Li₂ZrF₆ during the formation of SEI layer. Charge/discharge tests show that 0.15 mol L^?1 Li₂ZrF₆ is the optimal concentration for the LiNi_0.5Mn_1.5O₄ electrode and it can improve the cycling performance and rate property of LNMO/Li half cells. The results obtained by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) demonstrate that Li₂ZrF₆ can facilitate the formation of a thin, uniform, and stable solid electrolyte interface (SEI) layer. This layer inhibits the oxidation decomposition of the electrolyte and suppresses the dissolution of the cathode materials, resulting in improved electrochemical performances.     

Optical phonons in Rb<Subscript>2</Subscript>TeBr<Subscript>6</Subscript> and Cs<Subscript>2</Subscript>TeBr<Subscript>6</Subscript> crystals

Raman scattering in Rb₂TeBr₆ and Cs₂TeBr₆ crystals is studied. The phonon spectra of the crystals are calculated using the factor group method. The number of Raman-active modes, their symmetries, and selection rules are found. Observed Raman spectrum lines are identified with atomic vibration modes of the crystal.     

Electrochemical behavior of carbonic precursor with Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>nanostructured material in hybrid battery system

The nanostructured Na₃V₂(PO₄)₃ (NVP) cathode material has been synthesized using the sol-gel route for different molar fractions of citric acid as a carbon source during the synthesis. The nanostructured NVP as cores with carbonic shell structures are fabricated with two different citric acid molar ratios. The thermal treatment has been optimized to convert the amorphous carbon shell into graphitic carbon to realize the better electrical conductivity and thus effective electron transfer during the electrochemical charge transfer process. The X-ray diffraction measurements confirmed the rhombohedral crystallographic phase (space group R-3c) with average crystallite size ~28 ± 5 nm. The coin cells are assembled in a hybrid rechargeable electrochemical cell configuration with lithium as a counter electrode and LiPF₆-EC:DEC:DMC (1:1:1 ratio) as the electrolyte. The electrochemical charge/discharge measurements are carried out at C/10 and C/20 rates and the measured specific capacities are 80 and 120 mAhg^?1 for samples with lower and higher citric acid molar ratios, respectively. The studies suggest that NVP can be used as an effective cathode material in hybrid electrochemical cells, and a higher concentration of citric acid may result in the effective carbonic shell for optimal electron transfer and thus enhanced electrochemical performance.     

Improvement of electrochemical performance for AlF<Subscript>3</Subscript>-coated Li<Subscript>1.3</Subscript>Mn<Subscript>4/6</Subscript>Ni<Subscript>1/6</Subscript>Co<Subscript>1/6</Subscript>O<Subscript>2.40</Subscript> cathode materials for Li-ion batteries

Li-rich layered-layered-Spinel structure spherical Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 particles was successfully prepared and coated with a uniform layer by a two-step co-precipitation method and evaluated in lithium cells. The structures and electrochemical properties of pristine Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 and AlF₃-coated Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 were characterized. When the coating amount was 2 wt%, the cathode showed the best cycling performance and rate capability compared to others. The AlF₃-coated Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 Li-ion cell cathode had a capacity retention of 90.07 % after 50 cycles at 0.5 C over 2.0–4.8 V, while the pristine Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 exhibited capacity retention of only 80.73 %. Moreover, the rate capability and cyclic performance also improved. Electrochemical impedance spectroscopy testing revealed that the improved electrochemical performance might attribute to the AlF₃ coating layer which can suppress the increase of impedance during the charging and discharging process by preventing direct contact between the highly delithiated active material and electrolyte.     

AlF<Subscript>3</Subscript> coating of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> for high-performance Li-ion batteries

AlF₃-coating is attempted to improve the performance of LiNi_0.5Mn_1.5O₄ cathode materials for Li-ion batteries. The prepared powders are characterized by scanning electron microscope, powder X-ray diffraction, charge/discharge, and impedance. The coated LiNi_0.5Mn_1.5O₄ samples show higher discharge capacity, better rate capability, and higher capacity retention than the uncoated samples. Among the coated samples, 1.0 mol% AlF₃-coated sample shows highest capacity after charge–discharged at 30 mA/g for 3 cycles, but 4.0 mol% coated sample exhibits the highest capacity and cycling stability when cycled at high rate of 150 and 300 mA/g. The 40th cycle discharge capacity at 300 mA/g current still remains 114.8 mAh/g for 4.0 mol% AlF₃-coated LiNi_0.5Mn_1.5O₄, while only 84.3 mAh/g for the uncoated sample.     

Dielectric properties of thin ferroelectric Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> films deposited by thermal evaporation

The structure, microstructure, and temperature and field dependences of the dielectric properties of thin (0.5–8.0μm) Sn₂P₂S₆ ferroelectric films deposited onto glass and aluminum foil substrates by thermal vacuum evaporation in a quasi-closed volume are studied. The film-thickness and frequency dependences of the dielectric properties and the unipolarity of the C–V characteristics are explained by the presence of near-surface Schottky-type barrier layers.     

Influence of co-precipitation temperature on microstructure and electrochemical properties of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript> cathode materials for lithium ion batteries

The layered Li-rich Mn-based cathode materials Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ were prepared by using co-precipitation technique at different temperatures, and their crystal microstructure and particle morphology were observed and analyzed by XRD and SEM. The electrochemical properties of these samples were investigated by using charge-discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results indicated that all samples are of high purity. When the precursors were co-precipitated at 50 °C, their cathode materials have the most uniform and full particles and exhibit the highest initial discharge capacity (289.4 mAh/g at 0.1C), the best cycle stability (capacity retention rate of 91.2 % after 100 cycles at 0.5C), and the best rate performance. The EIS results show that the lower charge transfer resistance of 50 °C sample is responsible for its superior discharge capacity and rate performance.     

Luminescence characteristics of the Pr<Superscript>3+</Superscript> ion in SrB<Subscript>4</Subscript>O<Subscript>7</Subscript> and SrB<Subscript>6</Subscript>O<Subscript>10</Subscript>

Spectral and kinetic characteristics of the luminescence and luminescence excitation spectra of polycrystalline SrB₄O₇:Pr (1%) and SrB₆O₁₀:Pr (1%) samples are studied at 150–170 K. The samples show an intense luminescence band in the vicinity of 405 nm (¹ S ₀→¹ I ₆ transitions of Pr³⁺) and shorter wavelength bands also assigned to transitions from the ¹ S ₀ level. The main luminescence decay constant is ～2×10^?7 s. The excitation spectra of the ¹ S ₀ luminescence in these crystals are significantly different. The SrB₄O₇:Pr crystal shows three well-resolved bands at 6.14, 6.55, and 6.91 eV in the region of the 4f ²→4f ¹5d transitions and a complex structure in the region of interband transitions (7.1–20 eV), whereas the SrB₆O₁₀:Pr crystal shows a weakly structured band at 6.31 eV and no excitation in the region of the interband transitions. The physical mechanisms that may be responsible for the observed features of the spectra are discussed.     

Influence of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> on dielectric and barrier properties of polymer

Polymer composite comprising polyvinylidene fluoride (PVDF) and potassium hexatitante (K₂Ti₆O₁₃) was synthesized by solution casting. The effect of K₂Ti₆O₁₃ on surface, thermal, and electrical properties of polymer composite were investigated. The addition of K₂Ti₆O₁₃ with polymer leads to thermal degradation and transition of polymer composite from semi-crystalline to amorphous phase. The optimum results of contact angle for different loading wt% of K₂Ti₆O₁₃ were directly correlated with the surface morphology. Our experimental results confirmed the incorporation of K₂Ti₆O₁₃ in polymer by SEM micrographs. The evaluated dielectric properties (ε' = 424; tan δ = 2.14 at 130 °C and 100 Hz frequency for 20 wt% loading of K₂Ti₆O₁₃) for polymer composite are higher in compared to pure polymer. The enhancement in dielectric constant and changing the surface properties of polymer composite can be used for the development of electrochemical storage device applications.     

Superconductivity in Ti-doped iron-arsenide compound Sr<Subscript>4</Subscript>Cr<Subscript>0.8</Subscript>Ti<Subscript>1.2</Subscript>O<Subscript>6</Subscript>Fe<Subscript>2</Subscript>As<Subscript>2</Subscript>

Superconductivity was achieved in Ti-doped iron-arsenide compound Sr₄Cr_0.8Ti_1.2O₆Fe₂As₂ (abbreviated as Cr-FeAs-42622). The X-ray diffraction measurement shows that this material has a layered structure with the space group of P4/nmm, and with the lattice constants a = b = 3.9003 Å and c = 15.8376 Å. Clear diamagnetic signals in ac susceptibility data and zero-resistance in resistivity data were detected at about 6 K, confirming the occurrence of bulk superconductivity. Meanwhile we observed a superconducting transition in the resistive data with the onset transition temperature at 29.2 K, which may be induced by the nonuniform distribution of the Cr/Ti content in the FeAs-42622 phase.     

Investigation of the dielectric,optical and photorefractive properties of Sb-doped Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> crystals

In this work we report results on electro-physical, optical and photorefractive investigations for Sb-doped Sn₂P₂S₆ crystals. The crystals are obtained by two methods: the vapour-transport technique and the Bridgman technique using stoichiometric Sn₂P₂S₆ composition with different amounts of antimony in the initial compound. The good optical quality of the crystals obtained with the Bridgman technique is underlined. The dependences of the photorefractive two-beam coupling coefficient and the grating build-up time are investigated at the wavelength of 633 nm. It is found that the sample doped with 1.5% of Sb is characterized by an optimal combination of the main photorefractive parameters exhibiting a fairly high two-beam coupling coefficient (up to 20 cm⁻¹) and a short response time (1.3 ms) that is the shortest among all the previously studied Sn₂P₂S₆ crystals in the red spectral region.     

Electrical and optical characterization of pulsed plasma of N<Subscript>2</Subscript>–H<Subscript>2</Subscript>

This paper considers the electrical and optical characterization of glow discharge pulsed plasma in N₂/H₂ gas mixtures at a pressures range between 0.5 and 4.0 Torr and discharge current between 0.2 and 0.6 A. Electron temperature and ion density measurements were performed employing a double Langmuir probe. They were found to increase rapidly as the H₂ percentage in the mixture was increased up to 20%. This increase slows down as the H₂ percentage in the gas mixture was increased above 20% at the same pressure. Emission spectroscopy was employed to observe emission from the pulsed plasma of a steady-state electric discharge. The discharge mainly emits within the range 280–500 nm. The emission consists of N₂ (C-X) 316, 336, 358 nm narrow peaks and a broad band with a maximum at λ_max = 427 nm. Also lines of N₂, N₂ ⁺ and NH excited states were observed. All lines and bands have their maximum intensity at the discharge current of 0.417 A. The intensities of the main bands and spectral lines are determined as functions of the total pressure and discharge current. Agreement with other theoretical and experimental groups was established.     

Heterophase states in 0.10PbTiO<Subscript>3</Subscript>-0.90Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> crystals

A new model of the elastic matching of phases is proposed, and heterophase structures near the morphotropic phase boundary in 0.10PbTiO₃-0.90Pb(Zn_1/3Nb_2/3)O₃ crystals are studied. Unique behavior of the unit cell parameters is found to favor the elastic matching of the ferroelectric tetragonal and orthorhombic phases under the conditions of complete or partial relaxation of internal mechanical stresses at a volume concentration ratio of these phases of about 20/80% and temperatures of T=20–300 K. Interrelations between the volume concentrations of different domain (twin) types and of the coexisting phases are analyzed.     

<Superscript>29</Superscript>Si MAS-NMR study of oxide conductors derived from the apatite-type La<Subscript>9.33</Subscript>Si<Subscript>6</Subscript>O<Subscript>26</Subscript> compound

The preparation of (La_9.33−2x/3Sr _x □_0.67−x/3)Si₆O₂₄O₂ (0 ≤ x ≤ 2) samples with different amounts of cation vacancies is reported. Structure and unit-cell parameters were deduced by Rietveld analysis of XRD patterns. Structural features that enhance oxygen conductivity in Sr-doped apatites are discussed. Up to three components were detected in ²⁹Si MAS-NMR spectra which change with the amount and distribution of cation vacancies. In general, oxygen conductivity increases with the amount of vacancies at La1 (6h) sites, passing through a maximum for x = 0.4. In the case of activation energy, a minimum is detected near x = 1.2, indicating that entropic and enthalpic change in different ways. The presence of cation vacancies should enhance oxygen hopping along c-axis; however, the analysis of the frequency dependence of conductivity suggests that oxygen motions are produced along three axes.