Spherical shape BaO-ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass powders prepared by spray pyrolysis

Fine-sized BaO-ZnO-B₂O₃-SiO₂ (BZBS) glass powders were directly prepared by high temperature spray pyrolysis. The hollow glass powders prepared at low preparation temperature of 1000 °C had a low density of 2.65 g/cm³. However, the densities of the BZBS powders obtained at preparation temperatures of 1200 and 1400 °C were each 3.92 and 4.13 g/cm³. The mean size of the BZBS glass powders prepared by spray pyrolysis at preparation temperature of 1400 °C was 0.98 μm. The glass transition temperature (T_g) of the prepared BZBS glass powders was 518.9 °C. The dielectric layers formed from the prepared BZBS glass powders with a dense structure had a clean surface and a dense inner structure without voids at the firing temperature of 580 °C. The transparencies of the dielectric layers formed from the prepared BZBS glass powders were higher than 90% within the visible range. PACS 42.70.Ce; 85.60.Pg; 71.55.Jv     

Fabrication and electrochemical performance of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> impregnated porous YSZ cathode

La_0.5Sr_0.5CoO₃-yttria-stabilized zirconia (LSCO-YSZ) composite cathode for solid oxide fuel cell (SOFC) has been fabricated by wet impregnation method. Nitrate precursors of La, Sr, and Co have been impregnated into the pre-sintered porous YSZ matrix, which is converted into LSCO phase after calcination at 850 °C in the presence of glycine as confirmed from X-ray diffraction. LSCO of 5, 7, and 10 wt% impregnated porous YSZ have been electrochemically characterized using 2-probe AC conductivity method. Maximum ionic conductivity of 0.27 S/cm at 800 °C and activation energy of 0.15 eV between 600 and 800 °C have been observed for 10 wt% LSCO-YSZ cathode. Area-specific resistance of 1.01 Ω cm² at 800 °C is estimated for the electrolyte-supported half-cell (10 wt% LSCO-YSZ/YSZ). After testing the LSCO-YSZ cathode matrix, the electrolyte-supported full cell (10 wt% LSCO-YSZ/YSZ/NiO-YSZ) has been tested and produced maximum power density 51.12 mW/cm² (109.38 mA/cm²) at 800 °C. The electrolyte-supported full cell exhibited 6 Ω cm² electrode polarization at 800 °C in H₂, which is in higher side leading to low performance. LSCO-YSZ/YSZ/NiO-YSZ SOFC found to give stable performance up to 2 h and scanning electron microscopy analysis has been carried out before and after cell testing to assess the morphological changes.     

Enhanced dielectric properties of polyvinylidene fluoride with addition of SnO2 nanoparticles

In this letter, SnO₂/polyvinylidene fluoride (PVDF) nanocomposites with outstanding dielectric properties were fabricated. The SEM and TEM images showed that SnO₂ nanoparticles with size of 5–7 nm dispersed homogeneously in polymer matrix. The significantly improved dielectric constant was well explained by percolation theory. The nanocompo‐ sites can retain a certain value of breakdown field. The maximum energy density of SnO₂/PVDF nanocomposites was 5.4 J/cm³, two times that of the pure polyvinylidene fluoride. These findings suggest that SnO₂/PVDF nanocomposites are suitable candidates for energy storage applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

CeO<Subscript>2</Subscript> and Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> modified Ni-YSZ anode for solid oxide fuel cell

Ni sintering at high temperature (～ 800 °C) operation drastically degrades the performance of Ni-yttria-stabilized zirconia (YSZ) anode in solid oxide fuel cell (SOFC). Mixed ionic and electronic conductive oxides such as CeO₂ and Nb₂O₅ enhance the dispersion of Ni, CeO₂ enhances the redox behavior and promotes charge transfer reactions, and Nb₂O₅ increases the triple phase boundary. In the present work, anode-supported SOFC is fabricated and tested in H₂ fuel at 800 °C. YSZ and lanthanum strontium manganite (LSM)-YSZ are used as the electrolyte and composite cathode with NiO-YSZ, CeO₂-NiO-YSZ, and Nb₂O₅-NiO-YSZ as an anode. The peak power density obtained for the cell with 10% CeO₂–30% NiO-YSZ anode at the 5 and 25 h of operation is 330 and 290 mW cm^?2 which is higher than that for 40% NiO-YSZ anode (275 mW cm^?2 at 5 h). The peak power density obtained for the cell with 10% Nb₂O₅–30% NiO-YSZ anode at the 5 and 25 h of operation is 301 and 285 mW cm^?2 which is higher than that for 40% NiO-YSZ anode (275 mW cm^?2 at 5 h). Physical characterization has been carried to study morphology, elemental analysis, particle size, and phase formation of the fabricated anode before and after cell operation to correlate the cell performance.     

Low-temperature sintering effects on NASICON-structured LiSn<Subscript>2</Subscript>P<Subscript>3</Subscript>O<Subscript>12</Subscript> solid electrolytes prepared via citric acid-assisted sol-gel method

LiSn₂P₃O₁₂ with sodium (Na) super ionic conductor (NASICON)-type rhombohedral structure was successfully obtained at low sintering temperature, 600 °C via citric acid-assisted sol-gel method. However, when the sintering temperature increased to 650 °C, triclinic structure coexisted with the rhombohedral structure as confirmed by X-ray diffraction analysis. Conductivity–temperature dependence of all samples were studied using impedance spectroscopy in the temperature range 30 to 500 °C, and bulk, grain boundary and total conductivity increased as the temperature increased. The highest bulk conductivity found was 3.64?×?10^?5 S/cm at 500 °C for LiSn₂P₃O₁₂ sample sintered at 650 °C, and the lowest bulk activation energy at low temperature was 0.008 eV, showing that sintering temperature affect the conductivity value. The voltage stability window for LiSn₂P₃O₁₂ sample sintered at 600 °C at ambient temperature was up to 4.4 V. These results indicated the suitability of the LiSn₂P₃O₁₂ to be exploiting further for potential applications as solid electrolytes in electrochemical devices.     

Novel Ag–BaTiO3/PVDF three-component nanocomposites with high energy density and the influence of nano-Ag on the dielectric properties

Novel Ag–BaTiO₃/PVDF (polyvinylidene fluoride) three-component nanocomposites and traditional BaTiO₃/PVDF two-component nanocomposites were prepared by the same procedures. The dielectric properties of these two kinds of composites were compared. The results showed that the kind of three-component nanocomposites had better dielectric properties. The energy density of such kind of composites could reach nearly 10 J/cm³, which indicated that these nanocomposites could be used as the dielectric layers of pulse-power capacitors. The Coulomb blockade effect was used to explain the dielectric breakdown properties and the resistivities under high electric field of such new kind of nanocomposites.     

The effect of LiCF<Subscript>3</Subscript>SO<Subscript>3</Subscript> on the complexation with potato starch-chitosan blend polymer electrolytes

This work examines the effect of lithium trifluoromethanesulfonate (LiCF₃SO₃) and glycerol on the conductivity and dielectric properties of potato starch-chitosan blend-based electrolytes. The electrolytes are prepared via solution cast technique. From X-ray diffraction (XRD) analysis, the blend of 50 wt.% starch and 50 wt.% chitosan is found to be the most amorphous blend. Fourier transform infrared (FTIR) spectroscopy studies show the interaction between the electrolyte materials. The room temperature conductivity of pure starch-chitosan film is found to be (2.85 ± 1.31) × 10^?10 S cm^?1. The incorporation of 45 wt.% LiCF₃SO₃ increases the conductivity to (7.65 ± 2.27) × 10^?5 S cm^?1. Further conductivity enhancement up to (1.32 ± 0.35) × 10^?3 S cm^?1 has been observed on addition of 30 wt.% glycerol. This trend in conductivity is verified by XRD and dielectric analysis. The temperature dependence of conductivity of all electrolytes are Arrhenian.     

Temperature evolution of the dielectric response function of Pb(Fe<Subscript>0.95</Subscript>Sc<Subscript>0.05</Subscript>)<Subscript>2/3</Subscript>W<Subscript>1/3</Subscript>O<Subscript>3</Subscript> relaxor ceramics in a wide frequency range

Electrodynamic properties of Pb(Fe_0.95Sc_0.05)_2/3W_1/3O₃ solid solution belonging to A(B'B'')O₃ perovskite structural family have been investigated by broadband dielectric spectroscopy in a wave-number range of (4 × 10^–9–4 × 10³) cm^–1 and a temperature range of 100–600 K. The influence of low-frequency relaxations on the vibrational spectrum is determined within the four-parameter factorized dispersion model. Anomalies in the behavior of the dielectric response function are found near the temperature-diffuse maximum of permittivity.     

Influence of heat treatment process in In<Subscript>2</Subscript>O<Subscript>3</Subscript>-MWCNTs as photoanode in DSSCs

Indium oxide-multi-walled carbon nanotubes (In₂O₃-MWCNTs) were prepared by sol-gel method for DSSCs. The synthesis of indium oxide (In₂O₃) was carried out by dissolving indium chloride (InCl₃) in a solvent of 2-methoxyethanol. Different annealing temperatures of 400, 450, 500, 550, and 600 °C were proposed in this study. The changes in the structural properties were analyzed by means of X-ray diffraction (XRD) and atomic force microscopy (AFM) analysis. The XRD spectrum estimated the average crystallite sizes of 3 nm for each sample. AFM results indicated very rough surface area of the films where it increased linearly from 1.8 to 11 nm as the annealing temperature increases. The In₂O₃-MWCNTs-based DSSC exhibited good photovoltaic performance with power conversion efficiency (η), photocurrent density (J _sc ), open circuit voltage (V _oc ), and fill factor (FF) of 1.13 %, 5.5 mA/cm², 0.53 V, and 0.42, respectively. Even though the film annealed at 450 °C exhibited low τ _eff, it achieved the greatest D _eff of 29.67 cm² s^?1 which provides an efficient pathway for the photogenerated electrons with minimum electron recombination loss that increased the J _sc and V _oc in the DSSC. The obtained structural and electron transport analysis was proposed as a suitable benchmark for In₂O₃-MWCNTs-based dye-sensitized solar cell (DSSCs) application. Hence, this study suggests that the optimum temperature for In₂O₃-MWCNTs is at annealing temperature of 450 °C prepared via sol-gel method.     

Synthesis and electrochemical performance of spherical LiNi<Subscript>0.8</Subscript>Co<Subscript>0.15</Subscript>Ti<Subscript>0.05</Subscript>O<Subscript>2</Subscript> cathode materials with high tap density

A series of spherical LiNi_0.8Co_0.15Ti_0.05O₂ cathode materials were synthesized through co-oxidation-controlled crystallization method followed by solid-state reaction at different calcination temperatures under oxygen flowing. The crystal structure and particles morphology of the as-prepared powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. All samples correspond to the layered α-NaFeO₂ structure with R-3m space group. The LiNi_0.8Co_0.15Ti_0.05O₂ prepared at 800 °C presents a better hexagonal ordering structure and better spherical particles and possesses a high tap density of 3.22 g cm^?3. Meanwhile, the NCT-2 sample exhibits an advanced electrochemical performance with an initial discharge capacity of 174.2 mAh g^?1 and capacity retention of 86.7 % after 30 cycles at 0.2 C.     

Magnetoelectric Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> and relativity theory

Based on the dielectric continuum phonon model, uniaxialmodel and force balance equation the mobility of two dimensional electrongas in wurtzite Al_xGa_1-xN/GaN/Al_xGa_1-xN quantum wells isdiscussed theoretically within the temperature range dominated by opticalphonons. The dependences of the electron mobility on temperature, Al molarfraction and electron sheet density are presented including hydrostaticpressure effect. The built-in electric field is also taken into account. Itis found that under normal pressure the main contribution to the mobility isfrom the scattering of interface optical phonons in narrow (for well widthd < 12 Å) and wide (for d > 117 Å and d > 65 Å for finitelythick barriers and infinitely thick ones, respectively) wells, whereas thatis from the scattering of confined optical phonons in a well with anintermediate width. It is shown that the electron mobility decreases withincreasing Al molar fraction and temperature, whereas increases obviouslywith increasing electron sheet density. The theoretical calculated electronmobility is 978 cm²/V?s which is higher than an available experimentaldata 875 cm²/V?s when x equals to 0.58 at room temperature. Theresults under hydrostatic pressure considering the modification of strainindicate that the mobility increases slightly as hydrostatic pressureincreases from 0 to 10 GPa.     

Novel nanocomposite membranes based on polybenzimidazole and Fe<Subscript>2</Subscript>TiO<Subscript>5</Subscript> nanoparticles for proton exchange membrane fuel cells

In this work, Fe₂TiO₅ nanoparticles were used for improving the proton conductivity, and water and acid uptake of polybenzimidazole (PBI)-based proton exchange membranes. The nanocomposite membranes have been prepared using different amounts of Fe₂TiO₅ nanoparticles and dispersed into a PBI membrane with the solution-casting method. The prepared membranes were then physico-chemically and electrochemically characterized for use as electrolytes in high-temperature PEMFCs. The PBI/Fe₂TiO₅ membranes (PFT) showed a higher acid uptake and proton conductivity compared with the pure PBI membranes. The highest acid uptake (156 %) and proton conductivity (78 mS/cm at 180 °C) were observed for the PBI nanocomposite membranes containing 4 wt% of Fe₂TiO₅ nanoparticles (PFT₄). The PFT₄ composite membrane showed 380 mW/cm² power density and 760 mA/cm² current density in 0.5 V at 180 °C at dry condition. The above results indicated that the PFT₄ nanocomposite membranes could be utilized as proton exchange membranes for high-temperature fuel cells.     

Characterization and electrical properties of high-<Emphasis Type="Italic">k</Emphasis> GdScO<Subscript>3</Subscript> thin films grown by atomic layer deposition

Gadolinium scandium oxide (Gd-scandate, GdScO₃) thin films were grown by atomic layer deposition (ALD) from β-diketonate precursors M(thd)₃ (M=Gd, Sc; thd=2,2,6,6-tetramethyl-3,5-heptanedionato) and ozone. The deposition parameters were optimized to produce films with the stoichiometric 1:1 metal ratio and a series of samples with nominal thicknesses of 5, 10, 15, and 20 nm were prepared. At 300 °C the metal precursor pulsing ratio Gd:Sc=5:6 yielded amorphous stoichiometric films and a growth rate of 0.21 Å/cycle. The films stayed amorphous up to 900 °C. The surface was probed with an AFM and the rms roughness was found to be 0.3 nm for the 5–20 nm thick films. The electrical properties of the as-deposited films proved to be very promising, with a dielectric constant of ～22 and leakage current density of 340 μA/cm², measured at -2 V.     

Synthesis and electrochemical properties of P2-Na<Subscript>2/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>2/3</Subscript>O<Subscript>2</Subscript>

The pure phase P2-Na_2/3Ni_1/3Mn_2/3O₂ was synthesized by a solid reaction process. The optimum calcination temperature was 850 °C. The as-prepared product delivered a capacity of 158 mAh g^?1 in the voltage range of 2–4.5 V, and there was a phase transition from P2 to O2 at about 4.2 V in the charge process. The P2 phase exhibited excellent intercalation behavior of Na ions. The reversible capacity is about 88.5 mAh g^?1 at 0.1 C in the voltage range of 2–4 V at room temperature. At an elevated temperature of 55 °C, it could remain as an excellent capacity retention at low current rates. The P2-Na_2/3Ni_1/3Mn_2/3O₂ is a potential cathode material for sodium-ion batteries.     

Investigation on lithium ion conductivity and structural stability of yttrium-substituted Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript>

Advanced Li-air battery architecture demands a high Li⁺ conductive solid electrolyte membrane that is electrochemically stable against metallic lithium and aqueous electrolyte. In this work, an investigation has been carried out on the microstructure, Li⁺ conduction behaviour and structural stability of Li₇La_3-x Y _x Zr₂O₁₂ (x = 0.125, 0.25 and 0.50) prepared by conventional solid-state reaction technique. The phase analysis of Li₇La_3-x Y _x Zr₂O₁₂ (x = 0.125, 0.25 and 0.50) sintered at 1200 °C by powder X-ray diffraction (PXRD) and Raman confirms the formation of high Li⁺ conductive cubic phase (\( Ia\overline{3}d \)) lithium garnets. Among the investigated lithium garnets, Li₇La_2.75Y_0.25Zr₂O₁₂ sintered at 1200 °C exhibits a maximized room temperature total (bulk + grain boundary) Li⁺ conductivity of 3.21 × 10^?4 S cm^?1 along with improved relative density of 96 %. The preliminary investigation on the structural stability of Li₇La_2.75Y_0.25Zr₂O₁₂ in the solutions of 1 M LiCl, dist. H₂O and 1 M LiOH at 30 °C/50 °C indicates that the Li₇La_2.75Y_0.25Zr₂O₁₂ is relatively stable against 1 M LiCl and dist. H₂O. Further electrochemical investigation is essential for practical application of Li₇La_2.75Y_0.25Zr₂O₁₂ as protective solid electrolyte membrane in aqueous Li-air battery.     

Hydrothermal synthesis of LiMnPO<Subscript>4</Subscript>-C(sp<Superscript>2</Superscript>) hybrids,conductive channels,and enhanced dielectric permittivity: a modulated ionic conductor

A nanohybrid C-LiMnPO₄ is important to tailor its electrochemical properties useful for Li⁺-ion batteries and photo-catalysis. In this article, we report a simple in situ C-LiMnPO₄ synthesis, wherein the LiMnPO₄ grows from a supersaturated solution LiOH·H₂O, MnSO₄·H₂O, and H₃PO₄ in water at 200 °C in an autoclave in a hydrothermal reaction and bonds in situ to nascent carbon of a surface layer on a surface reaction with a long chain hydrocarbon used during the reaction. A phase pure C-LiMnPO₄ is formed in a shape of nanorods (Pnma orthorhombic crystal structure), with 100–150 nm diameters, 150–800 nm lengths, and 2–3 nm thickness of a co-bonded C-sp² surface layer. The LiMnPO₄ rigidly co-bonds to C-sp² via O^2? in the PO₄ ^3? polygons in a joint surface layer that a single molecular bonding extends well up to 600 °C, with a due mass loss on an extended heating in air. The sample contains fine pores with an average 3.0 nm diameter and a 9.0 m²/g surface area. At room temperature, it develops a huge dielectric permittivity ε _r~1.9 × 10⁵ near 1 Hz frequencies, which on raising the frequency decays progressively to a fairly steady ε _r~1.5 × 10³ at ≥1 kHz. Bare LiMnPO₄ is a low dielectric phase, ε _r < 10. A non-Debye type of dielectric relaxation is shown in the modulus plots. As frequency approaches to 10⁵ Hz, nearly three orders of larger ac conductivity, 2.5 × 10^?5 Scm^?1 at 10⁶ Hz, develop over a carbon-free LiMnPO₄ value useful for the applications.     

Microstructural interpretation of conductivity and dielectric response of Ce<Subscript>0.9</Subscript>Eu<Subscript>0.1</Subscript>O<Subscript>1.95</Subscript> oxygen ion conductors

This work focuses on the structure property co-relation study of Eu³⁺-doped ceria nanomaterials prepared through citrate auto-ignition process and sintered at three different temperatures. The microstructure and dielectric properties were found to be affected by the sintering temperature. The particle size was found to play a major role to the migration of charge carriers in the samples. The dielectric constant has been found to control the formation of dopant-vacancy interaction though columbic interaction in defect pair (Eu′_Ce – V_o ^??)^? and neutral trimers (Eu′_Ce – V_o ^?? – Eu′_Ce). The sample sintered at 800 °C shows the lowest value of lattice parameter due to the highest value of dopant-vacancy interaction. The migration energy for oxygen vacancy conduction was found to increase with particle size that reduces the ionic conductivity values. The rate of hopping was found to decrease due to blocking of charge-carrier diffusion due to the growth of particle.     

The effect of NH<Subscript>4</Subscript>NO<Subscript>3</Subscript> towards the conductivity enhancement and electrical behavior in methyl cellulose-starch blend based ionic conductors

Solid polymer electrolytes based on methyl cellulose (MC)-potato starch (PS) blend doped with ammonium nitrate (NH₄NO₃) are prepared by solution cast technique. The interaction between the electrolyte’s materials is proven by Fourier transform infrared (FTIR) analysis. The thermal stability of the electrolytes is obtained from thermogravimetric analysis (TGA). The room temperature conductivity of undoped 60 wt.% MC-40 wt.% PS blend film is identified to be (1.04 ± 0.19) × 10^?11 S cm^?1. The addition of 30 wt.% NH₄NO₃ to the polymer blend has optimized the room temperature conductivity to (4.37 ± 0.16) × 10^?5 S cm^?1. Conductivity trend is verified by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dielectric analysis. Temperature-dependence of conductivity obeys Arrhenius rule. Conductivity is found to be influenced by the number density (n) and mobility (μ) of ions. From transference number measurements (TNM), ions are found to be the dominant charge carriers.     

Dielectric properties of Bi<Subscript>2</Subscript>PbNb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics prepared by different techniques

Different techniques for the synthesis of Bi₂PbNb₂O₉, namely the mixed oxide technique, molten salt synthesis, hydrothermal synthesis, co-precipitation and the tartaric acid gel method were investigated and the results on the dielectric properties are reported. The heat-treatment of the precursor powders was the same for all precursor powders. Sintering at 1040 °C under ambient pressure resulted in polycrystalline specimens, while hot-forging at 1040 °C with a pressure of 20 MPa produced c-axis aligned samples. Phase composition and crystallite orientation of the sintered bodies were analyzed by X-ray diffraction. Single-phase material was obtained in all cases. Hot-forging not only yielded c-axis orientation, but also increased the relative densities above 99.4%. The relative permittivity decreased for c-axis oriented material compared to polycrystalline ceramics. Values for the relative permittivity for the hot-forged specimens at 100 °C at 100 kHz varied between 165 and 250, depending on the fabrication method. The Curie temperature for the c-axis aligned samples was 568 °C, independent of the nature of the precursor powders. PACS 77.22.-d; 77.84.-s     

Elevated electrochemical property of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> originated from nano-sized Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>

By employment of nano-sized pre-prepared Mn₃O₄ as precursor, LiMn₂O₄ particles have been successfully prepared by facile solid state method and sol-gel route, respectively. And the reaction mechanism of the used precursors of Mn₃O₄ is studied. The structure, morphology, and element distribution of the as-synthesized LiMn₂O₄ samples are characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Compared with LiMn₂O₄ synthesized by facile solid state method (SS-LMO), LiMn₂O₄ synthesized by modified sol-gel route (SG-LMO) possesses higher crystallinity, smaller average particle size (~175 nm), higher lithium chemical diffusion coefficient (1.17 × 10^?11 cm² s^?1), as well as superior electrochemical performance. For example, the cell based on SG-LMO can deliver a capacity of 85.5 mAh g^?1 at a high rate of 5 °C, and manifests 88.3% capacity retention after 100 cycles at 0.5 °C when cycling at 45 °C. The good electrochemical performance of the cell based on SG-LMO is ascribed mainly to its small particle size, high degree of dispersion, and uniform element distribution in bulk material. In addition, the lower polarization potential accelerates Li⁺ ion migration, and the lower atom location confused degree maintains integrity of crystal structure, both of which can effectively improve the rate capability and cyclability of SG-LMO.