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.     

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.     

Study of mechanochemically prepared nanocrystalline La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript>

The nanocrystalline La_0.8Sr_0.2MnO₃ (LSM) is prepared by varying the revolutions per minute and milling time of planetary monomill during the mechanochemical method. The LSM forms in a relatively shorter milling time with an increase in the milling speed from 250 to 600 rpm. The structural phase transition from orthorhombic to rhombohedral phase in the LSM prepared by ball milling at the speed 250 rpm for 36 h is seen due to sintering it at 700 °C for 4 h. The crystallite size reduces with the increase in both the milling speed and the milling time individually or combined. The microhardness (HV) and sintered density increase with the reduction in the crystallite size. The temperature-activated transition temperature is suppressed by reducing the grain size in the nanometer range. The electrical dc conductivity increases with the reduction in the grain/crystallite size.     

Genesis,structural, and transport properties of La<Subscript>2</Subscript>Mo<Subscript>2-x</Subscript>W<Subscript>x</Subscript>O<Subscript>9</Subscript> prepared via mechanochemical activation

Fast oxide-ion conductors La₂Mo_2-xW_xO₉ (x = 0–1) have been prepared using mechanochemical activation (MA) of starting oxides in a high-power planetary ball mill. Studies of La₂Mo_2-xW_xO₉ genesis and structural properties using thermal analysis, XRD, SEM, IR, and Raman spectroscopy have revealed that MA results in the formation of an amorphous precursor, while the cubic β-phase is formed after calcination at 700–900 °C. Due to a high dispersion of powders, high-density pellets of W-LAMOX ceramics have been obtained already after sintering at 950 °C. Their electrical conductivity measured by the impedance spectroscopy depends on the W concentration being sufficiently high (up to 5.6?10^?3 S/cm at 630 °C) at temperatures below 650 °C.     

Enhanced electrochemical performance of Cu<Subscript>2</Subscript>O-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode material for lithium-ion batteries

Li₄Ti₅O₁₂/Cu₂O composite was prepared by ball milling Li₄Ti₅O₁₂ and Cu₂O with further heat treatment. The structure and electrochemical performance of the composite were investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Li₄Ti₅O₁₂/Cu₂O composite exhibited much better rate capability and capacity performance than pristine Li₄Ti₅O₁₂. The discharge capacity of the composite at 2 C rate reached up to 122.4 mAh g^?1 after 300 cycles with capacity retention of 91.3 %, which was significantly higher than that of the pristine Li₄Ti₅O₁₂ (89.6 mAh g^?1). The improvement can be ascribed to the Cu₂O modification. In addition, Cu₂O modification plays an important role in reducing the total resistance of the cell, which has been demonstrated by the electrochemical impedance spectroscopy analysis.     

Fabrication and laser performance of highly transparent Nd:YAG ceramics from well-dispersed Nd:Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowders by freeze-drying

Well-dispersed Nd:Y₂O₃ powders with uniform particle size of about 60 nm were synthesized from freeze-dried precursors. Highly transparent 2 at.% Nd:YAG ceramics were fabricated from the as-synthesized Nd:Y₂O₃ powders and commercial Al₂O₃ powders by vacuum sintering at 1,750 °C for 5 h. Phase evolution, microstructures, and spectroscopic properties of the Nd:YAG transparent ceramics were investigated. Freeze-drying played an important role in the synthesis of high-quality Nd:Y₂O₃ nanosized powders, which were essential for the fabrication of highly transparent Nd:YAG ceramics. Optical transmittance of a 3-mm thick sample reached 82% in the wavelength range of 200–900 nm. 5.23 W output power was obtained with 14.3 W diode laser pumping, giving a slope efficiency of 36.5%.     

Effect of sintering conditions on the properties of sol-gel-derived Li<Subscript>1.3</Subscript>Al<Subscript>0.3</Subscript>Ti<Subscript>1.7</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ was prepared by sol-gel method under different sintering conditions. The structural identification, surface morphology, electrochemical window, ionic conductivity, and activation energy of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets were investigated by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. It is found that the sintering temperature and time have considerable effect on the properties of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets. The Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellet sintered at 900 °C for 2 h is denser than the pellets sintered at other conditions. Different sintering conditions result in the sintered pellet with different porosity. However, the sintering conditions have little effect on the electrochemical window of Li_1.3Al_0.3Ti_1.7(PO₄)₃. Among the Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered at various conditions, the pellet sintered at 900 °C for 2 h shows the highest ionic conductivity of 3.46 × 10⁻⁴ S cm⁻¹ and the lowest activation energy of 0.2821 eV.     

Nanocrystalline CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> powders prepared by egg white solution route: synthesis,characterization and its giant dielectric properties

Nanocrystalline CaCu₃Ti₄O₁₂ powders with particle sizes of 50–90 nm were synthesized by a simple method using Ca(NO₃)₂·4H₂O, Cu(NO₃)₂·4H₂O, titanium(diisoproproxide) bis(2,4-pentanedionate) and freshly extracted egg white (ovalbumin) in aqueous medium. The synthesized precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at above 400 °C. The precursor was calcined at 700 and 800 °C in air for 8 h to obtain nanocrystalline powders of CaCu₃Ti₄O₁₂. The calcined CaCu₃Ti₄O₁₂ powders were characterized by XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 °C for 16 h. The XRD results indicated that all sintered samples have a typical perovskite CaCu₃Ti₄O₁₂ structure and a small amount of CuO, although the sintered sample of the 700 °C calcined powders contained some amount of CaTiO₃. SEM micrographs showed the average grain sizes of 12.0±7.8 and 15.5±8.9 μm for the sintered CaCu₃Ti₄O₁₂ ceramics prepared using the CaCu₃Ti₄O₁₂ powders calcined at 700 and 800 °C, respectively. The sintered samples exhibit a giant dielectric constant, ε^′ of ∼ 1.5–5×10⁴. The dielectric behavior of both samples exhibits Debye-like relaxation, and can be explained based on a Maxwell–Wagner model. PACS 77.22.Gm; 81.05.Je; 81.07.Wx; 81.20.Ev     

Magnetic properties of the Gd<Subscript>2</Subscript>V<Subscript>0.67</Subscript>Mo<Subscript>1.33</Subscript>O<Subscript>7</Subscript> and Y<Subscript>2</Subscript>VMoO<Subscript>7</Subscript> pyrochlore compounds

It is demonstrated that 50% substitution of vanadium for molybdenum in the pyrochlore lattice of the complex oxide Y₂(V _x Mo_{1 ? x} )₂O₇ results in a transition from the spin-glass ground state (at x = 0) to the ferromagnetic state in Y₂VMoO₇ (a = 10.1645(2) Å, T _C = 55 K). The Gd₂V_0.67Mo_1.33O₇ compound (a = 10.2862(3) Å) is a ferromagnet with T _C (84 K) exceeding that of undoped Gd₂MnO₂O₇.     

Influence of carbon additive on the properties of spherical Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> and LiFePO<Subscript>4</Subscript> materials for lithium-ion batteries

Preparing spherical particles with carbon additive is considered as one effective way to improve both high rate performance and tap density of Li₄Ti₅O₁₂ and LiFePO₄ materials. Spherical Li₄Ti₅O₁₂/C and LiFePO₄/C composites are prepared by spray-drying–solid-state reaction method and controlled crystallization–carbothermal reduction method, respectively. The X-ray diffraction characterization, scanning electron microscope, Brunauer–Emmett–Teller, alternating current impedance analyzing, tap density testing, and electrochemical property measurements are investigated. After hybridizing carbon with a proper quantity, the crystal grain size of active materials is remarkably decreased and the electrochemical properties are obviously improved. The Li₄Ti₅O₁₂/C and LiFePO₄/C composites prepared in this work are spherical. The tap density and the specific surface area are as high as 1.71 g cm⁻³ and 8.26 m² g⁻¹ for spherical Li₄Ti₅O₁₂/C, which are 1.35 g cm⁻³ and 18.86 m² g⁻¹ for spherical LiFePO₄/C powders. Between 1.0 and 3.0 V versus Li, the reversible specific capacity of the Li₄Ti₅O₁₂/C is more than 150 mAh g⁻¹ at 1.0-C rate. Between 2.5 and 4.2 V versus Li, the reversible capacity of the LiFePO₄/C is close to 140 mAh g⁻¹ at 1.0-C rate.     

Structural evolutions of the mechanically alloyed Al<Subscript>70</Subscript>Cu<Subscript>20</Subscript>Fe<Subscript>10</Subscript> powders

Elemental mixtures of Al, Cu, Fe powders with the nominal composition of Al₇₀Cu₂₀Fe₁₀ were mechanically alloyed in a planetary ball mill for 80 h. Subsequent annealing of the as-milled powders were performed at 600–800°C temperature range for 4 h. Structural characteristics of the mechanically alloyed Al₇₀Cu₂₀Fe₁₀ powders with the milling time and the heat treatment were investigated by X-ray diffraction (XRD), differential scanning calorimeter (DSC) and differential thermal analysis (DTA). Mechanical alloying of the Al₇₀Cu₂₀Fe₁₀ did not result in the formation of icosahedral quasicrystalline phase (i-phase) and a long time milling resulted in the formation of β-Al(Cu,Fe) solid solution phase (β-phase). The i-phase was observed only for short-time milled powders after heat treatment above 600°C. The β-phase was one of the major phases in the Al₇₀Cu₂₀Fe₁₀ alloy. The w-Al₇Cu₂Fe₁ phase (w-phase) was obtained only after heat treatment of the short-time milled and unmilled samples. The present investigation indicated that a suitable technique to obtain a large amount of quasicrystalline powders is to use a combination of short-time milling and subsequent annealing.     

Photolumiscent Properties of Nanorods and Nanoplates Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

Nanorods and nanoplates of Y₂O₃:Eu³⁺ powders were synthesized through the thermal decomposition of the Y(OH)₃ precursors using a microwave-hydrothermal method in a very short reaction time. These powders were analyzed by X-ray diffraction, field emission scanning electron microscopy, Fourrier transform Raman, as well as photoluminescence measurements. Based on these results, these materials presented nanoplates and nanorods morphologies. The broad emission band between 300 and 440 nm ascribed to the photoluminescence of Y₂O₃ matrix shifts as the procedure used in the microwave-hydrothermal assisted method changes in the Y₂O₃:Eu³⁺ samples. The presence of Eu³⁺ and the hydrothermal treatment time are responsible for the band shifts in Y₂O₃:Eu³⁺ powders, since in the pure Y₂O₃ matrix this behavior was not observed. Y₂O₃:Eu³⁺ powders also show the characteristic Eu³⁺ emission lines at 580, 591, 610, 651 and 695 nm, when excited at 393 nm. The most intense band at 610 nm is responsible for the Eu³⁺ red emission in these materials, and the Eu³⁺ lifetime for this transition presented a slight increase as the time used in the microwave-hydrothermal assisted method increases.     

Structural and catalytic properties of ZnO and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanostructures loaded with metal nanoparticles

Nanostructured zinc oxide (ZnO) nanobelts and aluminum oxide (Al₂O₃) nanoribbons have been grown successfully from the vapor phase. XRD results confirmed the purity and the high quality of the formed crystalline materials. TEM images showed that ZnO nanostructures grew in the commonly known tetrapod structure with nanobelts separated from the tetrapods with an average width range of 10–30 nm and a length of about 500 nm. Al₂O₃ nanostructures grew in the form of nanoribbons with an average width range of 20–30 nm and a length of up to 1 μm. The catalytic oxidation of CO gas into CO₂ gas over the synthesized nanostructures is also reported. Higher catalytic activity was observed for Pd nanoparticles loaded on the ZnO nanobelts (100% conversion at 270 °C) and Al₂O₃ nanoribbons (100% conversion at 250 °C). The catalytic activity increased in the order Cu < Co < Au < Pd for the metal-loaded nanostructures. The preparation methods could be applied for the synthesis of novel nanostructures of various materials with novel properties resulting from the different shapes and morphologies.     

Ferroelectric and dielectric properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> thin films grown on Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> film layer

Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi₄Ti₄O₁₅ grown on Bi₄Ti₃O₁₂, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared on a Pt(111)/Ti/SiO₂/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P _r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm² at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 10¹⁰ switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi₄Ti₄O₁₅ on Bi₄Ti₃O₁₂ ferroelectric thin films were better than those of the SrBi₄Ti₄O₁₅ grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth kinetics of SrBi₄Ti₄O₁₅ on the c-axis-oriented Bi₄Ti₃O₁₂ layer or on the Pt-coated Si substrate.     

Electrophysical properties and the structure of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> compound thermally restored after low-temperature decomposition

The electrophysical properties and structure of the nonstoichiometric high-temperature superconductor YBa₂Cu₃O _y restored at T = 930–950°C after low-temperature decomposition (T = 200°C) into phases different in the oxygen content have been studied. It has been shown that, unlike heat treatments at T ≤ 900°C, the superconducting properties are almost completely restored for 3–5 h during grain recrystallization, which is impossible at lower temperatures. After short-term annealing at T = 930–950°C (for 1–2 h), the ceramic material still contains a significant number of structural defects, most likely, in cation sublattices. These defects can contribute to the pinning of magnetic vortices, which substantially increases the critical current density in magnetic fields up to 2 T as compared to ceramic materials produced by the conventional technology.     

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.     

Preparation and electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Ti<Subscript>4</Subscript>O<Subscript>7</Subscript> composite for lithium-ion batteries

In order to improve the rate capability of Li₄Ti₅O₁₂, Ti₄O₇ powder was successfully fabricated by improved hydrogen reduction method, then a dual-phase composite Li₄Ti₅O₁₂/Ti₄O₇ has been synthesized as anode material for lithium-ion batteries. It is found that the Li₄Ti₅O₁₂/Ti₄O₇ composite shows higher reversible capacity and better rate capability compared to Li₄Ti₅O₁₂. According to the charge-discharge tests, the Li₄Ti₅O₁₂/Ti₄O₇ composite exhibits excellent rate capability of 172.3 mAh g^?1 at 0.2 C, which is close to the theoretical value of the spinel Li₄Ti₅O₁₂. More impressively, the reversible capacity of Li₄Ti₅O₁₂/Ti₄O₇ composite is 103.1 mAh g^?1 at the current density of 20 C after 100th cycles, and it maintains 84.8% of the initial discharge capacity, whereas that of the bare spinel Li₄Ti₅O₁₂ is only 22.3 mAh g^?1 with a capacity retention of 31.1%. The results indicate that Li₄Ti₅O₁₂/Ti₄O₇ composite could be a promising anode material with relative high capacity and good rate capability for lithium-ion batteries.     

Growth and sintering effects of hydrated polycrystalline Li<Subscript>2</Subscript>WO<Subscript>4</Subscript>

Polycrystalline Li₂WO₄ was sintered at temperatures, 400, 450, 500, 550, 600, 650, and 700 °C. After sintering at each particular temperature, the Li₂WO₄ was cooled to room temperature. The X-ray diffraction pattern of Li₂WO₄ exhibits dominant peaks attributable to 7Li₂WO₄.4H₂O (cubic) and Li₂WO₄ (hexagonal) and thus reveals the extent of hydration of the material. The composition varies on heating at several temperatures as shown by the presence of new peaks in the diffractogram. Thermogravimetric analysis is used to correlate respective structural and thermal properties in variation. The impedance spectra show the presence of a semicircle in the higher frequency regions and straight line behaviors at lower frequencies. SEM micrographs depict the image of sintered Li₂WO₄. Grain growth studies reveal the sensitiveness of grain toward temperature. The maximum grain size is observed to be ≈5.7 μm at 700 °C.     

First-principle calculations for electronic structure and bonding properties in layered Na<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript>

First-principles calculations of Na₂Ti₃O₇ have been carried out with density-functional theory (DFT) and ultrasoft pseudopotentials. The electronic structure and bonding properties in layered Na₂Ti₃O₇ have been studied through calculating band structure, density of states, electron density, electron density difference and Mulliken bond populations. The calculated results reveal that Na₂Ti₃O₇ is a semiconductor with an indirect gap and exhibits both ionic and covalent characters. The stability of the (Ti₃O₇)²⁻ layers is attributed to the covalent bonding of strong interactions between O 2p and Ti 3d orbitals. Furthermore, the O atoms located in the innerlayers interact more strongly with the neighboring Ti atoms than those in the interlayer regions. The ion-exchange property is due to the ionic bonding between the Na⁺ and (Ti₃O₇)²⁻ layers, which can stabilize the interlayers of layered Na₂Ti₃O₇ structure.     

Integrated investigation of the Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> phase stability

The Li₄Ti₅O₁₂ is applied in lithium ion batteries as anode material, which can be synthesized by various synthesis techniques. In this study, the molten salt synthesis technique at low temperatures, i.e. 350 °C, was applied to synthesize Li₄Ti₅O₁₂. Surprisingly, the Li₄Ti₅O₁₂ was not formed according to XRD analysis, which raised question about the stability range of Li₄Ti₅O₁₂. To investigate the stability of Li₄Ti₅O₁₂ at low temperatures, the high-temperature calcined Li₄Ti₅O₁₂ powder was equilibrated in the LiCl-KCl eutectic salt at 350 °C. The result of experiment revealed that the Li₄Ti₅O₁₂ is not decomposed. Results of ab initio calculations also indicated that the Li₄Ti₅O₁₂ phase is a stable phase at 0 K. The products of molten salt synthesis technique were then annealed at 900 °C, which resulted in the Li₄Ti₅O₁₂ formation. It was concluded that the Li₄Ti₅O₁₂ is a stable phase at low temperatures and the reasons for not forming the Li₄Ti₅O₁₂ by molten salt technique at low temperature are possibly related to activation energy and kinetic barriers. The Li₄Ti₅O₁₂ formation energy is also very small, due to the results of ab initio calculations.