Li(4−x)/3Ti(5−2x)/3CrxO4 (0 ≤ x ≤ 0.9) spinels: New negatives for lithium batteries

Members of the spinel solid solution between Li_4/3Ti_5/3O₄ and LiCrTiO₄, i.e., Li_(4−x)/3Ti_(5−2x)/3Cr_xO₄ (0 ≤ x ≤ 0.9), have been investigated as possible negative electrodes for future lithium-ion batteries. Electrochemical behaviour have been studied over the potential range 1–3.5 V vs Li⁺/Li. Results are promising with anodic capacities between 129 and 163 mA h/g with a flat operating voltage at about 1.5 V, which is attributed to the pair Ti⁴⁺/Ti³⁺. The inclusion of Cr³⁺ in the spinel structure enhances the specific capacity. In-situ X-ray diffraction experiments confirm that the reaction proceeds in a topotactic manner.     

Li2CuTi3O8–Li4Ti5O12 double spinel anode material with improved rate performance for Li-ion batteries

Ti-based anode materials with the nominal compositions Li₄Ti₅Cu_xO_12 + x (x = 0, 0.075, 0.15, 0.3, 0.6, 1.20 and 1.67) were synthesized at 800 °C by a solid-state reaction process. X-ray diffraction analysis indicated that the sintered samples were composed of intergrown spinel-type Li₄Ti₅O₁₂ and Li₂CuTi₃O₈, and a small amount of Li₂O. Scanning electron microscopy, electrical resistance measurement and galvanostatic cell cycling were also employed to characterize the structure and properties of the double spinel samples. It is proposed that the first lithiation of the component Li₂CuTi₃O₈ leads to the in situ production of Cu that can significantly improve the rate performance of Li₄Ti₅Cu_xO_12 + x. The optimal nominal composition is Li₄Ti₅Cu_0.15O_12.15.     

Calorimetric investigation of mixing enthalpy of liquid (Co + Cu + Zr) alloys at T = 1873 K

The enthalpies of mixing of liquid (Co + Cu + Zr) alloys have been determined using the high-temperature isoperibolic calorimeter. The measurements have been performed along three sections (x_Co/x_Cu = 3/1, 1/1, 1/3) with x_Zr = 0 to 0.55 at T = 1873 K. Over the investigated composition range, the partial mixing enthalpies of zirconium are negative. The limiting partial enthalpies of mixing of undercooled liquid zirconium in liquid (Co + Cu) alloys are (−138 ± 18) kJ · mol⁻¹ (the section x_Co/x_Cu = 3/1), (−155 ± 10) kJ · mol⁻¹ (the section x_Co/x_Cu = 1/1), and (−130 ± 22) kJ · mol⁻¹ (the section x_Co/x_Cu = 1/3). The integral mixing enthalpies are sign-changing. The isenthalpic curves have been plotted on the Gibbs triangle. The main features of the composition dependence of the integral mixing enthalpy of liquid ternary alloys are defined by the pair (Co + Zr) and (Cu + Zr) interactions.     

Study on the effect of Li doping in spinel Li4+xTi5−xO12 (0 ⩽ x ⩽ 0.2) materials for lithium-ion batteries

The effect of Li doping in spinel Li_4+xTi_5−xO₁₂ (0 ⩽ x ⩽ 0.2) materials on the structural and electrochemical properties were investigated. The ratio of the capacity in the voltage plateau (1.5 V) to the overall discharge capacity for Li_4.1Ti_4.9O₁₂ (x = 0.1) and Li_4.2Ti_4.8O₁₂ (x = 0.2) were higher than that of Li₄Ti₅O₁₂ especially at high current rates due to their enhanced lithium-ion and electronic conductivity by the substitution of Ti atoms by Li atoms. With the increasing of Li doping amount, lithium-ion and electronic conductivity of Li_4+xTi_5−xO₁₂ increased, however its cycling stability was depressed when the Li doping was of x = 0.2. The Li doping of x = 0.1, the appropriate Li doping amount, showed improved rate capability and better high rate performance comparing to undoped Li_4+xTi_5−xO₁₂ (x = 0).     

Synthesis and characterization of A-site deficient rare-earth doped BaZrxTi1−xO3 perovskite-type compounds

A-site deficient rare-earth doped BaZr_xTi_1?xO₃ (BZT) ceramics were prepared from a soft-chemistry route and by solid-state reaction (SSR). Perovskite-like single-phase diagrams for the BaTiO₃–La_2/3TiO₃–BaZrO₃ system were constructed for each method of synthesis. Infrared spectroscopy on (Ba_1?yLa_2y/3)Zr_xTi_1?xO₃ solid solution revealed a dramatic stress on the M–O (M = Ti, Zr) bonds due to the combined effect of A-site vacancies and the lower ionic radius of La³⁺ than that of Ba²⁺. A relationship between the M–O stretching vibration (υ) and the tolerance factor (t) was determined. (Ba_1?yLn_2y/3)Zr_0.09Ti_0.91O₃ (Ln = La, Pr, Nd) samples synthesized by SSR were selected for detailed studies. X-ray diffraction data were refined by the Rietveld method. Scanning electron microscopy on sintered compacts detected abnormal crystal growth and grain sizes in the range of about 1 μm up to 10 μm when the dopant concentration is 6.7 at. %. Impedance measurements exhibited that ferroelectric to paraelectric phase-transition temperature shifted to lower values as increasing rare-earth content. (Ba_1?yLn_2y/3)Zr_0.09Ti_0.91O₃ system showed a diffuse phase transition with a relaxor-like ferroelectric behaviour. Furthermore, the dielectric constant was enhanced with respect to non-doped BZT system.     

Microstructures and electrochemical hydrogen storage properties of novel Mg–Al–Ni amorphous composites

The amorphous Mg–Al–Ni composites were prepared by mechanical ball-milling of Mg₁₇Al₁₂ with x wt.% Ni (x = 0, 50, 100, 150, 200). The effects of Ni addition and ball-milling parameters on the electrochemical hydrogen storage properties and microstructures of the prepared composites have been investigated systematically. For the Mg₁₇Al₁₂ ball-milled without Ni powder, its particle size decreases but the crystal structure does not change even the ball-milling time extending to 120 h, and its discharge capacity is less than 15 mAh g^?1. The Ni addition is advantageous for the formation of Mg–Al–Ni amorphous structure and for the improvement of the electrochemical characteristics of the composites. With the Ni content x increasing, the composites exhibit higher degree of amorphorization. Moreover, the discharge capacity of the composite increases from 41.3 mAh g^?1 (x = 50) to 658.2 mAh g^?1 (x = 200) gradually, and the exchange current density I₀ increases from 67.1 mA g^?1 (x = 50) to 263.8 mA g^?1 (x = 200), which is consistent with the variation of high-rate dischargeability (HRD). The ball-milled Mg₁₇Al₁₂ + 200 wt.% Ni composite has the highest cycling discharge capacity in the first 50 cycles.     

Nb2O5 nanobelts: A lithium intercalation host with large capacity and high rate capability

In this study, Nb₂O₅ nanobelts, with a ca. ∼15 nm in thickness, ca. ∼60 nm in width and several tens of mircrometers in length, have first been used as the electrode material for lithium intercalation over the potential window of 3.0–1.2 V (vs. Li⁺/Li). It delivers an initial intercalation capacity of 250 mA hg⁻¹ at 0.1 Ag⁻¹ current density, corresponding to x = 2.5 for L_xNb₂O₅, and can still keep relative stable and reaches as large as 180 mA hg⁻¹ after 50 cycles. Surprisingly, the electrodes composed of Nb₂O₅ nanobelts can work smoothly even at high current density of 10 Ag⁻¹, and shows higher specific capacity and excellent cycling stable, as well as sloped feature in voltage profile. Cycling test indicates Nb₂O₅ nanobelts electrode shows a high reversible charge/discharge capacity, high rate capability with excellent cycling stability.     

Redox behavior and transport properties of La0.5−2xCexSr0.5+xFeO3−δ and La0.5−2ySr0.5+2yFe1−yNbyO3−δ perovskites

The effects of doping the mixed-conducting (La,Sr)FeO_3−δ system with Ce and Nb have been examined for the solid-solution series, La_0.5−2xCe_xSr_0.5+xFeO_3−δ (x = 0–0.20) and La_0.5−2ySr_0.5+2yFe_1−yNb_yO_3−δ (y = 0.05–0.10). Mössbauer spectroscopy at 4.1 and 297 K showed that Ce⁴⁺ and Nb⁵⁺ incorporation suppresses delocalization of p-type electronic charge carriers, whilst oxygen nonstoichiometry of the Ce-containing materials increases. Similar behavior was observed for La_0.3Sr_0.7Fe_0.90Nb_0.10O_3−δ at 923–1223 K by coulometric titration and thermogravimetry. High-temperature transport properties were studied with Faradaic efficiency (FE), oxygen-permeation, thermopower and total-conductivity measurements in the oxygen partial pressure range 10⁻⁵–0.5 atm. The hole conductivity is lower for the Ce- and Nb-containing perovskites, primarily as a result of the lower Fe⁴⁺ concentration. Both dopants decrease oxide-ion conductivity but the effect of Nb-doping on ionic transport is moderate and ion-transference numbers are higher with respect to the Nb-free parent phase, 2.2 × 10⁻³ for La_0.3Sr_0.7Fe_0.9Nb_0.1O_3−δ cf. 1.3 × 10⁻³ for La_0.5Sr_0.5FeO_3−δ at 1223 K and atmospheric oxygen pressure. The average thermal expansion coefficients calculated from dilatometric data decrease on doping, varying in the range (19.0–21.2) × 10⁻⁶ K⁻¹ at 780–1080 K.     

Impedance study on the correlation between phase transition and electrochemical degradation of Si-based materials

In order to explain the relationship between physical change and electrochemical degradation of Co–Co₃O₄ coated Si, impedance spectroscopy on Co–Co₃O₄ coated Si was conducted at various states during charge or discharge. Nyquist plots during Li⁺ insertion (charge) showed a unique behavior that below 70 mV vs. Li/Li⁺, the more Li⁺’s were inserted into the electrode, the larger its comprehensive resistance was getting. During Li⁺ extraction (discharge), electrode resistance was decreased after going through 0.43 V vs Li/Li⁺. When these data were fitted with the ordinary equivalent circuit which is composed of electrolyte resistance, charge transfer resistance and contact resistance, there was an abrupt augmentation of charge transfer resistance below 70 mV vs. Li/Li⁺ during charge, whereas there was its drastic diminishment between 0.2 and 0.5 V vs. Li/Li⁺ during discharge. Because these potential regions are each related to amorphous Li_xSi-to-Li₁₅Si₄ transition and vice versa, it could be shown that the formation and decomposition of Li₁₅Si₄ is responsible for the electrochemical degradation of Co–Co₃O₄ coated Si.     

Raman spectroscopy investigation on (Pb1−xLax)(Zr0.90Ti0.10)1−x/4O3 ceramic system

A Raman spectroscopy study at room temperature was carried out on (Pb_1−xLa_x)(Zr_0.90Ti_0.10)_1−x/4O₃ ceramics (x = 2, 3, 4 at%). The results were analyzed considering the x-ray patterns at room temperature showing a mixture of two phases: a rombohedral-ferroelectric phase and an orthorhombic-antiferroelectric, increasing the% of the second one with the lanthanum concentration. For x = 3 at%, the analysis was also carried out in a wide temperature range. Two anomalies were evaluated, one around 363 K, which has been associated to a ferroelectric-antiferroelectric phase transition; the second one around 430 K, which has been associated to a transition from an incommensurable state to a ferroelectric phase.     

Achieving high-rate capacitance of multi-layer titanium carbide (MXene) by liquid-phase exfoliation through Li-intercalation

The stacks of multi-layer Ti₃C₂T_x and other types of MXene materials limit their electrochemical performance. Herein, we report a facile exfoliation technique to improve the exfoliation efficiency through Li-intercalation into Ti₃C₂T_x interlayers in isopropyl alcohol (IPA) with LiOH as intercalant. This de-intercalation method presented here not only effectively delaminates the stacked Ti₃C₂T_x multi-layers into separate few-layer MXene sheets, but also achieves high-rate supercapacitive performance of Ti₃C₂T_x electrode. The as-produced delaminated Ti₃C₂T_x shows highly improved electrochemical capacitive properties from 47 to 115 F g^− 1 at 200 mV s^− 1. Even at extremely high scan rate of 1000 mV s^− 1, a specific capacitance of 82 F g^− 1 is still obtained. The high-rate capability can be attributed to improved ions accessibility into the few-layer structures. This study offers a new and simple exfoliation pathway for MXenes materials to exploit their full potential in energy storage applications.     

Crystal structures,site occupations and phase equilibria in the system V–Zr–Ge

The V–Zr–Ge system was studied for two isothermal sections at 900 and 1200 °C. Three ternary compounds VZrGe (tI12, I4/mmm, CeScSi-type), V_xZr_5?xGe₄ (oP36, Pnma, Sm₅Ge₄-type) and V_4+xZr_2?xGe₅ (oI44, Ibam, Si₅V₆-type) were structurally characterized. Optical microscopy and powder X-ray diffraction (XRD) were used for initial sample characterization and electron probe microanalysis (EPMA) of the annealed samples was used to determine the exact phase compositions. The variation of the cell parameters of the various ternary solid solutions with the composition was determined. The three ternary phases were structurally characterized by means of single crystal and powder XRD. While VZrGe is almost a line compound, V_xZr_5?xGe₄ (0.2 ≤ x ≤ 3.0) and V_4+xZr_2?xGe₅ (0.06 ≤ x ≤ 1.2) are forming extended solid solution ranges stabilized by differential fractional site occupancy of V and Zr on the metal sites.     

Temporal evolution study of the plasma induced by CO2 pulsed laser on targets of titanium oxides

This paper reports studies on time-resolved laser induced breakdown spectroscopy (LIBS) of plasmas induced by IR nanosecond laser pulses on the titanium oxides TiO and TiO₂ (anatase). LIBS excitation was performed using a CO₂ laser. The laser-induced plasma was found strongly ionized yielding Ti⁺, O⁺, Ti^2 +, O^2 +, Ti^3 +, and Ti^4 + species and rich in neutral titanium and oxygen atoms. The temporal behavior of specific emission lines of Ti, Ti⁺, Ti^2 + and Ti^3 + was characterized. The results show a faster decay of Ti^3 + and Ti^2 + ionic species than that of Ti⁺ and neutral Ti atoms. Spectroscopic diagnostics were used to determine the time-resolved electron density and excitation temperatures. Laser irradiation of TiO₂-anatase induces on the surface sample the polymorphic transformation to TiO₂-rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy.     

Structural investigation and electron paramagnetic resonance of vanadyl doped alkali niobium borate glasses

Glasses with compositions xNb₂O₅·(30 ? x)M₂O·69B₂O₃ (where M = Li, Na, K; x = 0, 4, 8 mol%) doped with 1 mol% V₂O₅ have been prepared using normal melt quench technique. The IR transmission spectra of the glasses have been studied over the range 400–4000 cm^?1. The changes caused by the addition of Nb₂O₅ on the structure of these glasses have been reported. The electron paramagnetic resonance spectra of VO²⁺ ions in these glasses have been recorded in X-band (9.14 GHz) at room temperature (300 K). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) due to V⁴⁺ ions which exist as VO²⁺ ions in octahedral coordination with a tetragonal compression in the present glasses. The tetragonality of V⁴⁺O₆ complex decreases with increasing concentration of Nb₂O₅. The 3d_xy orbit contracts with increase in Nb₂O₅:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported.     

Thermodynamic properties of calcium titanates: CaTiO3, Ca4Ti3O10, and Ca3Ti2O7

The chemical potentials of CaO in two-phase fields (TiO₂ + CaTiO₃), (CaTiO₃ + Ca₄Ti₃O₁₀), and (Ca₄Ti₃O₁₀ + Ca₃Ti₂O₇) of the pseudo-binary system (CaO + TiO₂) have been measured in the temperature range (900 to 1250) K, relative to pure CaO as the reference state, using solid-state galvanic cells incorporating single crystal CaF₂ as the solid electrolyte. The cells were operated under pure oxygen at ambient pressure. The standard Gibbs free energies of formation of calcium titanates, CaTiO₃, Ca₄Ti₃O₁₀, and Ca₃Ti₂O₇, from their component binary oxides were derived from the reversible e.m.f.s. The results can be summarised by the following equations: CaO(solid) + TiO₂(solid) → CaTiO₃(solid), ΔG° ± 85/(J · mol^?1) = ?80,140 ? 6.302(T/K); 4CaO(solid) + 3TiO₂(solid) → Ca₄Ti₃O₁₀(solid), ΔG° ± 275/(J · mol^?1) = ?243,473 ? 25.758(T/K); 3CaO(solid) + 2TiO₂(solid) → Ca₃Ti₂O₇(solid), ΔG° ± 185/(J · mol^?1) = ?164,217 ? 16.838(T/K).The reference state for solid TiO₂ is the rutile form. The results of this study are in good agreement with thermodynamic data for CaTiO₃ reported in the literature. For Ca₄Ti₃O₁₀ Gibbs free energy of formation obtained in this study differs significantly from that reported by Taylor and Schmalzried at T = 873 K. For Ca₃Ti₂O₇ experimental measurements are not available in the literature for direct comparison with the results obtained in this study. Nevertheless, the standard entropy for Ca₃Ti₂O₇ at T = 298.15 K estimated from the results of this study using the Neumann–Koop rule is in fair agreement with the value obtained from low-temperature heat capacity measurements.     

Photo-luminescence studies of strontium barium niobate crystals doped with Cr3+ ions

This paper reports the photo-luminescence spectroscopic results of Strontium–Barium–Niobate, Sr_x,Ba_1−xNb₂O₅ (SBN, x = 0.61 for near congruent composition) crystals doped with Cr₂O, at cryogenic temperature (20 K). The experimental results reveal the need of re-assignment of the Cr³⁺ ions defect centres in this material. For first time, a broad emission band in the near infrared region centred at ca. 950 nm is reported. This emission band has micro-seconds decaytime constant and a FWHM band-width > 1700 cm⁻¹ and has been ascribed to the vibronically assisted ⁴T₂ → ⁴A₂ transition. A much narrower emission band centred at ca. 764 nm with milli-seconds decaytime constant and a FWHM band-width of ca. 170 cm⁻¹ is correlated to the ²E → ⁴A₂ radiative transition (R-line).     

Novel method for the preparation of carbon supported nano-sized amorphous ruthenium oxides for supercapacitors

Nanostructured amorphous RuO₂ · xH₂O/C composite materials are prepared via a modified sol–gel process using glycolic acid. The glycolate anion, which dissociates from glycolic acid at pH 7, behaves as a stabilizer by adsorbing onto the RuO₂ · xH₂O surface, thus resulting in particles with a size of about 2 nm. As evidenced by zeta potential measurements, the surface charge of RuO₂ · xH₂O becomes more electronegative as the amount of glycolic acid increases. After heat treatment at 160 ^oC to remove the stabilizer, RuO₂ · xH₂O/C is found to exhibit an amorphous structure. The specific capacitance of RuO₂ · xH₂O/C particles (40 wt% Ru) prepared in the presence of glycolic acid (0.3 g L⁻¹) is 462 F g⁻¹, which is 30% higher than that of the material prepared in the absence of glycolic acid. Both the nanosized particles and the amorphous structure mainly contribute to this increase in the specific capacitance.     

Quaternary (liquid + liquid) equilibria for (water + 2-propanol + 1,1-dimethylethyl methyl ether + diisopropyl ether) at the temperature 298.15 K

(Liquid + liquid) equilibrium tie-lines were measured for one ternary system {x₁H₂O + x₂(CH₃)₂CHOH + (1 − x₁ − x₂)CH₃C(CH₃)₂OCH₃} and one quaternary system {x₁H₂O + x₂(CH₃)₂CHOH + x₃CH₃C(CH₃)₂OCH₃ + (1 − x₁ − x₂ − x₃)(CH₃)₂CHOCH(CH₃)₂} at T = 298.15 K and P^∘ = 101.3 kPa. The experimental (liquid + liquid) equilibrium results were satisfactorily correlated by modified and extended UNIQUAC models both with ternary and quaternary parameters in addition to binary ones.     

Electrochemical and in-situ X-ray diffraction studies of Ti3C2Tx MXene in ionic liquid electrolyte

2D titanium carbide (Ti₃C₂T_x MXene) showed good capacitance in both organic and neat ionic liquid electrolytes, but its charge storage mechanism is still not fully understood. Here, electrochemical characteristics of Ti₃C₂T_x electrode were studied in neat EMI-TFSI electrolyte. A capacitive behavior was observed within a large electrochemical potential range (from − 1.5 to 1.5 V vs. Ag). Intercalation and de-intercalation of EMI⁺ cations and/or TFSI⁻ anions were investigated by in-situ X-ray diffraction. Interlayer spacing of Ti₃C₂T_x flakes decreases during positive polarization, which can be ascribed to either electrostatic attraction effect between intercalated TFSI⁻ anions and positively charged Ti₃C₂T_x nanosheets or steric effect caused by de-intercalation of EMI⁺ cations. The expansion of interlayer spacing when polarized to negative potentials is explained by steric effect of cation intercalation.     

Measurements of HmE and VmE for (propane + sulphurhexafluoride) in the near critical region

A flow mixing calorimeter followed by a vibrating-tube densimeter has been used to measure excess molar enthalpies H_m^E and excess molar volumesV_m^E of {xC₃H₈ +  (1  − x)SF₆}. Measurements over a range of mole fractionsx have been made at the pressure p =  4.30 MPa at eight temperatures in the rangeT =  314.56 K to 373.91 K, in the liquid region at p =  3.75 MPa andT =  314.56 K, in the two phase region at p =  3.91 MPa andT =  328.18 K, and in the supercritical region at p =  5.0 MPa andT =  373.95 K. The measurements are compared with results from the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on{xCO₂ +  (1  − x)C₂H₆} ,{xCO₂ +  (1  − x)C₂H₄} and{xCO₂ +  (1  − x)SF₆} reported previously.