Preparation and microstructural characterization of (Nd1−xGdx)2(Ce1−xZrx)2O7 solid solutions

(Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ (0 ≤ x ≤ 1.0) powders with an average particle size of 100 nm were synthesized with chemical-coprecipitation and calcination method, and were characterized by X-ray diffractometry and scanning electron microscopy. The sintering behaviour of (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ powders was studied by pressureless sintering at 1600–1700 °C for 10 h in air. The relative densities of (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ solid solutions increase with increasing the sintering temperature, and gradually decrease with increasing the content of neodymium and cerium at identical temperature levels. (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ solid solutions have a single phase of defect fluorite-type structure among all the composition combinations studied. The lattice parameters of (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ solid solutions agree well with the Vegard's rule.     

Combustion synthesis of (Ti1−xNbx)2AlC solid solutions from elemental and Nb2O5/Al4C3-containing powder compacts

Preparation of the (Ti_1−xNb_x)₂AlC solid solution (formed from the M_n+1AX_n or MAX carbides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is C) with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS). Nearly single-phase (Ti,Nb)₂AlC was produced through direct combustion of constituent elements. Due to the decrease of reaction exothermicity, the combustion temperature and reaction front velocity decreased with increasing Nb content of (Ti_1−xNb_x)₂AlC formed from the elemental powder compacts. In addition, the samples composed of Ti, Al, Nb₂O₅, and Al₄C₃ were adopted for the in situ formation of Al₂O₃-added (Ti,Nb)₂AlC. The SHS process of the Nb₂O₅/Al₄C₃-containing sample involved aluminothermic reduction of Nb₂O₅, which not only enhanced the reaction exothermicity but also facilitated the evolution of (Ti,Nb)₂AlC. Based upon the XRD analysis, two intermediates, TiC and Nb₂Al, were detected in the (Ti,Nb)₂AlC/Al₂O₃ composite and their amounts were reduced by increasing the extent of thermite reduction involved in the SHS process. The laminated microstructure characteristic of the MAX carbide was observed for both monolithic and Al₂O₃-added (Ti,Nb)₂AlC solid solutions synthesized in this study.     

Hydrogen evolution on RuxTi1−xO2 in 0.5 M H2SO4

Hydrogen evolution from 0.5 M H₂SO₄ on Ti electrodes coated with a Ru_xTi_1−xO₂ (x=0.04-0.5) layer has been studied by potentiostatic polarisation, cyclic voltammetry and ac-impedance spectroscopy. The results indicate that after a certain activation period the performance of such an electrode coating is comparable to platinum. The addition of small amounts of sodium molybdate increased the capacitance of the electrode and a reduction of the performance was observed. Increasing the temperature of the pure electrolyte from 20 to 75 °C caused an increase in the rate of the hydrogen evolution and in addition an increase of the electrode capacitance. The electrodes have been found to be rather tolerant to chloride and Fe²⁺ ions, and could hence be promising candidates as catalyst materials for solid polymer water electrolysis systems. From steady state measurements the Tafel slopes were found to change from −105 mV/decade for pure titanium to about −40 mV/decade for the (RuTi)O₂ coated electrodes. The exchange current densities were calculated from the steady state curves, as well as from impedance data, to be about 10⁻⁴ A cm⁻² after activation.     

A novel synthesis route to Sn1−xRExO2−x/2 nanorods via microwave-induced salt-assisted solution combustion process

Sn_1−xRE_xO_2−x/2 (RE=Y, La, Gd and Nd) nanorods have been prepared by annealing the as-obtained products from microwave-induced KCl-assisted solution combustion reaction. The phase evolution in the synthesis process was investigated by an X-ray diffractometer. Accordingly, the possible growth mechanism of Sn_1−xRE_xO_2−x/2 nanorods was discussed based on oriented attachment by polar forces. The results showed that the Sn_0.8Y_0.2O_1.9 nanorods were rutile-structured single crystals with 8–12 nm diameter and 100–200 nm length. Proper addition of KCl into the redox mixture solution is critical to the formation of Sn_1−xRE_xO_2−x/2 nanorods. The approach is convenient, inexpensive and efficient for the high yield preparation of Sn_1−xRE_xO_2−x/2 nanorods.     

Adjustable dielectric properties of Li2CuxZn1−xTi3O8 (x=0 to 1) ceramics with low sintering temperature

Single-phase dielectric ceramics Li₂Cu_xZn_1−xTi₃O₈ (x=0–1) were synthesized by the conventional solid-state ceramic route. All the solid solutions adopted Li₂MTi₃O₈ cubic spinel structure in which Li/M and Ti show 1:3 order in octahedral sites whereas Li and M are distributed randomly in tetrahedral sites with the degree of Li/M cation mixing varying from 0.5 to 0.3. The substitution of Cu for Zn effectively lowered the sintering temperatures of the ceramics from 1050 to 850 °C and significantly affected the dielectric properties. As x increased from 0 to 0.5, τ_f gradually increased while the dielectric constant (ε_r) and quality factor value (Q×f) gradually decreased, and a near-zero τ_f of 1.6 ppm/°C with ε_r of 25.2, Q×f of 32,100 GHz could be achieved for Li₂Cu_0.1Zn_0.9Ti₃O₈ ceramic sintered at 950 °C, which make it become an attractive promising candidate for LTCC application. As x increases from 0.5 to 1, the dielectric loss significantly increases with AC conductivity increasing up to 2.3×10⁻⁴ S/cm (at 1 MHz).     

Synthesis and negative thermal expansion property of Y2−xLaxW3O12 (0≤x≤2)

Y_2−xLa_xW₃O₁₂ solid solutions were successfully synthesized by the solid state reaction method. The microstructure, hygroscopicity and thermal expansion property of the resulting samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and thermal mechanical analysis (TMA). Results indicate that the structural phase transition of the Y_2−xLa_xW₃O₁₂ changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phase can form for 0≤x≤0.4 with orthorhombic structure and for 1.5≤x≤2 with monoclinic one. High lanthanum content leads to a low relative density of Y_2−xLa_xW₃O₁₂ ceramic. Thermal expansion coefficients of the Y_2−xLa_xW₃O₁₂ (0≤x≤2) ceramics also vary from −9.59×10⁻⁶ K⁻¹ to 2.06×10⁻⁶ K⁻¹ with increasing substituted content of lanthanum. The obtained Y_0.25La_1.75W₃O₁₂ ceramic shows almost zero thermal expansion and its average linear thermal expansion coefficient is −0.66×10⁻⁶ K⁻¹ from 103 °C to 700 °C.     

Phase transition and negative thermal expansion properties of Sc2−xCrxMo3O12

The crystal structure, phase transition and thermal expansion behaviors of solid solutions Sc_2−xCr_xMo₃O₁₂ (0≤x≤2) were investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). At room temperature, samples with x≤0.7 and x≥0.8 crystallize in orthorhombic and monoclinic structures, respectively. DSC result indicates that the phase transition of Sc_0.5Cr_1.5Mo₃O₁₂ from monoclinic to orthorhombic structure occurs at 203.66 °C. The linear thermal expansion coefficient of orthorhombic phases varies from −2.334×10⁻⁶ °C⁻¹ to 0.993×10⁻⁶ °C⁻¹ when x increases from 0.0 to 1.5. The near-zero linear thermal expansion coefficients of −0.512×10⁻⁶ °C⁻¹ and −0.466×10⁻⁶ °C⁻¹ are observed for compounds with x=0.5 and 0.7, respectively.     

Amorphous LiCoO2 thin films on Li1+x+yAlxTi2−xSiyP3−yO12 prepared by radio frequency magnetron sputtering for all-solid-state Li-ion batteries

Amorphous LiCoO₂ thin films were deposited on the NASICON-type glass ceramics, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATSP), by radio frequency (RF) magnetron sputtering below 180 °C. The as-deposited LiCoO₂ thin films were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscope. All-solid-state Li/PEO₁₈-Li (CF₃SO₂)₂N/LATSP/LiCoO₂/Au cells were fabricated using the amorphous film. The electrochemical performance of the cells was investigated by galvanostatic cycling, cyclic voltammetry, potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. It was found that the amorphous LiCoO₂ thin film shows a promising electrochemical performance, making it a potential application in microbatteries for microelectronic devices.     

Effects of B-site ion (M) substitution on the ionic conductivity of (Li3xLa2/3−x)1+y/2(MyTi1−y)O3 (M=Al, Cr)

Effect on the ionic conductivity of B-site ion (M) substitution in (Li_3xLa_2/3−x)_1+y/2M_yTi_1−yO₃ (M=Al, Cr) has been investigated. It has been found that partial substitution of smaller Al³⁺ for Ti⁴⁺ is effective to enhance the ionic conductivity of Li_3xLa_2/3−xTiO₃. At 300 K, the maximum bulk conductivity of (1.58±0.01)×10⁻³ S cm⁻¹ is observed from the composition of (Li_0.39La_0.54)_1−y/2Al_yTi_1−yO₃ with y=0.02 (x=0.13), that is the highest yet reported for known perovskite solutions at room temperature. The conductivity enhancement is interpreted as being due to the substitution-induced bond-strength change rather than due to bottleneck size change for Li migration, TiO₆-octahedron tilting or A-site cation ordering.     

Effect of boron on the structural and electrochemical properties of nanocrystalline Ti2RuFeBx electrodes

The effect of the boron content on the structural and electrochemical properties of nanocrystalline Ti₂RuFeB_x (with x varying from 0 to 12) was studied. The nanocrystalline materials were prepared by high energy ball milling and their structural evolution was analyzed by X-ray and neutron diffraction. Through a detailed Rietveld refinement analysis of the structural data, it is shown that the nanocrystalline materials are mainly composed of a B2 structure at low boron content (0 < x < 2). At higher boron content, TiB₂ is mainly formed and the B2 structure disappears with the concurrent formation of a highly disordered Ru-rich phase. These electrodes were tested for the hydrogen evolution reaction in both NaOH and chlorate solutions. The best results are obtained for 4 ≤ x ≤ 6, with a cathodic overpotential at −250 mA/cm², η₂₅₀, of ∼−575 mV. Accelerated aging tests and continuous electrolysis tests show that η₂₅₀ does not vary with time, contrary to the case of Ti₂RuFe, which shows a rapid deterioration of the cathodic overpotential after a few hours of continuous electrolysis. This is explained by the lower solubility of hydrogen in Ti₂RuFeB₄ as opposed to Ti₂RuFe.     

Raman and dielectric investigation of (Ba0.9−xSrxCa0.1)(Ti0.8Zr0.2)O3 ferroelectric ceramics

Solid solutions of (Ba_0.9−xSr_xCa_0.1)(Ti_0.8Zr_0.2)O₃ (BSCTZ) (0.1≤x≤0.4) were prepared using the conventional solid state reaction method. The effects of the substitution content on the crystallographic structure, phase transition and dielectric properties of the samples were investigated by dielectric and Raman spectroscopy over a wide temperature range from 100 to 500 K. All the samples were noted to undergo a diffuse phase transition from the tetragonal to the cubic phase and to exhibit a relaxor ferroelectric behavior.     

Effect of La substitution on the structural and electrical properties of BaBi4−xLaxTi4O15

Pure and lanthanum doped barium bismuth titanate BaBi_4−xLa_xTi₄O₁₅ (BBLT, x=0, 0.05, 0.15, 0.30) ceramics were prepared utilizing solid state method. The X-ray diffraction (XRD) data confirmed formation of single-phase Aurivillius compounds while SEM micrographs did not show evident grain size change of doped ceramics. Dielectric properties were investigated in 1.21 kHz to 1 MHz frequency range and in the temperature range of 20 to 727 °C. When Bi³⁺ is substituted with La³⁺, a significant disorder was induced and the material exhibited broadening of the phase transition. Impedance analysis confirmed the presence of two semicircular arcs in doped samples suggesting the existence of grain and grain-boundary conduction. The dc-conductivity and activation energies were evaluated for all compositions.     

Enhanced ferroelectric properties in (Ba1−xCax)(Ti0.94Sn0.06)O3 lead-free ceramics

Lead-free (Ba_1−xCa_x)(Ti_0.94Sn_0.06)O₃ (BCST) (x = 0.01-0.04) ceramics were prepared using a solid-state reaction technique. The effects of Ca content on the phase structure and electrical properties of the BCST ceramics were investigated. High piezoelectric coefficient of d₃₃ = 440 pC/N, planar electromechanical coupling factor of k_p = 45% and dielectric constant ?_r = 6900 were obtained for the samples at x = 0.03. At room temperature, a polymorphic phase transition (PPT) from orthorhombic phase to tetragonal phase was identified in the composition range of 0.02 < x < 0.04.     

Nano-structured PdxPt1−x/Ti anodes prepared by electrodeposition for alcohol electrooxidation

Nano-structured Pd_xPt_1−x (x = 0-1) composite catalysts supported on Ti substrate are successfully prepared by electrodeposition method, and the morphology and phase of the catalysts are analyzed by field emission scanning electron microscope (FE-SEM) and X-ray energy dispersion spectroscopy (EDS). The activity and stability of the Pd_xPt_1−x/Ti composite catalysts are assessed for the electrooxidation of alcohols (methanol, ethanol and 2-propanol) in alkaline medium using cyclic voltammetry and chronoamperometry techniques. The results show that the Pd and Pt form Pd_xPt_1−x nano-structured composite catalysts, uniformly distributed on the Ti substrate. The electrocatalytic activity and stability of the Pd_xPt_1−x nanocatalysts depend strongly on the atomic ratios of Pd and Pt. Among the synthesized catalysts, the Pd_0.8Pt_0.2/Ti displays the best catalytic activity and stability for the electrooxidation reaction of alcohols investigated in alkaline medium under conditions in this study, and shows the potential as electrocatalysts for direct alcohol fuel cells.     

Synthesis and tunable thermal expansion properties of Sc2−xYxW3O12 solid solutions

A new series of rare earth solid solutions Sc_2−xY_xW₃O₁₂ was successfully synthesized by the conventional solid-state method. Effects of doping ion yttrium on the crystal structure, morphology and thermal expansion property of as-prepared Sc_2−xY_xW₃O₁₂ ceramics were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TG), field emission scanning electron microscope (FE-SEM) and thermal mechanical analyzer (TMA). Results indicate that the obtained Sc_2−xY_xW₃O₁₂ samples with Y doping of 0≤x≤0.5 are in the form of orthorhombic Sc₂W₃O₁₂-structure and show negative thermal expansion (NTE) from room temperature to 600 °C; while as-synthesized materials with Y doping of 1.5≤x≤2 take hygroscopic Y₂W₃O₁₂·nH₂O-structure at room temperature and exhibit NTE only after losing water molecules. It is suggested that the obvious difference in crystal structure leads to different thermal expansion behaviors in Sc_2−xY_xW₃O₁₂. Thus it is proposed that thermal expansion properties of Sc_2−xY_xW₃O₁₂ can be adjusted by the employment of Y dopant; the obtained Sc_1.5Y_0.5W₃O₁₂ ceramic shows almost zero thermal expansion and its average linear thermal expansion coefficient is −0.00683×10⁻⁶ °C⁻¹ in the 25–250 °C range.     

Characterization of Mg1−xNixAl2O4 solid solutions prepared by combustion synthesis

Mg_1−xNi_xAl₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) solid solutions have been prepared by combustion synthesis. After annealing the combustion synthesized powders at 1000 °C for 3 h single-phase Mg_1−xNi_xAl₂O₄ was obtained over the entire range of compositions. The lattice parameter of Mg_1−xNi_xAl₂O₄ gradually increased from 8.049 Å (NiAl₂O₄) to 8.085 Å (MgAl₂O₄), which certified the formation of the spinel solid solutions. All samples prepared by combustion synthesis had blue color shades, denoting the inclusion of Ni²⁺ in the spinel structure in octahedral and tetrahedral configuration. The crystallite size of Mg_1−xNi_xAl₂O₄ was in the range of 35-39 nm and the specific surface area varied between 5.8 and 7.0 m²/g.     

Electrochemical hydrogen storage in (Ti1−xVx)2Ni (x = 0.05-0.3) alloys comprising icosahedral quasicrystalline phase

For (Ti_1−xV_x)₂Ni (x = 0.05, 0.1, 0.15, 0.2 and 0.3) ribbons, synthesized by arc-melting and subsequent melt-spinning techniques, an icosahedral quasicrystalline phase was present, either in the amorphous matrix or together with the stable Ti₂Ni-type phase. With increasing x values, the maximum discharge capacity of the alloy electrodes increased until reached 271.3 mAh/g when x = 0.3. The cycling capacity retention rates for these electrodes were approximately 80% after a preliminary test of 30 consecutive cycles of charging and discharging. Ti_1.7V_0.3Ni alloy electrode displayed the best high-rate discharge ability of 82.7% at the discharge current density of 240 mA/g.     

Preparation and characterization of novel spinel Li4Ti5O12−xBrx anode materials

Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) materials were investigated. The Li₄Ti₅O_12−xBr_x (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂, especially at high current rates. When the discharge rate was 0.5 C, the Li₄Ti₅O_12−xBr_x (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g⁻¹, which was very close to its theoretical capacity (175 mAh g⁻¹), while that of the pristine Li₄Ti₅O₁₂ was 123.2 mAh g⁻¹ only.     

Structural and dielectric properties of Bi1−xSrxMnO3 (0.40≤x≤0.55)

In order to study the effect of Sr substitution on structural and dielectric properties of Bi_1−xSr_xMnO₃ (0.40≤x≤0.55) compounds were synthesized by the solid state reaction method. The as-prepared samples were characterized by X- ray diffraction (XRD) and dielectric measurements to correlate structural changes with dielectric properties. The XRD data were further analyzed by the Rietveld refinement. The highest dielectric constant was observed in Bi_0.55Sr_0.45MnO₃ and Bi_0.5Sr_0.5MnO₃ systems (∼10⁶) mainly because of orientation polarization. The charge ordering temperature decreases with increasing Sr concentration in Bi_1−xSr_xMnO₃ systems.