Preparation and characterization of new visible-light-driven BaCo0.5Nb0.5O3 photocatalyst

A new type of visible-light-driven photocatalyst BaCo_0.5Nb_0.5O₃ was successfully synthesized via a sol-gel process in this study. After heating the precursors at 1000 °C, a pure perovskite phase was obtained. The particle size and crystallinity of BaCo_0.5Nb_0.5O₃ powders markedly increased with a rise in the calcination temperature. The band gap of BaCo_0.5Nb_0.5O₃ calculated from the UV-visible spectra was found to be less than that of titania. BaCo_0.5Nb_0.5O₃ was demonstrated to have photocatalytic activity under visible light irradiation and this activity significantly depended on the synthesis temperature. The sol-gel derived powders were found to have better photocatalytic activity than the solid-state derived powders because of the reduced particle size and increased surface area.     

Nanostructured GdAlO3 perovskite, a new possible catalyst for combustion of volatile organic compounds

The purpose of this paper was to obtain nanosize GdAlO₃ perovskite powders for catalyst applications. Two different thermal treatments (900 °C for 1 h and 1000 °C for 7 h) were applied to amorphous powder obtained by combined sol–gel and self-combustion method to promote crystallization of GdAlO₃ perovskite. The structural and phase transformations after each thermal treatment have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ adsorption. After treatment at 900 °C the formation of perovskite phase, GdAlO₃ (with orthorhombic structure) in mixture with other phases (Gd₂O₃, Al₂O₃, Gd₄Al₂O₉, and Gd₃Al₅O₁₂) was detected. A monophase crystalline material, GdAlO₃ pure perovskite, with crystallite size of 40 nm and S_BET of 10 m²/g was obtained after a longer treatment, 7 h at 1000 °C. The catalytic activity of the two nanocrystalline samples in the combustion reaction of acetone, propane, benzene, and Pb free gasoline was studied. Both samples exhibit the best catalytic activity for acetone combustion (80 % acetone conversion at 500 °C) and proved poor catalytic performance in catalytic combustion of Pb free gasoline (24 % conversion at 500 °C). Although S_BET value for sample treated at 900 °C is higher (22 m²/g) than that of the sample treated at 1000 °C (10 m²/g), the treatment at 1000 °C for 7 h assures a good thermo-chemical stability of GdAlO₃ perovskite required by low temperature catalyst applications. GdAlO₃ perovskite seems to be a promising catalyst for low temperature acetone combustion (T < 500 °C).     

Microstructure, dielectric and piezoelectric properties of La-modified Bi0.5(Na0.84K0.16)0.5TiO3 lead-free ceramics

Lead-free ceramics (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ were prepared by a conventional ceramic technique and the effects of La doping and sintering temperature on the microstructure, ferroelectric and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and La³⁺ diffuses into the Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ lattices to form a solid solution with a rhombohedral symmetry. The addition of La leads to the significant change in the grain morphology and size for the (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ and a number of rod grains with the length of 10–50 μm and the diameter of 1–2 μm are observed in the ceramic with x = 0.04 sintered at 1,140 °C for 2 h. However, as sintering temperature increases to 1,160 °C, the rod grains disappears and the uniform and rectangular grains are observed in the ceramics with x = 0.04. As x increases from 0 to 0.06, the coercive field E _c of the ceramics decreases from 4.33 to 2.81 kV/mm and the remanent polarization P _r of the ceramics retains the high values of 25.9–27.7 μm/cm². The depolarization temperature T _d decreases from 154 to 50 °C with x increasing from 0 to 0.10. All the ceramics exhibit the diffusive phase transition at high temperature (280–320 °C). The ceramic with x = 0.04 sintered at 1,150 °C for 2 h exhibit the optimum piezoelectric properties, giving d ₃₃ = 165 pC/N and k _p = 32.9 %. The optimum sintering temperature is 1,150 °C at which the improved piezoelectric properties (d ₃₃ = 165 pC/N and k _p = 32.9 %) are obtained. At the high La³⁺ level (x = 0.10 and 0.12), the ceramics exhibit weak ferroelectricity (P _r = 13.0–21.2 μm/cm²) and thus possess poor piezoelectricity (d ₃₃ = 17–27 pC/N).     

Synthesis of fine Pb(Fe0.5Nb0.5)O3 perovskite powders by coprecipitation method

Lead iron niobate, Pb(Fe_0.5Nb_0.5)O₃ (PFN) is an optimal material for multilayered ceramic capacitors (MLCCs). Fine lead iron niobate powders with average size of 500 nm were prepared from the precipitation precursor. In the experiment, Nb₂O₅ was used as Nb source to substitute Nb alkyloxide or oxalate and successfully converted into aqueous Nb⁵⁺ solution. The results shows that the perovskite PFN was emerged at a temperature as low as 400 °C, and pure perovskite was obtained at the temperature of 800 °C. The formation of perovskite at a low temperature was attributed to the core–shell structure in the precipitates of hydroxide. Besides, the particles of perovskite PFN show the good chemical stoichiometry and small size of 300–500 nm.     

Synthesis and Magnetic Properties of L0.5Sr0.5Mn0.5M0.5O3 (L = Y, Pr; M = Cu, Ru)

A new Mn-containing material with nominal composition L_0.5Sr_0.5Mn_0.5M_0.5O₃ (L = Y or Pr; M = Cu or Ru), as well as Y_0.5Sr_0.5MnO₃ for comparison, were synthesized. The results of the XRD and EDX analyses show that the obtained samples are single-phased and isostructural, with L_1–xA_xMnO₃. The L_0.5Sr_0.5Mn_0.5Cu_0.5O₃ material displays a PM behavior down to 8 K where paramagnetic–antiferromagnetic transition begins. The Pr_0.5Sr_0.5Mn_0.5Cu_0.5O₃ sample has a broad transition at 210 K and a magnetoresistance of 34% at 128 K. The Pr_0.5Sr_0.5Mn_0.5Ru_0.5O₃ material has a paramagnetic–ferromagnetic transition beginning at 330 K and a ferromagnetic–antiferromagnetic one at about 160 K. The obtained value of T _c is the highest for the Pr-containing manganites. The roles of Pr/Sr ratio, anisotropy, and intergranular effects in the samples are discussed.     

The effects of quenching treatment and AlF3 coating on LiNi0.5Mn0.5O2 cathode materials for lithium-ion battery

Submicron layered LiNi_0.5Mn_0.5O₂ was synthesized via a co-precipitation and solid-state reaction method together with a quenching process. The crystal structure and morphology of the materials were investigated by X-ray diffraction (XRD), Brunauer–Emmett and Teller (BET) surface area and scanning electron microscopy (SEM) techniques. It is found that LiNi_0.5Mn_0.5O₂ material prepared with quenching methods has smooth and regular structure in submicron scale with surface area of 0.43 m² g⁻¹. The initial discharge capacities are 175.8 mAh g⁻¹ at 0.1 C (28 mA g⁻¹) and 120.3 mAh g⁻¹ at 5.0 C (1400 mA g⁻¹), respectively, for the quenched samples between 2.5 and 4.5 V. It is demonstrated that quenching method is a useful approach for the preparation of submicron layered LiNi_0.5Mn_0.5O₂ cathode materials with excellent rate performance. In addition, the cycling performance of quenched-LiNi_0.5Mn_0.5O₂ material was also greatly improved by AlF₃ coating technique.     

Preparation and Properties of Al2O3-doping LiNi1/3Co1/3Mn1/3O2 Cathode Materials

LiNi_1/3Co_1/3-xMn_1/3O₂ doped with Al₂O₃ (x = 0%, 2.5%, 5%, 10%) was synthesized by co-precipitation of Ni, Co, and Mn acetates. The influence of Al₂O₃ doping on structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ was studied using X-ray diffraction (XRD) analysis, scanning electron microscopy, charge/discharge tester, and electrochemical workstation. It was found that the materials achieved the best electrochemical properties when x was 5%. The first discharge capacity was 156.3 mAh · g^?1(0.1 C, 2.0–4.8 V), which was close to the un-doped sample (156.8 mAh · g^?1). After 20 cycles, the capacity retention ratios at the C-ratios of 0.1C, 0.2C, and 0.5 C were 96.1%, 94.9%, and 89.4%, respectively, while the capacity retention ratios of the un-doped samples were only 92.6% (0.1 C), 91.8% (0.2 C), and 88.7% (0.5C). The alternating current impedance shows that the charge transfer in the electrode interface was the easiest when x was 5%.     

Epitaxial growth and thermoelectric properties of TiNiSn and Zr0.5Hf0.5NiSn thin films

Due to their exceptional thermoelectric properties Half-Heusler alloys like MNiSn (M = Ti,Zr,Hf) have moved into focus. The growth of single crystalline thin film TiNiSn and Zr_0.5Hf_0.5NiSn by dc magnetron sputtering is reported. Seebeck and resistivity measurements were performed and their dependence on epitaxial quality is shown. Seebeck coefficient, specific resistivity and power factor for Zr_0.5Hf_0.5NiSn at room temperature were measured to be 63 μV K^− 1, 14.1 μΩ m and 0.28 mW K^− 2 m^− 1, respectively. Multilayers of TiNiSn and Zr_0.5Hf_0.5NiSn are promising candidates to increase the thermoelectric figure-of-merit by decreasing thermal conductivity perpendicular to the interfaces. The epitaxial growth of multilayers containing TiNiSn and Zr_0.5Hf_0.5NiSn is demonstrated by measuring satellite peaks in the X-ray diffraction pattern originating from the additional symmetry perpendicular to the film surface.     

Compositional effects on the properties of (1-x)BaTiO3-xBi0.5Na0.5TiO3 ceramics

The compositional effects on the crystal structure, phase transition, dielectric, ferroelectric and piezoelectric properties of the (1-x)BaTiO₃-x(Bi_0.5Na_0.5)TiO₃ solid solution ceramics were investigated. After sintering at 1200 °C for 2 h, the ceramics with different content of (Bi_0.5Na_0.5)TiO₃ (BNT) formed single-phase solid solutions with perovskite structure. The lattice constant c/a ratio of the solid solutions decreased as BNT content increased except that with 20 mol% BNT, which had the largest value of c/a ratio for all samples. The second phase transition corresponding to BaTiO₃ (BT) at about 5 °C shifted to low temperature and gradually disappeared as BNT increased. A new secondary phase transition appeared at 32 °C and 64 °C, respectively, when BNT content was 5 and 14 mol%. The Curie temperature, T _c, shifted in the temperature range between 112 °C and 166 °C, and the remanent polarization, P _r, decreased whereas the coercive field, E _c, increased as the BNT content increased. The relatively high value of piezoelectric coefficient d₃₃ together with a relatively high Curie temperature and low loss tangent and stable dielectric properties were obtained when the addition of BNT was 20 mol%.     

Microstructure,ferroelectric, piezoelectric and ferromagnetic properties of BiFeO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 lead-free multiferroic ceramics

Multiferroic ceramics of (0.70?x)BiFeO₃–0.30BaTiO₃–xBi(Zn_0.5Ti_0.5)O₃ + 1 mol% MnO₂ with perovskite structure were prepared by a conventional ceramic technique and the effects of Bi(Zn_0.5Ti_0.5)O₃ doping and sintering temperature on the microstructure, multiferroic and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and no second phases can be detected. After the addition of a small amount of Bi(Zn_0.5Ti_0.5)O₃ (x ≤ 0.05), the ferroelectric and piezoelectric properties of the ceramics are improved and the grain growth is promoted. However, excess Bi(Zn_0.5Ti_0.5)O₃ (x ≥ 0.10) retards the grain growth, degrades the ferroelectricity and piezoelectricity, and induces two dielectric anomalies at high temperature. The ceramics can be well sintered at the very wide range of low sintering temperatures (880–980 °C) and exhibit good densification (relative density: 96.2–98.4 %) and strong electric insulation. The increase in the sintering temperature promotes the grain growth and improves the ferroelectricity of the ceramics. The ceramic with x = 0.05 sintered at 880–980 °C possesses improved ferroelectric and piezoelectric properties with remanent polarizations P _r of 21.9–28.1 μm/cm², piezoelectric constants d ₃₃ of 125–139 pC/N and planar electromechanical coupling factors k _p of 30.1–32.4 %, and high Curie temperatures T _C of 523–565 °C. A weak ferromagnetism with remanent magnetizations M _r of 0.0411–0.0422 emu/g and coercive fields H _c of 1.70–1.99 kOe were observed in the ceramics with x = 0–0.025.     

Effects of hot pressing temperature on microstructure,hardness and corrosion resistance of Al2NbTi3V2Zr high-entropy alloy

A novel lightweight high-entropy alloy Al₂NbTi₃V₂Zr was fabricated by vacuum hot pressing. The effects of sintering temperature (1200–1550°C) on the microstructure, hardness and corrosion resistance of the alloy were investigated. Results showed that Al₂NbTi₃V₂Zr mainly consisted of simple cubic matrix and (Zr, Al)-based intermetallic phase (α-phase) at sintering temperatures of 1200–1350°C. Moreover, the matrix phase transformed from simple cubic to body-centred cubic phase, and (Ti, Zr, Al)-based intermetallic precipitated from the matrix at temperature of 1450°C. The fabricated Al₂NbTi₃V₂Zr alloy had low density of 5.05–5.23?g?cm^–3, high hardness of 510–728?HV and excellent corrosion resistance in 10?wt-% HNO₃ solution.     

Kinetic Properties of Orientational Phase Transition in Polymerized States of Fullerites C60

Abstract

In the present work, we have shown that at early stages of dimerization, which occur during synthesis of C₆₀ fullerite T _syn = 10–40°C and P _syn = 1.5–8 GPa, kinetics of the sc→fcc phase transition, may be well described by Avrami law with Avrami's exponent n _Avr = 3 (i.e., in this case we are dealing with martensite‐like transformation). Fullerite's samples produced at higher temperatures (40°C < T _syn < 120°C) exhibit different kinetics with lower Avrami‐exponent. This behavior we attribute to the transformation switching to diffusion‐controlled kinetics.     

Synthesis,microstructure, and electrical behavior of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> piezoelectric ceramics via a citric acid sol–gel method

Nanosize (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ precursor powders were prepared via the citric acid sol–gel method. The ceramics were sintered at 1100–1150 °C. All ceramics exhibit a single-phase perovskite structure. With increasing sintering temperature, the average size of grains in the samples changes slightly from 0.3 to 0.5 µm. All ceramics show obvious dielectric dispersion. Activation energy values were obtained via impedance, electric modulus, and conductivity, respectively, which are in the range of 0.60–1.06 eV. Compared to ceramics synthesized by solid-state reaction method, the as-synthesized samples are fine-grained and have high depolarization temperature and excellent temperature stability of the piezoelectric constant (d ₃₃). The d ₃₃ value of the sample sintered at 1120 °C remains as high as 119 pC N^?1 with increasing annealing temperature to 115 °C, whereas the reduced amplitude of d ₃₃ is only approximately 3%.     

Synthesis of Na0.5Bi0.5TiO3 anisotropic particles with grain orientation by conversion of Na0.5Bi4.5Ti4O15 crystals

A novel method for synthesizing Na_0.5Bi_0.5TiO₃ (BNT) anisotropic particles with grain orientation is reported. Anisotropically shaped particles of BNT were prepared by conversion of Na_0.5Bi_4.5Ti₄O₁₅ (NBT15) single crystals. Platelet NBT15 was produced by molten-salt synthesis. They were converted to BNT by second molten-salt synthesis at 800–1200 °C. NBT15 single-crystal platelets were transformed into platelet particles of polycrystalline BNT. The reaction is topotaxial, those recrystallized BNT were oriented with (h 0 0) plane parallel to the platelet. The use of converted BNT particles as seed was confirmed by performing templated grain growth (TGG) of BNT with 5% grain-oriented, anisotropic particles of BNT.     

Pb(Zr0.5, Ti0.5)O3 nanofibres by electrospinning

Lead zirconate titanate Pb(Zr_0.5, Ti_0.5)O₃ nanofibres with diameters ranging from 200–300 nm have been synthesized by calcination of the electrospun lead zirconate titanate/polyvinyl acetate composite fibres. The morphology and crystalline phase features of these lead zirconate titanate (PZT) nanofibres have been studied by various physico-chemical methods such as SEM, AFM, XRD and FT–IR. The formation of perovskite PZT phase was observed at temperatures as low as 550 °C.     

Preparation and piezoelectric properties of CuO-doped (Na0.5K0.5)NbO3 ceramics by the citrate precursor method

A low-cost citrate so-gel route was investigated to synthesize nano-sized crystalline powders (<100 nm) of 1 mol% CuO modified (Na_0.5K_0.5)NbO₃ compositions. It was found that amorphous gels can be transformed into crystallite powders with single-phase perovskite structure when calcined at 500?C600 °C for 3 h. The transmission electron microscopy observation showed that the particles are column-like and well dispersed, depending on the calcination condition. The as-pressed samples exhibit improved densification behavior and finer grain morphology after sintering. Electrical properties of the samples sintered at 1,060 °C are as follows: dielectric constant ?? _r  = 605, piezoelectric constant d ₃₃ ~ 117 pC/N, planar electromechanical coupling factor k _p  ~ 0.38 and mechanical quality factor Q _m  ~ 725.     

Magnetic,optical, dielectric,and sintering properties of nano-crystalline BaFe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> synthesized by a polymerization method

A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe_0.5Nb_0.5O₃ is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe_0.5Nb_0.5O₃ powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative density ≥ 90%) can be obtained either after conventional sintering above 1250 °C for 1 h or after two-step sintering at 1200 °C. Depending on the sintering regime, the ceramics have average grain sizes between 0.3 and 52 µm. The optical band gap of the nano-sized powder is 2.75(4) eV and decreases to 2.59(2) eV after sintering. Magnetic measurements of ceramics reveal a Néel temperature of about 23 K. A weak spontaneous magnetization might be due to the presence of a secondary phase not detectable by XRD. Dielectric measurements show that the permittivity values increase with decreasing frequency and rising temperature. The highest permittivity values of 10.6 × 10⁴ (RT, 1 kHz) were reached after sintering at 1350 °C for 1 h. Tan δ values of all samples show a maximum at 1–2 MHz at RT. The frequency dependence of the impedance can be well described using a single RC-circuit.     

Structural,Thermal, and Electrical Study of Bi0.5Sr0.5MnO3

Solid oxide fuel cell (SOFC) is considered as a potential candidate for clean and efficient alternate energy source. Efforts are being made to reduce their operating temperature for SOFCs commercialization. However, the reduction in operating temperature increases the polarization effect in the existing cathodes. In the present study, Bi_0.5Sr_0.5MnO₃ was synthesized and studied for its structural, thermal, and electrical properties. Bi_0.5Sr_0.5MnO₃ was synthesized by conventional solid state reaction method. The as-prepared sample was characterized by x-ray diffraction, scanning electron microscope, thermogravimetric analysis, dilatometer and impedance spectroscopy. The Rietveld refinement results confirm that Bi_0.50Sr_0.50MnO₃ shows the tetragonal symmetry with p4 mm space group. Scanning electron microscopy study shows that the distribution of grains is uniform and the grains are well connected to each other due to better sinterability of the samples. The dilatometric curve shows linear behavior up to 600°C and after that becomes steeper. This can be due to the loss of lattice oxygen at higher temperatures and creation of oxygen vacancies. The thermal expansion coefficient of the system is ～8.9 × 10^?6 °C^?1 and total conductivity of the sample is ～4.78 × 10^?3 S/cm.     

Structure and electrical properties of Bi0.5Na0.5TiO3-Y0.5Na0.5TiO3-BaTiO3 lead-free piezoelectric ceramics

New (1 – x ? y)Bi_0.5Na_0.5TiO₃-xY_0.5Na_0.5TiO₃-yBaTiO₃ lead-free ceramics have been prepared by a conventional ceramic fabrication technique, and their structure and electrical properties have been studied. A morphotropic phase boundary (MPB) of rhombohedral and tetragonal phases is formed at 0.04 < y < 0.10. As compared to pure Bi_0.5Na_0.5TiO₃ ceramic, the partial substitutions of Y³⁺ for Bi³⁺ and Ba²⁺ for (Bi_0.5Na_0.5)²⁺ in the A-sites of Bi_0.5Na_0.5TiO₃ lower effectively the coercive field E _c and increase the remanent polarization P _r of the ceramics. Because of low E _c, large P _r and the MPB, the ceramics with x = 0–0.02 and y = 0.06 exhibit the optimum piezoelectric properties: d ₃₃ = 155–159 pC/N and k _p = 28.8–36.7%. The temperature dependences of dielectric properties of the ceramics show relaxor-like behaviors. The ferroelectric properties at different temperature suggest that the ceramics may contain both the polar and non-polar regions near/above T _d.     

Synthesis of Na0.5Bi0.5TiO3 anisotropic particles with grain orientation by conversion of Na0.5Bi4.5Ti4O15 crystals

Abstract

A novel method for synthesizing Na_0.5Bi_0.5TiO₃ (BNT) anisotropic particles with grain orientation is reported. Anisotropically shaped particles of BNT were prepared by conversion of Na_0.5Bi_4.5Ti₄O₁₅ (NBT15) single crystals. Platelet NBT15 was produced by molten-salt synthesis. They were converted to BNT by second molten-salt synthesis at 800—1200 ?C. NBT15 single-crystal platelets were transformed into platelet particles of polycrystalline BNT. The reaction is topotaxial, those recrystallized BNT were oriented with (h 0 0) plane parallel to the platelet. The use of converted BNT particles as seed was confirmed by performing templated grain growth (TGG) of BNT with 5% grain-oriented, anisotropic particles of BNT.