High energy-storage properties of Bi0.5Na0.5TiO3-BaTiO3-SrTi0.875Nb0.1O3 lead-free relaxor ferroelectrics

New lead-free ferroelectric (0.94-x)Bi_0.5Na_0.5TiO₃-0.06BaTiO₃-xSrTi_0.875Nb_0.1O₃ (BNBT-STN, x = 0 and 0.2) are synthesized by using a solid state reaction process. In this work, an obvious evolution of dielectric relaxation behavior and slim P–E hysteresis loops with high P_max and low P_r is observed for BNBT-0.2STN, indicating the dominant of ergodic relaxor phase with dynamic polar nano-regions (PNRs). A relatively large recoverable energy density (W_rec = 1.17 J/cm³) with high energy efficiency (η = 91%) is obtained. Furthermore, it shows small variation (9%) in the temperature range of 30–150 °C and fatigue-free behavior, which can be attributed to the absence of ferroelectric domain in the relaxor phase. The achievement of these characteristics provides that tailoring by B-site vacancies is a potential route when designing a new energy-storage system for BNT-based relaxor ferroelectric materials.     

Influence of SrTiO3 modification on dielectric properties of Mg(Zr0.05Ti0.95)O3 ceramics at microwave frequency

The microwave dielectric properties and microstructures were investigated in the (1?x)Mg(Zr_0.05Ti_0.95)O₃–xSrTiO₃ (hereafter referred to as (1?x)MZT–xST) system. The compounds were prepared via the conventional solid-state reaction. Compositions in the (1?x)Mg(Zr_0.05Ti_0.95)O₃–xSrTiO₃ system were designed to compensate the negative temperature coefficient of the resonant frequency of Mg(Zr_0.05Ti_0.95)O₃. The values displayed nonmonotonic mixture-like behavior, because the TiO₂ phase was formed in the MZT composite ceramics with increasing x. A close zero τ_f of 0.2 ppm/°C could be achieved at 0.96MZT–0.04ST with ?_r = 20.8 and Q × f = 257,000 GHz.     

Core-shell structured MoS2@S spherical cathode with improved electrochemical performance for lithium-sulfur batteries

To suppress shuttling effect and improve electrochemical performance of the sulfur cathode for lithium-sulfur batteries, core-shell structured MoS₂@S spherical cathode has been synthesized through a chemical route using MnCO₃ as template. The MoS₂ shells consist of MoS₂ nanosheets. For comparison, MoS₂/S cathode has also been synthesized through melting and diffusion of sulfur to commercial MoS₂ powders. The electrochemical performance of the MoS₂@S and MoS₂/S cathodes have been evaluated using cyclic voltammetry, discharge/charge cycling, electrochemical impedance spectroscopy coupled with impedance fitting. The electrochemical performance of the MoS₂@S spherical cathode has been much improved compared with that of MoS₂/S. The capacity of the MoS₂@S spheres can reach 1185.7 mA h g^?1 at 0.2 C and 955.1 mA h g^?1 at 1 C with initial-cycle coulombic efficiency of 90%. The capacity fading of each cycle is 0.1% during 200 lithiation/delithiation cycles. The MoS₂@S spherical cathode with high cyclic capacity and stability is promising cathode candidate for lithium-sulfur batteries.     

High efficiency visible-light-driven Fe2O3-xSx/S-doped g-C3N4 heterojunction photocatalysts: Direct Z-scheme mechanism

Several nanoporous Fe_2 O_3-xSx/S-doped g-C_3 N_4(CNS) Z-scheme hybrid heterojuctions have been successfully synthesized by one-pot in situ growth of the Fe_2O_3-xSx particles on the surface of CNS. The characterization results show that S-doping in the g-C3 N4 backbone can greatly enhance the charge mobility and visible light harvesting capability. In addition, porous morphology of hybrid composite provides available open pores for guest molecules and also improves light absorbing property due to existence of multiple scattering effects. More importantly, the Fe_2 O_3-xSx nanoparticles formed intimate heterojunction with CNS and developed the efficient charge transfer by extending interfacial interactions occurred at the interfaces of both components. It has been found that the Fe_2 O_3-xSx/CNS composites have an enhanced photocatalytic activity under visible light irradiation compared with isolated Fe_2 O_3 and CNS components toward the photocatalytic degradation of methylene blue(MB). The optimal loaded Fe_2 O_3-xSx value obtained is equal to 6.6 wt% that provided 82% MB photodegradation after 150 min with a reaction rate constant of 0.0092 min~(-1) which was faster than those of the pure Fe_2 O_3(0.0016 min~(-1))and CNS(0.0044 min~(-1)) under the optimized operating variables acquired by the response surface methodology. The specific surface area and the pore volume of Fe_2 O_3(6.6)/CNS hybrid are 33.5 m~2/g and0.195 cm~3/g, which are nearly 3.8 and 7.5 times greater compared with those of the CNS, respectively. The TEM image of Fe_2 O_3(6.6)/CNS nanocomposite exhibits a nanoporous morphology with abundant uniform pore sizes of around 25 nm. Using the Mott-Schottky plot, the conduction and valence bands of the CNS are measured(at pH = 7) equal to-1.07 and 1.48 V versus normal hydrogen electrode(NHE), respectively.Trapping tests prove that ·OH-and ·O_2-radicals are major active species in the photocatalytic reaction.It has been established that formation of the Z-scheme Fe_2 O_3(6.6)/CNS heterojunction between CNS and Fe_2 O_3 directly produces ·OH as well as ·O_2-radicals which is consistent with the results obtained from trapping experiments.     

Electrochemical properties of (La1−xTix)0.67Mg0.33Ni2.75Co0.25 (x = 0-0.20, at%) hydrogen storage alloys

(La_1−xTi_x)_0.67Mg_0.33Ni_2.75Co_0.25 (x = 0, 0.05, 0.10, 0.15 and 0.20, at%) alloys are synthesized by arc-melting and subsequent heat solid-liquid diffusing techniques, and the crystalline structures and electrochemical properties of the alloys are investigated systematically. The structural analysis results show that all the alloys mainly consist of (La, Mg)Ni₃ phase with the rhombohedral PuNi₃-type structure and LaNi₅ phase with the hexagonal CaCu₅-type structure. However, when the Ti content is higher than 0.10, a little amount of TiNi₃ phase start to form. Electrochemical measurements show that the alloy electrodes could be activated to their maximum discharge capacity within four cycles, the maximum discharge capacity is around 321.9-384.6 mAh g⁻¹, both the cyclic stability and the high-rate discharge ability first increased and then decrease with increasing x. All the results show that a little amount of Ti substitution for La in AB₃-type hydrogen storage alloys is effective to the improvement of the overall electrochemical properties.     

Pseudo-quinary Ti20Zr20Hf20Be20(Cu20 -xNix) high entropy bulk metallic glasses with large glass forming ability

A series of pseudo-quinary Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu_20 -xNi_x) (x = 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20 at.%) high entropy bulk metallic glasses (HE-BMGs) with large glass forming ability (GFA) were successfully prepared by copper mold tilt-casing. The critical diameters (D_c) of these HE-BMGs are all above 12 mm. In particular, the developed Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu_7.5Ni_12.5) and Ti₂₀Zr₂₀Hf₂₀Be₂₀Ni₂₀ high entropy alloys (HEAs) can be produced in the amorphous state with diameters up to 30 mm and 15 mm, respectively, which are the largest HE-BMG and quinary HE-BMG hitherto. The two HE-BMGs also exhibit high yield strength, together with the plastic strain values of (3.0 ± 1.1) % and (4.0 ± 0.9) %, respectively. With increasing Ni additions in the pseudo-quinary HEAs, the crystallization growth resistance and thermal stability have been improved, which is apparently due to the sluggish diffusion of the atoms in the HEAs.     

Microstructure and brazing mechanism of porous Si3N4/Invar joint brazed with Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler

Porous Si_3N_4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe_2Ti and Ni_3Ti intermetallic compounds. The effects of the brazing temperature and the thickness of Cu interlayer on the microstructure and mechanical properties of brazed joints were investigated. The typical microstructure of the joint brazed with multi-layered filler was porous Si_3N_4/TiN + Ti_5Si_3/Ag-Cu eutectic/Cu/Ag-Cu eutectic/Cu-rich layer + diffusion layer/Invar. When the brazing temperature increased, the reaction layer at the ceramic/filler interface grew thicker and the Cu interlayer turned thinner. As the thickness of Cu interlayer increased from 50 to 150μm, the joint strength first increased and then decreased. In this research, the maximum shear strength(73 MPa) was obtained when being brazed at 1173 K with a 100μm Cu interlayer applied in the filler, which was 55% higher than that brazed with single Ag-Cu-Ti brazing alloy and had reached 86% of the ceramic. The release of residual stress and the barrier effect of Cu interlayer to inhibit the formation of Fe_2Ti and Ni_3Ti intermetallics played the major role in the improvement of joint strength.     

Ferromagnetic element microalloying and clustering effects in high Bs Fe-based amorphous alloys

Fe_(83)(Co_x,Ni_y)(B_(11)Si_2P_3C_1)_(1-x,y/17)(x,y=1–3)amorphous alloys with high saturation magnetic flux density(B_s)and excellent soft-magnetic properties were developed and then the microalloying and clustering effects were explored.The microalloying of Co and Ni improves the B_sfrom 1.65 T to 1.67–1.72 T and 1.66–1.68 T,respectively.The Ni-doped alloys exhibit better soft-magnetic properties,containing a low coercivity(H_c) of about 5.0 A/m and a high Effective permeability(μ_e)of(8–10)×10~3,whereas the microalloying of Co leads to a deteriorative H_c of 5.0–13.0 A/m and a μ_eof(5–8)×10~3.Moreover,microalloying of Ni can increase the ductile-brittle transition(DBT)temperature of the ribbons,while a totally opposite effect is found in the Co-doped alloys.The formation of dense α-Fe(Co,Ni)clusters during annealing process is used to explain the distinct effects of Co and Ni microalloying on the magnetic properties and bending toughness.     

Synthesis and photoluminescence of Ca1-xTiO3:xEu3+ nanoparticles

Ca_1-xTiO₃:xEu³⁺ nanoparticles (NPs) with the size ranging from 27 nm to 135 nm were prepared by means of a chemical co-precipitation method. The structural and optical properties of the NPs were investigated, and the influence of Eu doping content and sintering temperature on the photoluminescence of the Ca_1-xTiO₃:xEu³⁺ NPs were examined. An obvious red emission band centered at 615 nm were observed under the excitation with 395 nm for the Ca_1-xTiO₃:xEu³⁺ NPs. X-ray photoelectron spectroscopy analyses suggest that Eu³⁺ is incorporated into not only the Ca-site, but also Ti-site of CaTiO₃ crystal lattice. Our study shows the promise of the Ca_1-xTiO₃:xEu³⁺ NPs as a red nanophosphor.     

Structures and electrochemical performances of as-spun RE-Mg-Ni-Co-Al alloys applied to Ni-MH battery

The La-Mg-Ni-Co-Al-based AB₂-type La_0.8-xCe_0.2Y_xMgNi_3.4Co_0.4Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) alloys were prepared by melt spinning. The effects of Y content on the structures and electrochemical hydrogen storage characters were thoroughly studied. The structures of the experimental samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is shown that there are a main phase LaMgNi₄ and a second phase LaNi₅ in the experimental samples. The variation of Y content incurs obvious changes of the phase abundance without changing phase composition. Namely, with the increase of Y content, the LaMgNi₄ phase increases and LaNi₅ phase decreases. Furthermore, melt spinning and the replacement of Y for La also lead to the grains refinement of the alloy. The electrochemical tests display that the as-spun alloys possess excellent activation properties, and obtain the maximums of discharge capacity at the first cycling. The replacement of Y for La can visibly facilitate the discharge potential characteristics, however,diminish the discharge capacity. The electrochemical kinetics, involving in the high rate discharge ability (HRD), hydrogen diffusion coefficient (D), limiting current density (I_L) and charge transfer rate, increases firstly and then decreases with the increase of Y content. The cyclic stability is greatly improved by melt spinning and the replacement of Y for La, which is derived from the improvement of the anti-corrosion, oxidation-resistance and the anti-pulverization abilities.     

Brazing of SiO2f/SiO2 composite modified with few-layer graphene and Invar using AgCuTi alloy

Due to the poor wettability of the AgCuTi alloy on the SiO_2f/SiO₂ composite, direct brazing of the composite with an Invar alloy could hardly achieve a reliable joint. To overcome that, the SiO_2f/SiO₂ composite was decorated with few-layer graphene (FLG) by a plasma enhanced chemical vapor deposition (PECVD) method. Sessile drop experiments indicate that the contact angle dropped from 123.8° to 50.7° after FLG was grown on the surface of the SiO_2f/SiO₂ composite. Afterwards, the effects of brazing temperature and Ti contents on the microstructure evolution and mechanical properties of joints (Invar/SiO_2f–SiO₂ modified with FLG) were investigated. The typical interface structure of the joint is SiO_2f–SiO₂/Ti₅Si₃ + TiO₂ + Cu_xTi_6 − xO(x = 2,3)/Ag(s,s) + Cu(s,s) + Cu–Ti blocks/wave-like Fe₂Ti + Ni₃Ti/Ag(s,s) + Cu(s,s) + Fe₂Ti + Ni₃Ti blocks/Invar. As the brazing temperature and Ti contents increase, the reaction layer on the SiO_2f/SiO₂ side becomes thicker and cracks gradually propagate. Meanwhile, a few dispersive Fe₂Ti + Ni₃Ti phases change into large-area wave-like compounds and more Cu–Ti compounds form with the increase of the Ti content. The microstructure evolution significantly affects the shear strength of the brazed joints. The highest shear strength is 26 MPa brazed at 860 °C for 10 min with 4.5 wt.% Ti content.     

Synthesis of three-dimensionally ordered porous perovskite type LaMnO3 for Al-air battery

LaMnO₃ catalysts with three-dimensionally ordered holes perovskite structure were prepared via close-packed SiO₂ template synthesized by Stöber-Frink method. SEM, XRD and BET were employed to characterize the microstructure, phases and specific surface area. CV method was used to the oxygen electrode behavior of catalysts. Diameter of the holes was about 330 nm, corresponding to the size of SiO₂ template. Full-cell discharge tests were performed on aluminum-air battery fabricated by porous LaMnO_3. Results showed that the discharge performance of porous LaMnO₃ were 1.54 V, 1.42 V and 1.24 V respectively when the discharge currents were set at 5 mA/cm², 10 mA/cm² and 20 mA/cm², respectively, which were higher than that of LaMnO₃ prepared by coprecipitation method (1.33 V, 1.09 V, 0.63 V, respectively).     

Structural and electrochemical characterization of layered 0.3Li2MnO3·0.7LiMn0.35−x/3Ni0.5−x/3Co0.15−x/3CrxO2 cathode synthesized by spray drying

Cr doped 0.3Li₂MnO₃·0.7LiMn_0.35−x/3Ni_0.5−x/3Co_0.15−x/3Cr_xO₂ (x = 0, 0.02, 0.04, 0.06) as a cathode material for Li-ion battery has been successfully synthesized by spray drying and subsequent calcination. The effects of Cr dopant on the structural and electrochemical properties of this material have been investigated by XRD, SEM, EDS, charge–discharge measurements, Ac impedance spectroscopy as well as cyclic voltammetry. These results demonstrated that the element Cr distributed uniformly in these materials. With the Cr content increasing, lattice parameters a and c decrease and less Li ion locates in transition metal site. Among the synthesized Cr-doped materials, when x = 0.04, this material shows the best electrochemical properties. Between 2.5 and 4.8 V (vs. Li/Li⁺), the initial discharge capacities of the materials increased from 143 to 168 mA h g⁻¹ at a constant current density of 250 mA g⁻¹. After 50 cycles, the capacity retention of the materials raised from 83% to 93%.     

Synthesis and electrochemical performance of Li1+xNi0.5Mn0.3Co0.2O2+δ (0 ≤ x ≤ 0.15) cathode materials for lithium-ion batteries

In this work, layered lithium-excess materials Li_1+xNi_0.5Mn_0.3Co_0.2O_2+δ (x = 0, 0.05, 0.10 and 0.15), of spherical morphology with primary nanoparticles assembled in secondary microspheres, were synthesized by a coprecipitation method. The effects of lithium content on the structure and electrochemical performance of these materials were evaluated by employing X-ray diffraction (XRD), inductive coupled plasma (ICP), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge tests. It is found that Li_1.10Ni_0.5Mn_0.3Co_0.2O_2+δ, i.e., Li[(Ni_0.5Mn_0.3Co_0.2)_0.95Li_0.05]O₂ showed the best electrochemical performance due to the highly ordered layered structure, reduced cation mixing and the lowest charge transfer resistance. Li_1.10Ni_0.5Mn_0.3Co_0.2O_2+δ delivered a discharge capacity of 145 mA h g^?1 at 125 mA g^?1 in the cut-off voltage of 2.5–4.3 V, and had a capacity retention of 100% after 50 cycles at room temperature.     

A comparison study of hydrogen storage properties of as-milled Sm5Mg41 alloy catalyzed by CoS2 and MoS2 nano-particles

The influences of the catalysts of CoS₂ and MoS₂ nano-particles on microstructure and hydrogen storage behaviors of as-milled Sm₅Mg₄₁ alloy have been compared in this work. The Sm₅Mg₄₁ + 5 wt.% M (M = CoS₂, MoS₂) alloys were prepared by milling the mechanical ground as-cast Sm₅Mg₄₁ alloy powders (particle size ≤ 75 μm) with 5 wt.% CoS₂ or MoS₂ nano-particles (particle size ≤ 30 nm), respectively. The results demonstrate that the CoS₂ and MoS₂ nanoparticles are embedded into the alloy surface, which is nanostructure containing some crystal defects, such as dislocation, grain boundary and twin etc. Those microstructures play a beneficial role in reducing the total potential barrier that the hydrogen absorption or desorption reactions must overcome, hence improving the hydrogen storage kinetics of the alloys. The as-milled alloys are composed of Sm₅Mg₄₁ and SmMg₃ phases, and ball milling refines their crystal grains. The MgH₂ and Sm₃H₇ phases appear after hydrogenation, while Mg and Sm₃H₇ phases exist after dehydrogenation. The dehydriding activation energy of M = CoS₂ and MoS₂ alloys are 101.67 and 68.25 kJ/mol H₂ respectively. The initial hydrogen desorption of M = CoS₂ and MoS₂ alloys are 252.9 °C and 247.8 °C. The hydrogenation and dehydrogenation enthalpy changes of M = MoS₂ alloy are a little smaller than that of M = CoS₂ alloy. Therefore, the catalyst MoS₂ can improve the as-milled Sm₅Mg₄₁ alloy in hydrogen storage property more effectively than CoS₂.     

Formation and thermal properties of fluorite-pyrochlore composite structure in La2(ZrxCe1 − x)2O7 oxide system

Rare-earth oxides of La₂(Zr_xCe_1 ? x)₂O₇ for thermal barrier coatings (TBCs) are fabricated via a solid-state reaction at 1600 °C. As the phase formation, microstructure, and thermal properties of these oxides are examined, a fluorite–pyrochlore composite structure is found in the La₂(Zr_xCe_1 ? x)₂O₇ system. This composite structure is composed of coarse Ce-rich fluorite and fine Zr-rich pyrochlore grains. From XRD and microstructural analysis, the lattice parameter and volume fraction of each phase are evaluated in order to obtain the intrinsic thermal conductivity value of composite-structured oxide with porosity calibration. The thermal conductivity of the composite structure is similar to that of pyrochlore La₂Zr₂O₇, which is attributed to phonon scattering by phase boundaries.     

Microstructural study of a titanium-based biocomposite produced by the powder metallurgy process with TiH2 and nanometric β-TCP powders

A titanium-based composite with Ca-P phases was prepared in situ by powder metallurgy processing with TiH₂ and nanometric β-TCP powders. Crystal phases of the as-fabricated composite are found to be α-Ti, CaTiO₃ and Ti_xP_y phase(s). The Ti_xP_y and CaTiO₃ phases resulted from the reaction between titanium and β-TCP at about 1135 °C. The composite presented a mean compressive strength of 635 MPa and a lower contact angle than pure titanium.     

Effect of rapid quenching on the microstructures and electrochemical characteristics of La0.7Mg0.3Ni2.55−xCo0.45Alx (x = 0–0.4) electrode alloys

A new type of hydrogen storage alloy La_0.7Mg_0.3Ni_2.55−xCo_0.45Al_x (x = 0, 0.1, 0.2, 0.3, 0.4) with a PuNi₃-type structure (R− 3m) were prepared by casting and rapid quenching. The effects of the rapid quenching on the microstructures and electrochemical performances of the specimen alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure, including the (La, Mg)Ni₃ phase, the LaNi₅ phase and the LaNi₂ phase. The rapid quenching had an inappreciable influence on the phase composition of the alloys, but it obviously changed the phase abundance of the alloys. The rapid quenching can significantly improve the compositional homogeneity and markedly decrease the grain size of the alloys. The results obtained by the electrochemical measurements indicate that the rapid quenching obviously enhanced the cyclic stability of the alloys, but it decreased the discharge capacity and activation capability of the alloys.     

Hydrolytic dehydrogenation of ammonia borane catalyzed by poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets supported Ag0.3Co0.7 nanoparticles

Poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets (PAMAM/rGO) composite was selected as a carrier of heterogeneous Ag_0.3Co_0.7 nanoparticles in order to obtain an excellent catalyst for ammonia borane (AB) hydrolysis. During the synthetic processes, GO could easily assembled with PAMAM by the electrostatic and hydrogen-bonding interactions. Structural characterization revealed that Ag_0.3Co_0.7 bimetallic nanoparticles with uniform size distribution of 5 nm are well dispersed on PAMAM/rGO composite architecture. Ag_0.3Co_0.7@PAMAM/rGO was found to be a highly active and reusable catalyst in hydrogen generation from the hydrolysis of AB with a turnover frequency value (TOF) of 19.79 mol_H2 min^–1 mol_M^–1 at 25.0 ± 0.1 °C and retained 75.4% of their initial activity with a complete release of hydrogen in five runs. The relatively high TOF value and low apparent activation energy (34.21 kJ mol^–1) make these Ag_0.3Co_0.7@PAMAM/rGO NPs as a high-efficient catalyst for catalytic dehydrogenation of AB facilitating the development of practically applicable energy storage materials.     

A new scale for optimized cryogenic magnetocaloric effect in ErAl2@Al2O3 nanocapsules

The Er Al_2@Al_2O_3nanocapsules with Er Al_2core and Al_2O_3shell were synthesized by modified arc-charge technique.The typical core-shell structure of the nanocapsules was confirmed by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy.Transmission electron microscopy analysis shows the irregular sphere of the nanocapules with an average diameter of 26 nm.Magnetic investigation revealed the Curie temperature of Er Al_2@Al_2O_3nanocapsules at 20 K and the typical superparamagnetic behavior between blocking temperature and Curie temperature.Based on the blocking temperature and average diameter,the magnetocrystalline anisotropy constant of Er Al_2@Al_2O_3nanocapsules was estimated to illustrate the magnetic contribution to the-S_M.The large-S_Mof 14.25 J/(kg K)was obtained under 50 k Oe at 5 K.A vital parameterˇwas introduced in the present work to scale the optimized magnetic characteristics and the optimized mechanism was discussed in detail according to classical superparamagnetic theory.The results demonstrate that the optimal-S_Mwill be obtained when the magnetic parameterˇis close to the theoretical coefficient.