Spray-drying synthesis of P2-Na2/3Fe1/2Mn1/2O2 with improved electrochemical properties

Owing to its high theoretical capacity, P2-type Na_2/3Fe_1/2Mn_1/2O₂ has been considered as a kind of promising cathode material. However, the practical application is limited due to excessively high calcining temperature during traditional preparation processes. Here, we report the synthesis of P2-Na_2/3Fe_1/2Mn_1/2O₂ by using a facile spray-drying method followed by calcining at low temperature. Under the optimal conditions, the well-crystallized P2-Na_2/3Fe_1/2Mn_1/2O₂ material with excellent rate capability and cycle ability is obtained. And the sample exhibits the initial discharge capacities of 217.9, 171.3 and 117.4 mAh g⁻¹ at 0.1 C, 0.5 C and 2 C rate, respectively. The developed Na_2/3Fe_1/2Mn_1/2O₂ material, synthesized by a new spray drying-calcining procedure, may potentially be used as a suitable cathode in sodium ion batteries.     

Recovery of 1 2 5Sb from Neutron-Irradiated 1 2 4Sn

Recovery of ^{1 2 5}Sb from metallic tin (96% enrichment with ^{1 2 4}Sn) irradiated in a nuclear reactor (specific activity 5 mCi g^{- 1}) was studied. Irradiated tin was dissolved in concentrated HCl with addition of H₂O₂ or Br₂; dissolution was monitored with ^{1 1 9 m} Sn tracer. The separation of ^{1 2 5}Sb and tin was studied using strongly basic (Dowex-50, AV-17), moderately basic (AN-2FN), and weakly basic (AN-31) anion exchangers with HCl, HCl + HBr, and HNO₃ eluents. In the case of strongly basic anion exchangers, the separation coefficients of ^{1 2 5}Sb from tin reached 10⁴-10⁵ in a single cycle. From for AN-31 weakly basic anion exchanger, tin was almost completely removed with 0.8 M HCl; the yields of tin and ^{1 2 5}Sb were 99 and 98%, and the content of ^{1 2 5}Sb in tin was no more than 0.1% of the initial activity.     

Dielectric and piezoelectric properties of (0.97-x) Bi1/2Na1/2TiO3-xBi1/2K1/2TiO3-0.03NaNbO3 ceramics

Ceramics of the series (0.97-x)Bi_1/2Na_1/2TiO₃-xBi_1/2K_1/2TiO₃-0.03NaNbO₃ (x = 0, 0.02, 0.06, 0.10, 0.16, 0.20, 0.30) were prepared by the conventional mixed oxide method. Influence of Bi_1/2K_1/2TiO₃ content on the crystal structure, microstructure, dielectric and piezoelectric properties were studied. All compositions showed single perovskite phase and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase existed at the point of x = 0.16. Temperature dependences of permittivity and dissipation factor of unpoled samples revealed that permittivity increased with Bi_1/2K_1/2TiO₃ content and it reached maximum value near the MPB. At the same time, the peak value of dissipation factor increased with the addition of Bi_1/2K_1/2TiO₃. All the samples experienced two phase transitions: from ferroelectric to antiferroelectric at the first transition temperature (T_d) and from antiferroelectric to paraelectric at the temperature (T_m) corresponding to maximum value of permittivity. The phase transition from ferroelectric to antiferroelectric had relaxor characteristic and T_d shifted to lower temperature while increasing Bi_1/2K_1/2TiO₃ content. The best piezoelectric properties were obtained in 0.81Bi_1/2Na_1/2TiO₃-0.16Bi_1/2K_1/2TiO₃-0.03NaNbO₃ ceramic with a piezoelectric constant (d₃₃) of 146pC/N, planar electromechanical coupling factor (k_p) of 30.3% and thickness electromechanical coupling factor (k_t) of 53.2%. Abnormal piezoelectric properties were observed in the sample (x = 0.20), which was attributed to the co-existence of ferroelectric and antiferroelectric phases in it.     

The vapor pressure of 1, 1-dichloro-2, 2, 2-trifluoroethane (R123)

The vapor pressure of 1, 1-dichloro-2, 2, 2-trifluoroethane (R123) has been measured at temperatures between 256.4 and 453.8 K by ebulliometric and static techniques. These results have been combined to obtain a correlation for the vapor pressure from 256.4 K to the critical temperature.     

Phase-transition temperatures and piezoelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2Li1/2)TiO3-(Bi1/2K1/2)TiO3 lead-free ferroelectric ceramics.

The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a.     

Microstructure near 2 1 1 phase in high Jc MTG YBCO

The microstructures of MTG YBCO near 2 1 1 phase clusters inside the sample are studied by means of transmission electron microscopy. The results indicate that crystal defects around 2 1 1 phase are closely related to the distance between 2 1 1 particles (d _{2 1 1}). With the decrease ofd _{2 1 1}, the twin spacing increases. Simultaneously, the thickness of the twin boundary decreases. Whend _{2 1 1} is less than 0.51 m, there are almost no defects between 2 1 1 particles. According to the established crack model, the mechanism of the appearance of a defect-free-zone is explained. The relationship betweend _{2 1 1} and Jc is discussed in this paper.     

Electrical properties of Na1/2Nd1/2TiO3 Ceramics

The polycrystalline sample of Na_1/2Nd_1/2TiO₃ was prepared by a high-temperature solid-state reaction technique. The formation of the compound was confirmed by both XRD and EDX studies. Preliminary structural analysis ofNa_1/2Nd_1/2TiO₃ using X-ray diffraction data exhibits a tetragonal phase of the material at room temperature. The dielectric permittivity and the loss tangent of the pellet sample were obtained in a wide frequency range (1 kHz to 1 MHz) at different temperatures (30 °C to 425 °C). The dielectric anomaly at 114 °C, appearance of hysteresis loop and piezoelectric properties at room temperature confirmed the ferroelectric properties of the compound. Measurements of frequency and temperature dependence of impedance over a wide frequency range (100Hz–1MHz) were carried out by complex impedance spectroscopy as a non-destructive tool and indicate that the electrical properties of the material are strongly temperature dependent. Evidence of temperature dependence of electrical relaxation phenomenon as well as the negative temperature coefficient (NTC)-type of resistance behavior of the sample has also been observed. The dc conductivity graph follows the Arrhenius law. Studies of dielectric modulus suggest the non-Debye type of relaxation in the materials, which is supported by the impedance data.     

Efficient reverse converter design for the new four-moduli set {22n, 2n + 1, 2n/2 + 1, 2n/2 – 1}

Abstract

This paper presents a new four-moduli set {2²ⁿ, 2ⁿ + 1, 2^n/2 + 1, 2^n/2 – 1} (n even). According to new Chinese remainder theorem 1, an efficient algorithm is derived for converting four residue numbers to binary. Then, the converter architecture is designed using shorter bit-width carry propagate adders to improve the hardware performance considerably. Compared with existing converters for related four-moduli sets, the proposed converter shows higher speed and lower power consumption. The proposed converter design with 64-bit width has been implemented on the basis of the Taiwan Semiconductor Manufacturing Company 90-nm CMOS process. The chip area is 1622 × 1657 μm², and the working frequency is 116 MHz. The experimental results show that the proposed design achieves more than 26.9 and 18.4% savings in delay and power consumption, respectively. The converter also saves at least 39% in AD² (area × delay²).     

1D- and 2D-networks based on bis- and tris-(2-R-benzimidazol-1-yl)methanes

The supramolecular entities formed by five polybenzimidazolylmethanes,bis(2-tert-butylbenzimidazol-1-yl)methane 2, bis(2-(adamant-1-yl)benzimidazol-1-yl)methane 3, tris(2-ethylbenzimidazol-1-yl)methane 4, tris(2-isopropyl-benzimidazol-1-yl) methane 5, and tris(2-chlorobenzimidazol-1-yl)methane 6 have been investigated. Compounds 2 and 5 crystallize without any included guest, while compounds 3 (methanol and water), 4 (water), and 6 (cyclohexane) show their host properties.     

Distributions of Y2Ba1Cu1O5 particles in fluorine-doped Y1Ba2Cu3O x superconductors

An experimental study has been carried out on the relationship between Y₂Ba₁Cu₁O₅ particles in Y₁Ba₂Cu₃O _x superconductors and electric furnace cooling rates. As the electric furnace cooling rates decrease, the Y₂Ba₁Cu₁O₅ particles become uniformly disperse in fluorine-doped Y₁Ba₂Cu₃O _x superconductors. However, the Y₂Ba₁Cu₁O₅ particles do not appear in the undoped Y₁Ba₂Cu₃O_x superconductors.     

Lower Diffusion-Induced Stress in Nano-Crystallites of P2-Na2/3Ni1/3Mn1/2Ti1/6O2 Novel Cathode for High Energy Na-ion Batteries

P2-type Na_2/3Ni_1/3Mn_1/2Ti_1/6O₂ (NMTNO) cathode is a preeminent electrode material for Na-ion batteries owing to its open prismatic framework, air-moisture stability, inexpensiveness, appealing capacity, environmental benignity, and Co-free composition. However, the poor cycling stability, sluggish Na-ion kinetics induced in bulk-sized cathode particles, cracking, and exfoliation in the crystallites remain a setback. To outmaneuver these, a designing strategy of a mechanically robust, hexagonal nano-crystallites of P2-type Na_2/3Ni_1/3Mn_1/2Ti_1/6O₂ (NMTNO_nano) electrode via quick, energy-efficient, and low-cost microwave-irradiated synthesis is proposed. For the first time, employing a unified experimental and theoretical approach with fracture mechanics analysis, the mechanism behind the enhanced performance, better structural stability, and lower diffusion-induced stress of NMTNO_nano compared to micro-sized Na_2/3Ni_1/3Mn_1/2Ti_1/6O₂ is unveiled and the electrochemical shock map is predicted. The NMTNO_nano cathode provides 94.8% capacity retention after 100 cycles at 0.1 C with prolonged performance for 1000 cycles at 0.5 C. The practical viability of this cathode, tested in a full cell against a hard carbon anode delivered 85.48% capacity retention at 0.14 mA cm⁻² after 200 cycles. This work bridges the gap in correlating the microstructural and electrochemical properties through experimental, theoretical (DFT), and fracture mechanics analysis, thereby tailoring efficient cathode with lower diffusion-induced stress for high-energy Na-ion batteries.     

Structure transformations and dielectric properties of PbY1/2Nb1/2O3 and PbHo1/2Nb1/2O3 compounds

The metastable pseudomonoclinic perovskite phases, PbY_1/2Nb_1/2O₃ and PbHo_1/2Nb_1/2O₃ were prepared under conditions of high pressures and temperatures. Investigations of structural parameters, thermal stability and some dielectric properties were carried out. The data were analyzed by comparison with corresponding data of other representatives of the PbB_1/2³⁺Nb_1/2O₃ series. The dependence of unit cell parameters on the B³⁺ rare earth cation radius for the PbB_1/2³⁺Nb_1/2O₃ perovskites was correlated with a change of electronic structure of the rare earth elements, in particular, with the 4f-shell filling.     

Towards a frequency measurement of the Rydberg constant using the 2S-8S and 2S-8D transitions ofhydrogen

A very precise measurement of the Rydberg constant is performed using a direct-frequency comparison of the 2S-8S and 2 S-8D two-photon transitions in atomic hydrogen with the difference of two optical standards connected to a frequency chain     

Comparison of the Magnetic Ordering in Sr2Yb1Ru0.9Cu0.1O6 and Ru1Sr2Gd1Cu2O8 Superconductors

Ru₁Sr₂Gd₁Cu₂O₈ and Sr₂Yb₁Ru_0.9Cu_0.1O₆ were synthesized using a solid-state reaction. X-ray diffraction showed that Ru₁Sr₂Gd₁Cu₂O₈ crystallized into the tetragonal Ru-1212 structure (space group P4/mmm), whereas the Sr₂Yb₁Ru_0.9Cu_0.1O₆ had a monoclynic structure (space group P2₁/n). Sr₂Yb₁Ru_0.9Cu_0.1O₆ showed a possible magnetic transition ( T _{m a g} ) at 44 K with a superconducting transition temperature T _c at 30 K. In contrast, Ru₁Sr₂Gd₁Cu₂O₈ showed a magnetic transition at 140 K with a T _c at 25 K. The magnetization data for Sr₂Yb₁Ru_0.9Cu_0.1O₆ suggests that this sample exhibits antiferromagnetic ordering in zero-field-cooled (ZFC) magnetization, whereas it reveals a weak ferromagnetic component during field-cooled (FC) cycles. In addition, larger diamagnetic signals were observed during FC cycle compared to the ZFC. These results suggest that the valence state of the Yb ion have a significant effect on the magnetic state of the Sr₂Yb₁Ru_0.9Cu_0.1O₆ superconductor.     

Microwave characteristics of Sm(Co1/2Ti1/2)O3 dielectric resonators

The microwave dielectric properties of Sm(Co_1/2Ti_1/2)O₃ ceramics have been investigated. Sm(Co_1/2Ti_1/2)O₃ ceramics were prepared by conventional solid-state route. The dielectric constant values (ε_r) saturated at 23.5–25.5. The Q×f values of 21,500–76,000 (at 10 GHz) can be obtained when the sintering temperatures are in the range of 1300–1420 °C. The temperature coefficient of resonant frequency τ_f was a function of sintering temperature. The ε_r value of 25.5, Q×f value of 76,000 (at 10 GHz) and τ_f value of −16.3 ppm/°C were obtained for Sm(Co_1/2Ti_1/2)O₃ ceramics sintered at 1360 °C for 4 h. For applications of high selective microwave ceramic resonator, filter and antenna, Sm(Co_1/2Ti_1/2)O₃ is proposed as a suitable material candidate.     

Scalable and controllable synthesis of 2D high-proportion 1T-phase MoS2

Two-dimensional molybdenum disulfide (2D MoS₂) is considered as a promising candidate for many applications due to its unique structure and properties. However, the controllable synthesis of large-scale and high-quality 2D 1T-phase MoS₂ is still a challenge. Herein, we present the scalable and controllable synthesis of 2D MoS₂ from 2H to 1T@2H phase by using K₂SO₄ salt as a simultaneous high-temperature sulfur source and template. The as-synthesized 1T@2H-2D MoS₂ exhibits a high yield and can be easily assembled into freestanding electrode with high specific capacitance of 434 F/g at a scan rate of 1 mV/s in LiClO₄ ethylene carbonate/dimethyl carbonate (EC/DMC). Moreover, various single-crystal 2D transition metal sulfides (WS₂, PbS, MnS and Ni₉S₈) and 2D S-doped carbon can be synthesized using this method. We believe that this study may provide a new sight for scalable and controllable synthesis of other 2D materials beyond 2D MoS₂.

     

The magnetodielectric effect in Bi1/2La1/2MnO3 cramics

We present measurement results of the magnetodielectric effect in Bi_1/2La_1/2MnO₃ ceramics at temperature T = 80 K in a wide frequency range. It is revealed that an increase in the magnetic induction leads to a monotonous increase in the real part of the dielectric permittivity or to a monotonous decrease/increase in the imaginary part, depending on the frequency of the measuring electric field. The origin of the magnetodielectric effect is discussed.     

Microstructures and Tensile Properties of Isothermally-forgedTi-47Al-2Nb-1Cr-1V and Ti-47Al-2V-1Cr Alloys

Microstructures and room-temperature tensile properties of isothermally-forged γ-base (γ + α2)alloys in Ti-Al-Nb-Cr-V system with different heat treatments were investigated. The results show that the microstructures of Ti-47Al-2Nb-1Cr-1V and Ti-47Al-2V-1Cr (at. pct) alloys are mainly determined by heat treating temperature in the (cr + 7) tWo-phase field, and the joint additions of Nb, Cr and V in the Ti-47Al alloy afFect Ta significantIy. The microstructure of Ti-47Al alloy with additions of Nb, Cr and V (1~2 at. pct) can be dupIex or nearly-lamellar by a suitable heat treatment after isothermal forging at 1000℃ for over 50% plastic strains.Therefore its tensile properties can be improved at room temperature.     

Photocatalytic H2 Evolution on TiO2 Assembled with Ti3C2 MXene and Metallic 1T-WS2 as Co-catalysts

The biggest challenging issue in photocatalysis is efficient separation of the photoinduced carriers and the aggregation of photoexcited electrons on photocatalyst’s surface.In this paper,we report that double metallic co-catalysts Ti3C2 MXene and metallic octahedral(1T)phase tungsten disulfide(WS2)act pathways transferring photoexcited electrons in assisting the photocatalytic H2 evolution.TiO2 nanosheets were in situ grown on highly conductive Ti3C2 MXenes and 1T-WS2 nanoparticles were then uniformly distributed on TiO2@Ti3C2 composite.Thus,a distinctive 1T-WS2@TiO2@Ti3C2 composite with double metallic co-catalysts was achieved,and the content of 1T phase reaches 73%.The photocatalytic H2 evolution performance of 1T-WS2@TiO2@Ti3C2 composite with an optimized 15 wt%WS2 ratio is nearly 50 times higher than that of TiO2 nanosheets because of conductive Ti3C2 MXene and 1T-WS2 resulting in the increase of electron transfer efficiency.Besides,the 1T-WS2 on the surface of TiO2@Ti3C2 composite enhances the Brunauer–Emmett–Teller surface area and boosts the density of active site.     

Microwave-induced combustion synthesis and electrical conductivity of Ce1−xGdxO2−1/2x ceramics

Ce_1−xGd_xO_2−1/2x nanopowder were successfully synthesized by microwave-induced combustion process. For the preparation, cerium nitrate, gadolinium nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only 30 min to obtain Ce_1−xGd_xO_2−1/2x powders. The exo-endo temperature, phase identification, and morphology of resultant powders were investigated by TG/DTA, XRD, and SEM. The as-received Ce_1−xGd_xO_2−1/2x powders showed that the average particle size ranged from 18 to 50 nm, crystallite dimension varied from 11 to 20 nm, and the specific surface area was distribution from 16 to 46 m²/g. As for Ce_1−xGd_xO_2−1/2x ceramics sintered at 1450 °C for 3 h, the bulk density of Ce_1−xGd_xO_2−1/2x ceramics were over 91% of the theoretical density, the maximum electrical conductivity, σ_700 °C = 0.017 S/cm with minimum activation energy, E_a = 0.869 eV was found at Ce_0.80Gd_0.20O_1.90 ceramic.