Disodium tricopper(II) tetra­kis[selenate(IV)] tetra­hydrate

The title compound, Na2Cu3(SeO3)4(H2O)4, has been prepared under hydro­thermal conditions. The crystal structure contains a three-dimensional anionic framework made up from distorted [CuO4(H2O)2] octa­hedra ( symmetry), [CuO4(H2O)] square pyramids and trigonal-pyramidal SeO3 units sharing common corners. The connectivity among these units leads to four- and eight-membered polyhedral rings, which by edge-sharing inter­connect into walls. A rhombus-like 16-membered polyhedral ring channel system with a longest length of approximately 14.0 Å and a shortest length of 5.3 Å is enclosed by such walls along the a axis. The water mol­ecules attached to the Cu atoms, as well as the electron lone pairs of the SeIV atoms, protrude into these channels. The seven-coordinated Na+ counter-cations occupy the remaining free space of the 16-membered polyhedral ring channels. An intricate network of O—H⋯O hydrogen bonds further consolidates the three-dimensional structure

Syntheses and characterizations of rare earth compounds RE(HCO2)(3)(HNO2) (H2CO2) (RE = Y, Tb, Dy, Ho, Er, Yb, Tm)

A series of novel inclusion compounds with compositions of RE(HCO2)(3)(HNO2)( H2CO2) (RE = Y, Tb, Dy, Ho, Er, Yb, Tm) were synthesized and structures were characterized by X-ray methods. The orthorhombic structure was shown to be a new type with a non-centrosymmetric space group (20) C222(1) by single crystal structure determinations. It is characterized by networks of rare earth centered square anti-prisms formed by eight oxygen atoms through bridging carbon and nitrogen atoms. The guest formic acid molecules H2CO2 are distributed inside the open tunnels along the crystallographic a axis. The magnetic susceptibility measurements show the heavy rare earth compounds follow the Curie-Weiss law and the calculated numbers of Bohr magnetons are consistent with the RE3+ ions. The yttrium compound shows very weak temperature independent paramagnetism

Photoluminescence properties of Eu2+-activated Ca2Y2Si2O9 phosphor

Eu2+-activated Ca2Y2Si2O9 phosphors with different Eu2+ concentrations have been prepared by a solid-state reaction method at high temperature and their photoluminescence (PL) properties were investigated. Photoluminescence results show that Eu2+-doped Ca2Y2Si2O9 can be efficiently excited by UV–visible light from 300 to 425 nm. Ca2Y2Si2O9: Eu2+ exhibits broad band emission in the wavelength range of 425–700 nm, due to the 4f65d1 ¿ 4f75d0 transition of the Eu2+ ions located at two different sites ((Ca/Y)1 and (Ca/Y)2) in Ca2Y2Si2O9. The effect of the Eu2+ concentration in Ca2Y2Si2O9 on the PL properties was investigated in detail. The results showed that the relative PL intensity reaches a maximum at 1 mol% of Eu2+, and a red-shift of the emission bands from these two different sites was observed with increasing Eu2+ concentration. Also there exists energy transfer between these two Eu2+ sites. The potential applications of Ca2Y2Si2O9: Eu2+ have been pointed out

Aerodynamic analysis of insect-like flapping wings in fan-sweep and parallel motions with the slit effect

In this study, the aerodynamic performance of flapping wings using a parallel motion was investigated and compared with the insect-like “fan-sweep” motion, and the effect of adding a slit to the wings was analyzed. First, numerical simulations were performed to analyze the wing aerodynamics of two flapping motions with equivalent stroke amplitudes over a range of pitching angles based on computational fluid dynamics (CFD). The simulation results indicated that flapping wings with a rapid and short parallel motion achieved better lift and efficiency than those of the fan-sweep motion while maintaining the same aerodynamic characteristics regarding stall delay and leading-edge vortices. For a parallel motion with a pitching angle of 25° and 100 mm stroke amplitude, the wings generated an average lift of 8.4 gf with a lift-to-drag ratio of 1.06, respectively, which were 1.8% and 26% greater than those of the fan-sweep motion with a corresponding 96° stroke amplitude. This situation was reversed when the pitching angle and stroke amplitude were increased to 45° and 144° for the fan-sweep motion, which was equivalent to the parallel motion with a 150 mm stroke amplitude. The slit effect in the parallel motion was also evaluated, and the CFD results indicated that a slit width of 1 mm (1/50 wing chord) increased the lift of the wing by approximately 27% in the case of the 150 mm stroke amplitude. Further, the slit width slightly influenced the lift and aerodynamic efficiency

Intentional Carrier Doping to Realize n-Type Conduction in Zintl Phases Eu5−yLayIn2.2Sb6

Due to the tunable electrical transport properties and lower thermal conductivity, Zintl phase compounds have been considered as a promising candidate for thermoelectric applications. Most Sb-based Zintl compounds exhibit essentially p-type conduction as result of the cation vacancy. Herein, n-type Zintl phases Eu5−yLayIn2.2Sb6 has been successfully synthesized via controlling the vacancy defect combined with intentional electron doping. Excess of In would occupy the vacancy while La doping enables the electron to be the major carrier at the measured temperate range, realizing the n-type conduction for Eu5−yLayIn2.2Sb6 (y ≥ 0.04). Meanwhile, the thermal conductivity of Eu5−yLayIn2.2Sb6 reduces from 0.90 W/mK to 0.72 W/mK at 583 K derived from the La doping-induced disorder. The maximum thermoelectric figure of merit zT = 0.13 was obtained. This work firstly realizes the n-type conduction in Eu5In2Sb6, which sheds light on the strategy to synthesize n-type Zintl thermoelectric materials and promotes the practical applications of Zintl thermoelectric devices

Preparation, characterization, and photoluminescence properties of Tb 3+-, Ce3+-, and Ce3+/Tb3+-activated RE2Si4N6C (RE = Lu, Y, and Gd) phosphors

Photoluminescence properties of Tb3+ and Ce3+ singly doped and Ce3+/Tb3+-codoped RE2Si 4N6C (RE = Lu, Y, and Gd) phosphors were investigated. Tb3+ shows similar luminescence properties in RE2Si 4N6C (RE = Lu, Y, and Gd) host lattices and emits bright green light under UV excitation around 300 nm. The luminescence properties of Ce3+ in RE2Si4N6C host lattices are influenced by the size of the RE3+ ions (Lu2Si 4N6C and Y2Si4N6C vs Gd2Si4N6C). Both Ce3+-activated Lu2Si4N6C and Y2Si4N 6C phosphors exhibit a broad band emission in the wavelength range of 450-750 nm with peak center at about 540 nm, while Ce3+-activated Gd2Si4N6C shows a broad emission band in the wavelength range of 500-800 nm with peak center at about 610 nm. This difference is ascribed to the different site occupations of Ce3+ on the two crystallographic sites in Gd2Si4N6C as compared to the Y and Lu compounds. In Ce3+/Tb3+-codoped RE 2Si4N6C (RE = Lu, Y, and Gd) phosphors, it is observed that energy transfer takes place from Ce3+ to Tb 3+ in Ce3+/Tb3+-codoped Lu2Si 4N6C and Y2Si4N6C but in the reversed direction from Tb3+ to Ce3+ in Ce 3+/Tb3+-codoped Gd2Si4N 6C, depending on the position of the 5d level of Ce3+ versus the 5D4 level of Tb3+. The potential applications of these phosphors are pointed out

Research on Temperature Control Index for High Concrete Dams Based on Information Entropy and Cloud Model from the View of Spatial Field

It is significant to adopt scientific temperature control criteria for high concrete dams in the construction period according to practical experience and theoretical calculation. This work synthetically uses information entropy and a cloud model and develops novel in situ observation data-based temperature control indexes from the view of a spatial field. The order degree and the disorder degree of observation values are defined according to the probability principle. Information entropy and weight parameters are combined to describe the distribution characteristics of the temperature field. Weight parameters are optimized via projection pursuit analysis (PPA), and then temperature field entropy (TFE) is constructed. Based on the above work, multi-level temperature control indexes are set up via a cloud model. Finally, a case study is conducted to verify the performance of the proposed method. According to the calculation results, the change law of TFEs agrees with actual situations, indicating that the established TFE is reasonable, the application conditions of the cloud model are wider than those of the typical small probability method, and the determined temperature control indexes improve the safety management level of high concrete dams. Research results offer scientific reference and technical support for temperature control standards adopted at other similar projects

Preparation and Optical Properties of Infrared Transparent 3Y-TZP Ceramics

In the present study, a tough tetragonal zirconia polycrystalline (Y-TZP) material was developed for use in high-speed infrared windows and domes. The influence of the preparation procedure and the microstructure on the material’s optical properties was evaluated by SEM and FT-IR spectroscopy. It was revealed that a high transmittance up to 77% in the three- to five-micrometer IR region could be obtained when the sample was pre-sintered at 1225 °C and subjected to hot isostatic pressing (HIP) at 1275 °C for two hours. The infrared transmittance and emittance at elevated temperature were also examined. The in-line transmittance remained stable as the temperature increased to 427 °C, with degradation being observed only near the infrared cutoff edge. Additionally, the emittance property of 3Y-TZP ceramic at high temperature was found to be superior to those of sapphire and spinel. Overall, the results indicate that Y-TZP ceramic is a potential candidate for high-speed infrared windows and domes

The Electrical and Thermal Transport Properties of La-Doped SrTiO3 with Sc2O3 Composite

Donor-doped strontium titanate (SrTiO3) is one of the most promising n-type oxide thermoelectric materials. Routine doping of La at Sr site can change the charge scattering mechanism, and meanwhile can significantly increase the power factor in the temperature range of 423–773 K. In addition, the introduction of Sc partially substitutes Sr, thus further increasing the electron concentration and optimizing the electrical transport properties. Moreover, the excess Sc in the form of Sc2O3 composite suppresses multifrequency phonon transport, leading to low thermal conductivity of κ = 3.78 W·m−1·K−1 at 773 K for sample Sr0.88La0.06Sc0.06TiO3 with the highest doping content. Thus, the thermoelectric performance of SrTiO3 can be significantly enhanced by synergistic optimization of electrical transport and thermal transport properties via cation doping and composite engineering

Photoluminescence properties of Yb2+ in CaAlSiN3 as a novel red-emitting phosphor for white LEDs

This paper reports on the diffuse reflection spectra, photoluminescence spectra and chromaticity of ytterbium in CaAlSiN3 at room temperature. It can be excited efficiently over a broad spectral range between 280 and 580 nm and exhibits a single intense red emission at 629 nm with a full width at half maximum of 75 nm due to the electronic transitions from the excited state of 4f135d to the ground state 4f14 of Yb2+. The low energy of Yb2+ emission in CaAlSiN3 can be attributed to the large nephelauxetic effect and crystal field splitting due to the coordination of Yb2+ by nitrogen. This novel developed CaAlSiN3:Yb2+, which is the first Yb2+-activated nitride red-emitting phosphor, has potential applications in spectral conversion materials for warm-white LEDs. The width of the emission band, Stokes shift and thermal quenching mechanism of Yb2+ in CaAlSiN3 and (oxy)nitride-based phosphors are discussed and compared with those of Eu2+