查看更多>>摘要：BiCuSeO exhibits remarkable low thermal conductivity among oxides. The lone pair of the Bi~(3+) and the point defects brought about by elemental doping are thought to be the origin of the low thermal conductivity. In a recent study, however, the Cu atoms in BiCuSeO play a more significant role in reducing the lattice thermal conductivity than the above two factors. In this work, two series of polycrystalline Bi_(1-x)Ca_xCu_(0.975)SeO (x = 0.025,0.050,0.075,0.100, 0.125,0.150) and Bi_(0.95)Ca_(0.05)Cu_(1-y)SeO (y = 0.015,0.025, 0.035) are synthesized by solid-state reaction. All the materials are of single phase. Point defects introduced by partial elemental substitution and atom vacancy are expected to reduce the lattice thermal conductivity, however, which is not followed by the prediction for Bi_(1-x)Ca_xCu_(0.975)SeO with 0.050 ≤ x ≤0.125 and Bi_(0.95)Ca_(0.05)Cu_(1-y) with y = 0.015,0.025, and 0.035 in the temperature range where the resistivity decreases while the thermopower increases with temperature. This is in sharp contrast with those BiCuSeO with partial elemental substitution or Cu deficiency exhibiting either both the electrical resistivity and thermopower increase or decrease with increasing temperature. Our results support that the Cu atoms in BiCuSeO play a more significant role in reducing the lattice thermal conductivity than the lone pair of the Bi~(3+) and the point defects brought about by elemental doping.
查看更多>>摘要：A binder-free positive electrode material of 3D starfish-like Co_3O_4/Ni forest is fabricated via a novel and facile hydrothermal process followed by thermal treatment. The morphological studies clearly showed the construction of starfish-like micro-flowers of Co_3O_4 nanostructure forest densely covered on the entire Ni current collector. The 3D-Co_3O_4/Ni electrode displayed an areal capacity as high as 143.28 mC cm~(-2) at 0.5 mA cm~(-2) and higher stability of 88.4% after 5000 cycles. Moreover, the fabricated 3D-Co_3O_4/Ni||3D-Bi_2O_3/Ti supercapattery delivered a maximum areal capacitance of 24.73 mF cm~(-2), the energy density of 6.73 uWh cm~(-2) and power density of 5250 uW cm~(-2) with good cycling stability > 71% capacity retention after 5000 cycles. The higher electrochemical performance of the electrode is delivered due to the availability of abundant electrochemically active sites in the 3D starfish-like Co_3O_4 microflower, which facilitates a higher electrochemical reaction. The starfish-like forest architectures allow rapid ion diffusion, and the binder-free electrode reduces the contact resistance, which fasten the electron transport. These tolerable results prompt the as-prepared electrode with 3D starfish-like Co_3O_4 microflower morphology as an auspicious positive electrode material for electrochemical energy storage devices.
查看更多>>摘要：A novel temperature stable (l-x)MgZr_(0.85)Sn_(0.15)Nb_2O_8-xBa_3Ti_4Nb_4O_(21) -2wt% BaCu(B_2O_5) (MZSN-BTN-BCB, x = 0.12, 0.14, 0.15, 0.16, 0.18 in molar) composite ceramic was fabricated via a conventional solid-state reaction method. MZSN and BTN phase can coexist in the sintered ceramics due to the different crystal structures from the results of X-Ray diffraction and scanning electron microscopy. The sintering temperature and phase composition are especially relevant to the microwave dielectric properties. The optimal sintering temperature of MZSN-BTN ceramics was successfully reduced to 1125 °C due to the formation of BCB liquid phase. The temperature coefficient of the resonant frequency was successfully adjusted to near zero by adding an appropriate amount of BTN due to its opposite-sign τf value. Excellent microwave dielectric properties of er = 33, Q×f= 53,950 GHz (at 6.079 GHz), τf = -4.3 ppm/°C were obtained in 0.88MZSN-0.12BTN-2 wt% BCB composite ceramics when sintered at 1125 °C for 4 h.
查看更多>>摘要：Spinel metal oxides, prepared at high temperature, have shown excellent gas sensing properties among metal oxide sensing materials. Herein, a series of porous spinel gallate nanospheres, including CdGa_2O_4, NiGa_2O_4, CoGa_2O_4, CuGa_2O_4, ZnGa_2O_4, and MgGa_2O_4 were prepared by solvothermal method and followed low temperature calcination. XRD, SEM, XPS and N_2 adsorption-desorption have been carried out to determine their structure, morphology, chemical state and surface area, respectively. These nanospheres are all composed of tiny nanoparticles, giving meso-porous characters. Furthermore, the sensor based on CdGa_2O_4 exhibits excellent formaldehyde sensing performance, including good selectivity, short response time, and excellent stability at the low working temperature of 120 °C.
查看更多>>摘要：A series of NaYF_4:0.2Yb/0.02Ho microcrystals co-doped with various K~+ and Gd~(3+) concentrations were synthesized by hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and upconversion (UC) spectroscopy were used to study the effects of co-doped ions on the phase structure, morphology, size and up-conversion luminescence (UCL) properties of microcrystals in detail. The results show that the K~+ and Gd~(3+) co-doping do not evoke the change in crystal structure, but the UCL intensities of NaYF_4:0.2Yb/0.02Ho are significantly enhanced. Compared to K~+ and Gd~(3+)-absent sample, UCL intensities of green emission (541 nm) and red emission (643 nm) in NaYF_4:0.2Yb/0.02Ho microcrystals via 15 mol% K~+ and 15 mol% Gd~(3+) co-doping are increased by 2.4 times and 3.3 times, respectively. The temperature sensing characteristics and thermal quenching properties of the microcrystals were also explored. Significantly, the maximum relative sensitivity of the studied sample reaches 0.0127 K~(-1) at 298 K, which indicates that NaYF_4:0.2Yb/0.02Ho phosphors can be suitable for temperature sensing.
查看更多>>摘要：Semiconductor catalyst with high photocatalytic activity can be exploited via heterojunction. In this study, a new S-scheme SrTiO_3/porous ZnO composite was rationally devised, successfully prepared by utilizing a two-step pyrolysis of SrTiO_3/ZIF-8, and analyzed by various characterization technologies including XRD, SEM, TEM, BET, XPS, PL, UV-vis DRS, and photoelectrochemical and DFT theoretical calculations. A porous structure, tight contact, and a heterojunction formed between SrTiO_3 and porous ZnO (ZnOT) can be observed by SEM and TEM images. BET testing indicates that the SrTiO_3/porous ZnO composite (S3ZT) shows the highest specific surface area (30.37 m~2/g). The band gap values (E_g) of SrTiO_3 and ZnOT are around 3.17 and 2.95 eV, which agree with those obtained from DFT calculations. Compared to other samples, the SrTiO_3/porous ZnO composite (S3ZT) shows higher light absorption and lower transfer resistance as demonstrated by UV-vis DRS and EIS results. S3ZT presents a superior photocatalytic efficiency of 48.8% in degrading 5 mg/L methyl orange (MO) irradiated by 1 h UV-vis light, which are 7- and 1.5-fold higher than pristine SrTiO_3 and ZnOT, respectively. Moreover, based on Mott-Schottky theory, active species trapping experiments, XPS determination, and DFT calculations (energy band gap and work function), it was shown to be reasonable to utilize the S-scheme charge migration process for an explanation regarding the better photocatalytic activity of SrTiO_3/porous ZnO composite. Overall, this work will provide an effective protocol for devising and preparing semiconductor photocatalysts with S-scheme heterojunction by utilizing the superior characteristics of MOFs.
查看更多>>摘要：Tin sulfide (SnS_x) thin films deposited by atomic layer deposition (ALD) under various deposition conditions have unique properties. Such films have two phases, tin monosulfide (SnS) and tin disulfide (SnS_2), that depend on the composition ratio of the thin film, and these materials can be applied to a wide range of technologies, such as solar cells, optical sensors, and transistors. In this study, we deposit amorphous tin sulfide thin films at 100 °C using ALD and perform post annealing at various temperatures to control the phase transition from SnS_2 to SnS. The post annealing temperature-dependent phase transition was analyzed through Raman spectroscopy, grazing-incidence X-ray diffraction (GI-XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) spectroscopy, and ultraviolet photoelectron spectroscopy (UPS). Thermodynamic calculations were performed to determine that the initial temperature of the phase transition correspond to the post annealing temperature of 350 °C. The phases and crystal structures of the films annealed at different temperatures were investigated by Raman and GI-XRD. The chemical bonding of the films was analyzed through XPS, revealing that the binding energy of Sn~(4+) states shifted to the lower binding energy of Sn~(2+) states with increasing annealing temperatures. The electronic band structures of the films were calculated by UV-vis and UPS. The band gaps of the 300 °C, 350 °C, 400 °C annealed films were 2.26 eV, 2.05 eV, 1.63 eV, respectively. The tin sulfide thin films had n-type characteristics when annealed at 300 °C, which changed to p-type characteristics when annealed at 350 °C and 400 °C. Through this study, we can investigate phase transition of tin sulfides and correlate fabrication conditions to both n-type and p-type characteristics, which can be applied to synthesize the desired films for application in various devices.
查看更多>>摘要：The aim of this work was to propose the experimental partial isothermal section of the Al-Pd-Co phase diagram at 1035 °C and to study the structure of quasicrystalline approximant ε_n. Scanning electron microscopy including energy dispersive X-ray spectroscopy, X-ray diffraction and scanning transmission electron microscopy were used in the investigation. Calculation of atomic structures was performed using Monte Carlo simulation minimising Empirical Oscillating Pair Potentials energy. Besides the proposed partial isothermal section at 1035 °C, homogeneity ranges of phases ε_n, U, F, V,δ, and W were schematically projected. Various modifications of ε_n were observed and/or identified in the investigated alloys. The structures of ε_(22) and ε_(34) were experimentally observed in the Al-Pd-Co system for the first time. Furthermore, their atomic structure models were created. Last but not least, it was experimentally documented that the regular arrangement of tiles in ε_n structures can be interrupted by structural defects. The obtained results form a comprehensive picture of the individual structural modifications of the ε_n phase.
查看更多>>摘要：Catalytic oxidation has been considered as one of the most promising strategies for the removal of indoor HCHO which causes multiple health problems. Alloyed Au-Pt showed potential for catalytic oxidation reactions, but the reports on HCHO oxidation are limited. In addition.understanding on the catalytic mechanism is lacking. In this work, a sodium citrate assistant photodeposition process was developed to fabricate highly dispersed dual Au-Pt alloy with 2-3 nm on the surface of TiO_2. The turnover frequency of Au-Pt/TiO_2 (68.6 h~(-1)) is much higher than that of Pt/TiO_2 (19.9 h~(-1)). This enhancement was also confirmed on different TiO_2 supports and with different Pt loading. Based on the experimental and density functional theory calculations, it was found that the alloyed Au-Pt has more metallic Pt and is beneficial for the adsorption and dissociation of oxygen. Therefore, the rapid conversion of dioxymethylene species to formate species, with reduced reaction barrier, promotes the performance in catalytic oxidation of HCHO.
查看更多>>摘要：La-doped CeO_2 nanoparticles of composition Ce_(1-x)La_xO_(2-δ) (0 ≤ x ≤ 0.1) have been studied here as prospective electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs). They were synthesized by auto-combustion method and the powder samples were calcined at 700 °C to get ultrafine nanocrystalline particles. They were characterized by XRD, Raman, FTIR, XPS, DRS, FESEM/EDX, particle size analyzer and ac-impedance techniques. Ionic conductivity was measured from 350 - 750 °C. The Ce_(0.90)La_(0.10)O_(2-δ) (0.1 LDC) and Ce_(0.95)La_(0.05)O_(2-δ) (0.05 LDC) showed a maximum conductivity of 8.89 ×10~(-3) and 8.32 ×10~(-3) S cm~(-1) at 700 °C, respectively. The σt of 0.1 LDC = 1.01 ×10~(-2) S cm~(-1) at 750 °C. The activation energy of 0.1 LDC and 0.05 LDC was found to be 0.70 eV and 0.87 eV, respectively. These values are higher than those reported for La-doped CeO_2 in literature. The SOFC performance with 0.05 LDC as electrolyte showed open circuit voltage of 0.81 V and maximum power density of 41 mW cm~(-2) at 650 °C using hydrogen as fuel.
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