First-principles calculations of the YBa2Cu3O7/PrBa2Cu3O7 interface

We discuss results of spin-polarized electronic structure calculations for a 1 × 1 YBa₂Cu₃O₇/PrBa₂Cu₃O₇ supercell, obtained by the full-potential linear augmented plane wave (FLAPW) method as implemented in the WIEN2k package. The calculations are based on the generalized gradient approximation for the exchange correlation functional. The on-site Coulomb interaction of the correlated Cu 3d and Pr 4f electrons is considered by using the LSDA+U approach. The electronic states of the YBa₂Cu₃O₇/PrBa₂Cu₃O₇ interface are compared with the respective states in the PrBa₂Cu₃O₇ and YBa₂Cu₃O₇ bulk compounds, where we focus on the magnetic Pr atoms and the Cu atoms in the CuO₂ planes.     

Nanoplates of α-SnWO4 and SnW3O9 prepared via a facile hydrothermal method and their gas-sensing property

Nanoplates of α-SnWO₄ and SnW₃O₉ were selectively synthesized in large scale via a facile hydrothermal reaction method. The final products obtained were dependent on the reaction pH and the molar ratio of W⁶⁺ to Sn²⁺ in the precursors. The as-prepared nanoplates of α-SnWO₄ and SnW₃O₉ were characterized by X-ray powder diffraction (XRD), N₂-sorption BET surface area, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The XPS results showed that Sn exists in divalent form (Sn²⁺) in SnW₃O₉ as well as in α-SnWO₄. The gas-sensing performances of the as-prepared α-SnWO₄ and SnW₃O₉ toward H₂S and H₂ were investigated. The hydrothermal prepared α-SnWO₄ showed higher response toward H₂ than that prepared via a solid-state reaction due to the high specific surface area. The gas-sensing property toward H₂S as well as H₂ over SnW₃O₉ was for the first time reported. As compared to α-SnWO₄, SnW₃O₉ exhibits higher response toward H₂S and its higher response can be well explained by the existence of the multivalent W (W⁶⁺/W⁴⁺) in SnW₃O₉.     

Plasma enhanced-CVD of undoped and fluorine-doped Co3O4 nanosystems for novel gas sensors

Co₃O₄-based nanosystems were prepared on polycrystalline Al₂O₃ by plasma enhanced-chemical vapor deposition (PE-CVD), at temperatures ranging between 200 and 400 °C. The use of two different precursors, Co(dpm)₂ (dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) and Co(hfa)₂·TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine) enabled the synthesis of undoped and fluorine-doped Co₃O₄ specimens, respectively. A thorough characterization of their properties was performed by glancing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), field emission-scanning electron microscopy (FE-SEM), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). For the first time, the gas sensing properties of such PE-CVD nanosystems were investigated in the detection of ethanol and acetone. The results show an appreciable response improvement upon doping and functional performances directly dependent on the fluorine content in the Co₃O₄ system.     

Thermodynamic investigation on the Al2O3–BaO binary system

The Al₂O₃–BaO binary system has been studied using the CALPHAD technique in this paper. The modeling of Al₂O₃ in the liquid phase is modified from the traditional formula with the liquid phase represented by the ionic two-sublattice model as (Al³⁺, Ba²⁺)_P (AlO₂¹⁻, O²⁻)_Q. Based on the measured phase equilibrium data and experimental thermodynamic properties, a set of thermodynamic functions has been optimized using an interactive computer-assisted analysis. A comparison between the calculated results and experimental data is presented.     

Catkin liked nano-Co3O4 catalyst built-in organic microreactor by PEMOCVD method for trace CO oxidation at room temperature

In this paper, tricobalt tetraoxide (Co₃O₄) catalyst was coated on the polydimethylsiloxane microchannel by the plasma-enhanced metal-organic chemical vapor deposition technology. The obtained Co₃O₄ film was characterized by SEM, XRD, XPS, and TEM, and the results show that the as-deposited Co₃O₄ film was initially composed of many cauliflowers-shaped microclusters. Also, the microcauliflower was transformed from an amorphous phase to a crystal phase when the Co₃O₄ film was treated by Ar and O₂ plasma for more than 20 min, and the crystal lattice line occurred on the surface of nano-sized-Co₃O₄ particles. Meanwhile, the interface of Co₃O₄ particles with diameter between 3 and 12 nm became obvious and some nano-catkin structures were also formed on the Co₃O₄ film. The ratio of Co³⁺/Co²⁺ in the spinel-type Co₃O₄ was nearly 2, and the nano-particles predominantly expose their {311}, {111}, and {220} planes. These morphologies and structure characteristics were found to be ideal for increasing the catalytic activity efficiency of Co₃O₄ for CO oxidation, and the catalytic stability of Co₃O₄ coated on the organic microreactor lasted nearly 85 h for trace CO oxidation at room temperature.     

Mechanism of CO and O3 sensing on WO3 surfaces: First principle study

The microscopic mechanism of O₃ and CO sensing on WO₃ surfaces is clarified by a first principle study. It is shown that ozone reduces to O₂ on the (0 0 1) surface of WO₃ decreasing in such a way the number of oxygen vacancies and the conductivity (since oxygen vacancies act as donors in WO₃). The mechanism of CO sensing is just the opposite: the CO molecule is oxidized to CO₂ on the WO₃ surface increasing the number of oxygen vacancies and the conductivity. The reaction enthalpy for the reduction process of O₃ is found to be −2.54 eV in local density approximation (LDA) and −2.86 in generalized gradient approximation (GGA). The corresponding values for CO are −1.73 eV (LDA) and −1.52 eV (GGA). The adsorptions of O₃ and CO without reduction or oxidation are also calculated but the related energies are much smaller.     

Optical temperature sensing behavior of enhanced green upconversion emissions from Er-Mo:Yb2Ti2O7 nanophosphor

The Er-Mo:Yb₂Ti₂O₇ nanocrystalline phosphor has been prepared by sol-gel method and used as an optical thermometry. By Mo codoping, the green upconversion (UC) emission intensity increased about 250 times than that of Er:Yb₂Ti₂O₇ under a 976 nm laser diode excitation. It indicates that such green enhancement arises from the high excited state energy transfer (HESET) with the |²F_7/2, ³T₂> state of Yb³⁺-MoO₄²⁻ dimer to the ⁴F_7/2 level of Er³⁺. The fluorescence intensity ratio (FIR) of the two green UC emissions bands was studied as a function of temperature in a range of 290-610 K, and the maximum sensitivity and the temperature resolution were approximately 0.0074 K⁻¹ and 0.1 K, respectively. It suggests that the Er-Mo:Yb₂Ti₂O₇ nanophosphor with a higher green UC emissions efficiency is a promising prototype for applications in optical temperature sensing.     

Rare‐earth materials for use in the dark

Abstract— Recently, it was found that some materials doped with rare‐earth ions show bright and long‐lasting phosphorescence. They do not include radioactive elements and can be safely used as luminous paints for use in the dark. Some of them are better than the traditional zinc sulfide doped with copper (ZnS:Cu). The most important rare‐earth materials with long‐lasting phosphorescence are aluminates such as alkaline‐earth aluminates MAl₂O₄:Eu²⁺, Dy³⁺ (M = Sr, Ca) and garnets Y₃Ga₅O₁₂:Tb³⁺, Gd₃Ga₅O₁₂:Tb³⁺, Cd₃Al₂Ge₃O₁₂:Tb³⁺, Cd₃M₂Ge₃O₁₂:Pr³⁺ (M = Al, Ge), Y₃Al_5?xGa_xO₁₂:Ce³⁺ (x = 3, 3.5). Some oxides such as InBO₃:Tb³⁺, Ba₂SiO₄:Dy³⁺ also show long‐lasting phosphorescence properties. Other sulfide materials include ZnS:Eu, Ca_xSr_1?x S:Bi, Tm, Cu or Ca_xSr_1?xS:Eu. Alkaline‐earth aluminates MAl₂O₄:Eu²⁺ (M = Mg, Ca, Sr, Ba) codoped with RE³⁺ (RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized by using homogeneous precipitation method.     

Synthesis of nearly monodisperse Co3O4 nanocubes via a microwave-assisted solvothermal process and their gas sensing properties

Nearly monodisperse Co₃O₄ nanocubes have been prepared by a microwave-assisted solvothermal (MS) method at 180 °C for 20 min. The samples are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern and TEM images of the products illustrated that Co₃O₄ nanocubes had a cubic phase with a lateral size of ∼20 nm. The gas response of the Co₃O₄ nanocubes was studied to several typical organic gases. The Co₃O₄ nanocubes showed good gas sensing performance towards xylene and ethanol vapors with rapid and high responses at a low-operating temperature. The results showed that the Co₃O₄ nanocubes can be used to fabricate high performance gas sensors.     

Gas sensitivity of Zn doped α-Fe2O3(SO4, Sn, Zn) to carbon monoxide

It is shown that the doping of Zn and Sn can improve the gas sensitivity of α-Fe₂O₃-based sensing material to CO. X-ray photo-electron spectroscopy analysis suggests that this is mainly due to the fact that the simultaneous doping of Zn and Sn can increase the S and hence SO₄²⁻ contents in the α-Fe₂O₃(SO₄²⁻, Sn, Zn) sensing material. The results also suggest that under a given condition, the gas sensitivity of α-Fe₂O₃(SO₄²⁻, Sn, Zn) to CO can be optimised by properly adjusting the doped Zn content.     

Synthesis of Bi and Gd doped ZnB2O4 for evaluation as potential materials in luminescent display applications

A series of Bi³⁺ and Gd³⁺ doped ZnB₂O₄ phosphors were synthesized with solid state reaction technique. X-ray diffraction technique was employed to study the structure of prepared samples. Excitation and emission spectra were recorded to investigate the luminescence properties of phosphors. The doping of Bi³⁺ or Gd³⁺ with a small amount (no more than 3 mol%) does not change the structure of prepared samples remarkably. Bi³⁺ in ZnB₂O₄ can emit intense broad-band purplish blue light peaking at 428 nm under the excitation of a broad-band peaking at 329 nm. The optimal doping concentration of Bi³⁺ is experimentally ascertained to be 0.5 mol%. The decay time of Bi³⁺ in ZnB₂O₄ changes from 0.88 to 1.69 ms. Gd³⁺ in ZnB₂O₄ can be excited with 254 nm ultraviolet light and yield intense 312 nm emission. The optimal doping concentration of Gd³⁺ is experimentally ascertained to be 5 mol%. The decay time of Gd³⁺ in ZnB₂O₄ changes from 0.42 to 1.36 ms.     

Potentiometric solid-state sensor for DO measurement in water using sub-micron Cu0.4Ru3.4O7 + RuO2 sensing electrode

The dissolved oxygen (DO) sensing electrode (SE) concept utilizing sub-micron-sized ruthenium oxide (RuO₂), doped with other nanostructured oxides, has been extended to investigate the possibility of employing copper (II) oxide (Cu₂O) as a dopant in order to improve sensor's characteristics and meet long term antifouling needs for SEs. In this work, a thin-film SE made of RuO₂ was constructed on the alumina sensor substrate, and a range of dopants and their concentrations was added to it in order to optimize SE properties. The Cu₂O-doped RuO₂ SE had shown a linear response to DO between 0.5 and 8.0 ppm at various temperatures, with two sensitivity maxima of 47.4 and 46.0 mV per decade for Cu₂O concentrations of 10 and 20 mol%, respectively. The maximum sensitivity for Cu_0.4Ru_3.4O₇ + RuO₂-SE was obtained at a dopant concentration of 10%. Selectivity measurements revealed that the presence of Ca²⁺, Mg²⁺, Li⁺, Na⁺, NO³⁻, PO₄³⁻, SO₄²⁻, F⁻, K⁺ and Cl⁻ in the solution had no significant effect on the sensor's emf. The sensor allows overcoming the problem of an insufficient selectivity of semiconductor-based water sensors. It was also found that the doping of RuO₂-SE by Cu₂O allowed it to function at full capacity in a natural outdoor water body with no obvious effects of biofouling.     

Influence of doping BiYO3 and Nb2O5 on PTCR characteristics of BaTiO3 thermistor ceramics

Nb₂O₅-doped (1 − x)Ba_0.96Ca_0.04TiO₃-xBiYO₃ (where x = 0.01, 0.02, 0.03 and 0.04) lead-free PTC thermistor ceramics were prepared by a conventional solid state reaction method. X-ray diffraction, scanning electron microscope, Agilent E4980A and resistivity-temperature measurement instrument, were used to characteristic the lattice distortion, microstructure, temperature dependence of permittivity and resitivity-temperature dependence. It was revealed that the tetragonality c/a of the perovskite lattice, the microstructure and the Curie temperature changed with the BiYO₃ content. In order to decrease the room temperature resistivity, the effect of Nb₂O₅ on the room temperature resistivity was also studied, and its optimal doping content was finally chosen as 0.2 mol%. The 0.97Ba_0.96Ca_0.04TiO₃-0.03BiYO₃-0.002Nb₂O₅ thermistor ceramic exhibited a low ρ_RT of 3.98 × 10³ Ω cm, a typical PTCR effect of ρ_max/ρ_min > 10³ and a T_c of 153 °C.     

Modeling surface complexation at the colloid/electrolyte interface

A computer program was developed to model the electrical double and triple layer on amphoteric oxide surfaces. It was tested for the adsorption of Co²⁺ ions on colloidal spherical hematite (α-Fe₂O₃) particles in a NaNO₃ suspension. The procedure is general and with a few modifications the program can be applied to other chemical equilibrium problems.     

A new long-lasting phosphor Zr and Eu co-doped SrMg2(PO4)2

Zr⁴⁺- and Eu³⁺-codoped SrMg₂(PO₄)₂ phosphors were prepared by conventional solid-state reaction. Under the excitation of ultraviolet light, the emission spectra of Sr_0.95Eu_0.05Mg_2−2xZr_2xP₂O₈ (x = 0.0005-0.07) are composed of a broad emission band peaking at 500 nm from Zr⁴⁺-emission and the characteristic emission lines from the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3 and 4) transitions of Eu³⁺ ions. These phosphors show the long-lasting phosphorescence. The emission color varies from red to white with increasing Zr⁴⁺-content. The white-light emission is realized in single-phase phosphor of Sr_0.95Eu_0.05Mg_2−2xZr_2xP₂O₈ (x = 0.07) by combining the Zr⁴⁺- and Eu³⁺-emission. The duration of the persistent luminescence of Sr_0.95Eu_0.05Mg_2−2xZr_2xP₂O₈ (x = 0.07) reaches nearly 1.5 h. The time at which the long-lasting phosphorescence intensity is 50% of its original value (T_0.5) is 410 s. The afterglow decay curves and the thermoluminescence spectra were measured to discuss this long-lasting phosphorescence phenomenon. The co-doped Zr⁴⁺ ions act as both the luminescence centers and trap-creating ions.     

Calculation of ternary mixing properties of melts and minerals from the bounding binaries

Among the several methods that have been used to predict thermodynamic properties of ternary alloys and oxides from three binary data, we used the models proposed by Kohler(1), Toop(2), and Muggianu (3) in order to evaluate the possibility of the application of these methods to geologically important systems, such as zeolites, clay minerals and silicate glasses. These models can represent the ternary excess Gibbs energy of the NaCl-KCl-H₂O and Ca-Mg-Fe²⁺ garnet (Ca₃Al₂Si₃O₁₂ - Mg₃Al₂Si₃O₁₂ - Fe₃Al₂Si₃O₁₂) systems relatively well without a ternary correction term. The deviation from the reference data increases in the central region of the composition triangle. Toop's model with constant mole fractions of NaCl and Mg best simulated the ternary systems among the models. The path independent Muggianu model was applied to diopside (CaMgSi₂O₆) -jadeite (NaAlSi₂O₆) - acmite (NaFe³⁺Si₂O₆) ternary as an example. Although there exists intrinsic uncertainty in calculation without the ternary interaction term, these models, especially, Muggianu and Kohler can be good approximation methods for prediction of the ternary excess properties of the natural mineral solid solutions, devoid of ternary experimental thermodynamic data.     

Preparation and characterization of nanocrystalline α-Fe2O3 by a sol-gel process

α-Fe₂O₃ ultra-fine powder with an average particle size of 6–26nm has been prepared by a sol-gel process. Thermal analysis, X-ray diffraction and transmission electron microscope were used to study its formation process and micro-structure. The temperature dependence of the electric conductance of the elements made of nanocrystalline α-Fe₂O₃ shows that the gas-sensing properties are strongly related to its surface. The elements exhibited good sensitivity and selectivity to ethyl alcohol, indicating it is a promising alcohol-sensing material.     

P2-Packing问题参数算法的改进

P₂-Packing问题是一个典型的NP难问题.目前这个问题的最好结果是时间复杂度为O^*(2^5.301k)的参数算法,其核的大小为15k.通过对P₂-packing问题的结构作进一步分析,提出了改进的核心化算法,得到大小为7k的核,并在此基础上提出了一种时间复杂度为O^*(2^4.142k)的参数算法,大幅度改进了目前文献中的最好结果.     

Experimental study and thermodynamic optimization of the ZnO–FeO–Fe2O3–CaO–SiO2 system

Liquidus phase equilibrium experimental data from the present study for the ZnO-“Fe₂O₃”-CaO-SiO₂ system in air, combined with phase equilibria and thermodynamic data from the literature on the ZnO-“Fe₂O₃”-CaO system in air and ZnO-“FeO”-CaO-SiO₂ system in equilibrium with metallic Fe, have been used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in the ZnO–FeO–Fe₂O₃–CaO–SiO₂ system. The modified quasichemical model is used for the liquid slag phase; spinel (Fe,Zn,Ca)^tetr (Fe,Zn,Ca,Va)^oct₂O₄, melilite Ca₂(Fe²⁺,Fe³⁺,Zn)(Fe³⁺,Si)₂O₇ and olivine (Fe,Zn,Ca)^I(Fe,Zn,Ca)^IISiO₄ are described with compound energy formalism; lime and wustite (monoxide) (Ca,Fe,Zn)O, zincite (Zn,Fe,Ca)O_1+x, calcium-zinc ferrites Ca₂Fe₂O₅-“CaZnO₂” and CaFe₄O₇-“ZnFe₄O₇”, α- and α′-dicalcium silicate (Ca,Fe,Zn)₂SiO₄ and tricalcium silicate (Ca,Fe,Zn)₃SiO₅ and silicoferrite of calcium (SFC) Ca₉Fe₄₆SiO₈₀–Ca₁₂Fe₄₀Si₄O₈₀ are described within Bragg-Williams formalism; for other phases, previous assessments have been adopted. The phase diagrams are back calculated with the optimized model parameters. Present study is a part of research program on the characterization of the multicomponent PbO–ZnO–FeO–Fe₂O₃-“Cu₂O”-CaO-SiO₂ system.