Stability and formability of complex oxides in M2O3–M′2O3 systems

Based on fundamental thermodynamics and a simple energy model for solid M₂O₃ oxides, two atomic parameters of their constituent elements are identified that govern the solid phase stability in an M₂O₃–M₂′O₃ binary system. They are P₁=|r_A−r_B| and P₂=(r_A+r_O)(r_B+r_O)(r_A+r_B+2r_O), where, r_A, r_B and r_O are the ionic radii of ion A, ion B and oxygen, respectively. Using 237 known M₂O₃–M₂′O₃ systems and these two parameters (P₁ and P₂), new rules were obtained not only on the formability of stable complex oxides but also on the conditions that these compounds being of MM′O₃ stoichiometry and further of ABO₃-type perovskite structure. The classification accuracy of such rules reaches respectively 98.7% for formability of complex oxides, 97.9% for the MM′O₃ stoichiometry test, and 100% for the ABO₃-type perovskite structure prediction. Thirty seven new systems are used to validate these empirical rules, and the prediction is in good agreement with experiment. The influence of ionic size difference on the phase stability is further discussed based on the proposed energy model. The new rules may help material scientists to practically predict new complex compounds as well as to further theoretically study phase stability in M₂O₃–M₂′O₃ systems.     

Thermodynamic description of the Al-Li-Zn system

The Al-Li-Zn system was critically assessed using the CALPHAD technique. The solution phases (liquid, bcc, fcc and hcp) were described by the substitutional solution model. The compounds Al₂Li₃ and Al₄Li₉ in the Al-Li system had homogeneity ranges of Zn and were treated as (Al,Zn)₂Li₃ and (Al,Zn)₄Li₉ in the Al-Li-Zn system, respectively. The compounds αLi₂Zn₃, βLi₂Zn₃, αLi₂Zn₅, βLi₂Zn₅ and αLiZn₄ in the Li-Zn system had no solubility of the third component Al in the Al-Li-Zn system. A two-sublattice model (Al,Li,Zn)_0.2(Al,Li,Zn)_0.8 was applied to describe the compound βLiZn₄ in the Al-Li-Zn system in order to cope with the order-disorder transition between hexagonal close-packed solution (hcp-A3) and βLiZn₄ with the Mg-type structure. The ternary compound τ₂ with a NaTl-type structure (B32) had the same structure with the compounds AlLi in the binary Al-Li system and LiZn in the binary Li-Zn system. In the present work, the three compounds AlLi, LiZn and τ₂ were treated as one phase by a two-sublattice model (Al,Li,Zn)_0.5(Al,Li,Zn)_0.5 in order to cope with the order-disorder transition between B32(AlLi, LiZn and τ₂) and body-centered cubic solid solution (bcc-A2). The ternary intermetallic compounds τ₁ and τ₃ in the Al-Li-Zn system were treated as the formula Li(Al,Zn)₂ and (AlLi,Zn)Zn₃, respectively. A set of self-consistent thermodynamic parameters describing the Gibbs energy of each individual phase as a function of composition and temperature in the Al-Li-Zn system was obtained.     

Thermodynamic assessment of the KCl–K2CO3–NaCl–Na2CO3 system

Phase equilibria and thermodynamic properties of the KCl–K₂CO₃–NaCl–Na₂CO₃ system were analyzed on the basis of the thermodynamic evaluation of the KCl–NaCl,KCl–K₂CO₃,NaCl–Na₂CO₃,K₂CO₃–Na₂CO₃ and KCl–K₂CO₃–NaCl–Na₂CO₃ systems. The Gibbs energies of individual phases was approximated by two-sublattice models for ionic liquids and crystals. Most of the experimental information was well described by the present set of thermodynamic parameters. The lowest monovariant eutectic temperature in the KCl–NaCl–Na₂CO₃ system is located at 573 ^°C, with a composition of X_Na2CO3=0.31,X_KCl=0.35 and X_NaCl=0.34.     

飞机跑道胶痕的自动识别系统设计与实现

为了减轻机场跑道除胶工作人员的劳动强度,提高除胶工作效率,文章提出了一种基于机器视觉的胶痕自动查找和识别方法,设计了基于ARM单片机控制的图像无线采集和基于PC机控制的图像接收、图像预处理和图像识别系统;文章通过分析预处理后的数据特点,确定了基于细胞神经网络算法的胶痕识别算法,然后在MATLAB仿真环境下确定了该算法的最优模型和参数,最后在Visual C++6.0环境下完成了该算法的程序编译,调试并完成了对胶痕的自动识别过程;理论仿真和程序测试的结果证明了文章提出的方法在胶痕自动识别系统中的可行性,也为机场特种设备的无人化和智能化提供了参考。     

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.     

Thermodynamic assessment of the Ga–Gd,Ga–Nb and Gd–Nb binary phase diagrams towards the Ga–Gd–Nb system

The present work gives a thermodynamic optimization of the Ga–Gd, Ga–Nb and Gd–Nb binary systems based on the CALPHAD method. Redlich-Kister polynomials are used to describe the excess Gibbs energy of the liquid phase and the solid solutions. The Ga₂Gd (ϵ) and GaNb₃ (A15) phases, which present a large homogeneity range, were described using a two-sublattice model with the formula (Ga)₂(Ga,Gd)₁ and (Nb)₃(Ga,Nb)₁ respectively. The remaining intermediate phases, ht_Ga₄Nb, Ga₃Nb, Ga₁₃Nb₅, Ga₅ Nb₄, Ga₄ Nb₅, Ga₃Nb₅, Ga₆Gd, GaGd, Ga₂Gd₃ and Ga₃Gd₅, were treated as stoichiometric compounds. The generated thermodynamic parameters relative to the involved phases were critically discussed and used to build the Ga-Gd-Nb ternary system.     

Modeling of thermodynamic properties of ABr-PrBr3 (A=Li-Cs ) systems

The thermodynamic properties of ABr-PrBr₃(A=Li-Cs) systems were assessed by the CALPHAD method. The liquid phase in the systems was described by the non-stoichiometric associate model. The entropies of mixing in the liquid were evaluated from experimental liquidus and enthalpy of mixing data. For the pseudobinary compounds A₃PrBr₆,APr₂Br₇, and A₂PrBr₅ (A=K,Rb) and Cs₃PrBr₆ and CsPr₂Br₇, the dependences of Gibbs energies of formation on temperature were calculated. The anomalies of sequences of thermodynamic properties in RbBr-PrBr₃ were observed and discussed. The nature of the liquid phase and precision of calculations of the Rb₂PrBr₅(s) compound were discussed.     

Identification of charge‐transfer transition between Gd3+ to O2− in gadolinium‐containing oxide phosphors in VUV region

Abstract— The broad bands at around 155 nm for GdAl₃(BO₃)₄:Eu, at 184 nm for Ca₄GdO(BO₃)₃:Eu, at 183 nm for Gd₂SiO₅:Eu, and at 170 nm for GdAlO₃:Eu were observed. These bands were assigned to the charge‐transfer (CT) transition of Gd³⁺‐O^2?. In the excitation spectrum of (Gd,Y)BO₃:Eu, a broadened excitation band was observed in VUV region. It could be considered that this band was composed of two bands at about 160 and 166 nm. The preceding band was assigned to the BO₃ group absorption. The later one at about 166 nm could be assigned to the CT transition of Gd³⁺‐O^2?, according to the result of GdAl₃(BO₃)₄:Eu, Ca₄GdO(BO₃)₃:Eu, Gd₂SiO₅:Eu, and GdAlO₃:Eu. The excitation spectra overlapped between the CT transition of Gd³⁺‐O^2? and BO₃ groups absorption. It caused the emission of Eu³⁺ to take place effectively in the trivalent europium‐doped (Gd,Y)BO₃ host lattice under 147‐nm excitation.     

CALPHAD: Phase diagram of the system KFK2MoO4SiO2

The phase diagrams of the binary systems KFK₂MoO₄, KFSiO₂, and K₂MoO₄SiO₂, as well as that of the ternary system KFK₂MoO₄SiO₂ in the range up to 50 mole % SiO₂, were measured using the thermal analysis method. The thermodynamically consistent phase diagrams were calculated using the coupled analysis of the thermodynamic and phase diagram data.In the system KFK₂MoO₄ the intermediate compound K₃FMoO₄, melting congruently at 751 °C, is formed. This compound divides this system into two simple eutectic ones. The coordinates of the individual eutectic points are: E₁: 30.5 mole % K₂MoO₄, 720.4 °C, and E₂: 58.8 mole % K₂MoO₄, 744.9 °C. In the binary system KFSiO₂ the liquidus curve of KF shows an inflex point, characteristic for reciprocal systems with chemical reaction taking place between components. Similar course of the liquidus curve of K₂MoO₄ was found in the binary system K₂MoO₄SiO₂, indicating the presence of the chemical reaction between components as well. The strong positive deviation from ideal behavior of the ternary system KFK₂MoO₄SiO₂ was ascribed to the possible formation of heteropolyanions [SiMo₁₂O₄₀]⁴⁻ in the melt.In the investigated concentration range of the ternary system no eutectic point has been found. It lies most probably beyond the investigated part of the system. The standard deviation of approximation of the calculated ternary phase diagram is ± 5.9 °C, which is approximately on the same level of magnitude as the estimated experimental error of ± 4 °C.     

Thermodynamic evaluation and optimization of LiNO3–KNO3–NaNO3 ternary system

The phase diagram of LiNO₃–KNO₃ system was investigated with differential scanning calorimetry. Phase transitions data of LiNO₃–KNO₃ system were obtained. Using the measured phase equilibrium data as well as other available phase equilibrium and thermodynamic data in literature, the thermodynamic optimization of parameters for all phases and compounds in the LiNO₃–NaNO₃–KNO₃ system was performed. The Modified Quasichemical Model was applied for the liquid phase, and Compound Energy Formalism was used for the NaNO₃–KNO₃ solid solutions. The compound KNO₃·LiNO₃ was treated with Neumann-Kopp rule. The optimized parameters were used to predict the phase diagram of LiNO₃–NaNO₃–KNO₃ ternary system and the predicted ternary invariant points were experimentally verified.     

Thermodynamic properties of sodium pyrovanadate (Na4V2O7) at high temperature (298.15–873 K)

The sodium pyrovanadate (Na₄V₂O₇) powder was synthesized by solid-state reaction using sodium carbonate (Na₂CO₃) and vanadium pentoxide (V₂O₅) as raw materials. X-ray powder diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimeter (DSC) were used to accurately characterize the synthesized sample. The solid-state phase transformation from α-Na₄V₂O₇ to β-Na₄V₂O₇ occurs at the temperature 696 K and the enthalpy is equals to 1.03 ± 0.01 kJ/mol, the endothermic effect at 931 K and the enthalpy is equals to 31.35 ± 0.31 kJ/mol, which is related to the melting of Na₄V₂O₇. The high-temperature heat capacity of Na₄V₂O₇ was measured using a Multi-high temperature calorimeter 96 line and DSC. The obtained high-temperature heat capacity of Na₄V₂O₇, as a function of temperature, was modeled as: Cp=314.62+0.05T-5494390T^-2 J·mol^-1·K^-1 (298.15-873 K). The temperature dependence on heat capacity was then used for computing changes in the enthalpy, entropy, and Gibbs free energy at the specific temperature internal.     

Influences of substituting Na+ ions in Eu2+, Mn2+ doped Ba9Y2Si6O24 phosphors

Near-ultraviolet (NUV)-excitable phosphors composed of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0–0.8) and Ba_8.7-qNa_0.4Eu_0.1Mn_qY₂Si₆O₂₄ (q = 0–0.4) were prepared via a solid-state reaction in a reducing atmosphere. The X-ray diffraction patterns of the obtained phosphors were examined to index the peak positions. After Na⁺ substitution for Ba²⁺ in the Ba_8.9Eu_0.1Y₂Si₆O₂₄ host lattice, the clear shift from green to yellow emission was observed. The Gaussian components of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0, 0.4, and 0.8) phosphors were exploited by using the three different Eu²⁺ ion sites in the host lattice. The dependence of the luminescent intensity of the Mn²⁺ co-doped (q = 0–0.4) host lattices on the fixed Na⁺ and Eu²⁺ contents was also investigated. Co-doping Na⁺ with Mn²⁺ and Eu²⁺ emitters in the host structure enabled efficient energy transfer from Eu²⁺ to Mn²⁺. The mechanism underlying this energy transfer was also discussed. The Commission Internationale de I’Eclairage (CIE) coordinates near the yellow and red regions of the obtained phosphors were observed. Each of Ba_8.9Eu_0.1Y₂Si₆O₂₄, Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄, and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors with a 405 nm LED chip was fabricated. The color rendering index (CRI, R_a) at correlated color temperature (CCT) with the CIE coordinates was exhibited for the LEDs. The thermal quenching and activation energy for the Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄ and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors were measured.     

Structural stability of ternary D8m–Ti5Sb2X (X=Al,Ga, In,Si, Ge,Sn) compounds

The crystal and electronic structures of Ti₅Sb₂X (X=Al, Ga, In, Si, Ge, Sn) ternary compounds in the Nb₅Sn₂Si-type structure (ternary-D8_m) have been investigated by means of first principles calculations. The calculated structural parameters are in good agreement with the experimental data. The total electronic densities of states as well as the Bader charges of the atoms have been computed. Both electronic and size effects allow to explain the stability of the Ti₅Sb₂X (X=Al, Ga, In, Si, Ge, Sn) ternary compounds in the ternary D8_m structure. The enthalpies of formation of the ternary D8_m compounds have been obtained. The off-stoichiometry domains of D8_m–Ti₅Sb₂Ga and D8_m–Ti₅Sb₂Si are discussed.     

Thermodynamic optimizations of the Nd-Sn and Sn-Tb systems

The thermodynamic optimizations of the Nd-Sn and Sn-Tb binary systems were carried out by means of the Calculation of Phase Diagram (CALPHAD) method on the basis of the available experimental data including the thermodynamic properties and phase equilibria. The Gibbs free energies of the liquid, bcc, bct, dhcp and hcp phases were described by the substitutional solution model with the Redlich-Kister equation, while all of the intermetallic compounds (Nd₅Sn₃, Nd₅Sn₄, Nd₁₁Sn₁₀, NdSn, Nd₃Sn₅, NdSn₂, Nd₃Sn₇, Nd₂Sn₅, NdSn_3, Sn₃Tb, βSn₇Tb₃, αSn₇Tb₃, Sn₂Tb, Sn₅Tb₄, SnTb₄, Sn₁₀Tb₁₁, Sn₄Tb₅ and Sn₃Tb₅) were described by the sublattice model. A set of self-consistent thermodynamic parameters of each phase in the Nd-Sn and Sn-Tb binary systems has been obtained, and the calculated results are in good agreement with the available experimental data.     

Critical evaluation and thermodynamic assessment of the R2O–P2O5 (R = Li,Na and K) systems

The R₂O–P₂O₅ (R = Li, Na and K) systems are thermodynamically optimized based on the evaluated phase equilibria and thermodynamic data by the CALPHAD method. Liquid phase is described by the Modified Quasichemical Model, which takes short-range ordering in liquid solution into account. All intermediate phases RPO₃, R₅P₃O₁₀, R₄P₂O₇ and R₃PO₄ are treated as stoichiometric compounds and the corresponding polymorphic transitions are considered. A set of self-consistent model parameters for describing the Gibbs free energy of each phase are obtained. The experimental phase equilibria, enthalpy of formation, entropy, heat capacity and activity are reproduced well within experimental error limits. The calculated liquidus around compounds become flatter with the increase of P₂O₅ content, suggesting that the degree of stability of phosphate increases as its composition approaches R₃PO₄. The calculated enthalpies of formation for intermediate compounds become more negative and entropies become more positive with the increase of atomic numbers of alkali metals.     

Solution of the stochastic H ∞-optimization problem for discrete time linear systems under parametric uncertainty

The stochastic H _∞-optimization problem for a linear discrete time system with uncertain parameters is formulated and solved. The system operates in the presence of Gaussian random disturbances. The original problem with parametric uncertainty is reduced to the stochastic H _∞-optimization problem without uncertainty and having one extra input, which is essentially the mixed H ₂/H _∞-optimization problem. In a sense, the problem considered in this paper incorporates the classical H ₂/H _∞-and H _∞-optimization problems as limiting cases.