Solid Solutions of Rare-Earth Cuprates and Their Electrical Properties

Mixed cuprates based on La–Sm, La–Gd, Pr–Y, Pr–Nd, and Sm–Gd oxides are synthesized, and their physicochemical properties are investigated. The electrical properties of the studied cuprates are interpreted within the model of oxidation–reduction reactions.     

Magnetic Properties of Ilmenite-Hematite Solid Solutions

The magnetic and dielectric properties of some ilmenite-hematite solid solutions are reported. These properties resemble those of the ferrites. Compositions possessing high electrical resistivities and low dielectric losses were prepared. The introduction of manganese into the system (1 - x)Ni_1-vMn_vTiO₃+ xFe₂O₃ increases the room temperature magnetic moments and decreases the resistivities.     

Composition and Properties of Hot-Pressed SiC-AIN Solid Solutions

High-density SiC-AIN compositions were fabricated from powder mixtures by hot-pressing in the 1700° to 2300°C temperature range. At 2100°C, a 2H solid solution was found from =35 to 100 wt% AlN. The single-phase solid solution samples had steep composition gradients of >10%/μm within the grains. Lattice parameters closely followed Vegard's law. For compositions with <35% AIN, multiphase assemblages were found. Increasing grain size was observed for increasing firing temperature for SiC and AIN. Grain size of the solid solutions was significantly smaller than for SiC or AIN fired to the same temperature. Microhardness values decreased linearly in the solid solution region with increasing AIN content. Flexural strengths of SiC and AIN decreased with increasing firing temperature and increasing grain size. The strengths of SiC, AIN, and the solid solutions were low for materials hot-pressed at 2100°C.     

Thermodynamic and Structural Properties of Sodium Lithium Niobate Solid Solutions

Thermodynamics of the Na_1−xLi _x NbO₃ system is investigated by high-temperature drop-solution calorimetry in molten 3Na₂O–4MoO₃ solvent at 973 K. Standard molar enthalpies of formation are derived. The estimated heats of transition between hypothetical and stable structures, lithium niobate and perovskite for NaNbO₃ and vice versa for LiNbO₃ are −6 kJ/mol and −10 kJ/mol, respectively. X-ray diffraction studies at room temperature showed for 0 ≤ x ≤ 0.14 there are three phases based on different ordering of the perovskite type lattice: orthorhombic with a quadrupled reduced perovskite cell at 0 ≤ x ≤ 0.02, orthorhombic with a doubled reduced perovskite cell at 0.015 ≤ x ≤ 0.14, and rhombohedral at 0.08 ≤ x ≤ 0.13. There are two two-phase (morphotropic) regions with coexistence of the two orthorhombic phases at 0.015 ≤ x ≤ 0.02 and with the second orthorhombic phase coexisting with the rhombohedral phase at 0.08 ≤ x ≤ 0.13. A reproducible anomaly in specific heat at ∼600 K, not reported previously, has been observed in pure NaNbO₃. Heat-capacity measurements confirm a phase transition at 553 K for 0.07 ≤ x ≤ 0.09. With increasing lithium concentration, a gradual disappearance of high-temperature phase transitions associated with tilting of oxygen octahedra has been observed.     

Dielectric Properties of Strontium Titanate Solid Solutions Containing Niobia

SrTiO₃ solid solutions containing Sr_0.5NbO₃ were studied by X-ray diffraction and dielectric measurements. Single-phase perovskite solid solutions were formed up to the composition containing 30 mole % Sr_0.5 NbO₃. The addition of niobium resulted in a symmetry change from cubic (SrTiO₃) to tetragonal (solid solution) and the c/a ratio increased with increasing niobium content. The dielectric constant for the solid solutions was lower than that for SrTiO₃. Pronounced dielectric relaxation peaks and dispersion in permittivity were observed for the composition 7SrTiO₃:3Sr_0.5NbO₃. The activation energy for the relaxation process is about 0.42 ev. It is suggested that the existence of the A-site vacancy in the perovskite ABO₃ lattice introduced by the niobium substitution distorts the oxygen octahedra, producing more than one possible "noncentral" site for the Ti⁴⁺ ion. The relaxation arises from the thermal motion over potential barriers separating these alternative sites.     

常减压系统运行过程中存在的问题及解决措施

特针对10MT/a常减压蒸馏装置运行过程中存在的问题进行分析并制定了相应的解决措施。通过这些措施解决常压瓦斯以及减压瓦斯憋压问题,解决了蜡油Ⅰ空气冷却器易结蜡、减压渣油水冷器易结膜等问题,实现了热量利用科学合理,解决了减压凝缩油外排污油利用难的问题,对同类装置安全生产有一定的借鉴性。     

Electrophysical Properties of Oxide Interlanthanides and Solid Solutions Based on Them

The electrophysical properties and nature of oxide interlanthanides LaYO₃, LaYbO₃, LaErO₃, NdLuO₃, LaGdO₃, and GdLuO₃, pure and doped by calcium and hafnium oxides with close ionic radii, are investigated within a temperature interval from 900 to 1600°C and oxygen partial pressure from 2×10⁴ to 1×10^–10 Pa. It is demonstrated that the electric conductivity of the materials considered is determined by nonstoichiometric disordering. The results obtained can be used for synthesis of new types of thermoresistors, oxygen sensors, and other ceramic sensors, as well as various dielectric materials.     

Preparation of Sr1−xCaxLiAl3N4:Eu2+ Solid Solutions and Their Photoluminescence Properties

A series of quaternary nitride solid solutions with a general formula of Sr_1?xCa_xLiAl₃N₄:0.5%Eu²⁺ was synthesized by a solid‐state reaction method. The experimental results showed that a proper amount of Ca‐doping can improve the crystallinity and the photoluminescence properties of the produced phosphors. Rietveld refinement showed that the volume of the unit cell shrank with the increase of Ca substitution for Sr, which resulted in a red shift of the emission spectra from 654 to 665 nm under blue excitation at 475 nm. Rietveld refinement and CASTPE calculations suggested that Ca²⁺ ions prefer to occupy the smaller Sr(I) sites in the crystal lattice, which increases the amount of Eu²⁺ ions in Sr(II) sites and enables the tuning of the chromaticity coordinates of the obtained phosphors. The thermal stability of the produced phosphors is better than that of commercial Sr₂Si₅N₈:Eu²⁺ phosphor. The experimental results qualify the solid‐solution Sr_1?xCa_xLiAl₃N₄:0.5%Eu²⁺ for consideration as a potential candidate for application in white LEDs.     

Properties of Taeniolite/Acriflavine Complex Film Before and After Carbonization: Effect of Acriflavine Content

Taeniolite/acriflavine complexes (TAC) intercalated with various amounts of acriflavine were synthesized. The films derived from these complexes and raw taeniolite (TNL) as a reference were heated (carbonized) below 1273 K under a nitrogen atmosphere, followed by measurements of mechanical properties and electrical resistivity. Compared with TNL film, TAC films, especially with an amount of acriflavine equivalent to the cation exchange capacity of TNL, showed higher thermostability, higher flexibility, lower tensile strength, and larger modulus of toughness. Electrical resistivities of TAC films decreased remarkably after heating to 873 K or higher, in contrast to no change for TNL film. After heating to 1073 K, the electrical resistivities of TAC films clearly decreased with an increase of acriflavine content. This difference disappeared after heating to 1273 K. These behaviors are discussed on the basis of X-ray diffraction, IR spectroscopy. SEM observation, and so on.     

Dielectric Properties of Solid Solutions of Sodium Niobate-Lead Zirconate and Sodium Niobate-Lead Titanate

Solid solutions based on sodium niobate with limited amounts of lead and zirconium or lead and titanium solute ions have been investigated with respect to their dielectric constant versus temperature at 1 kc. per second from −175° to 300°C. Lead zirconate additions to sodium niobate up to 15 mole % cause an increase in dielectric constant, with a value of 1345 at 6°C. being the maximum recorded. Lead titanate additions to sodium niobate cause a general increase in dielectric constant up to 25 mole %, with 675 at 30°C. and 4670 at 154°C. being the maximum values recorded. Polarization versus applied field measurements up to 30,000 volts per cm. show nonreversible polarity for the lead zirconate compositions, whereas the compositions containing from 10 to 50 mole lead titanate are ferroelectric. An induced ferroelectricity phenomenon occurs for the composition containing 5 mole % lead titanate. A remanent polarization of 15 microcoulombs per sq. cm. at a coercive force of 7800 volts per cm. was obtained at room temperature for the composition 0.85 NaNbO₃–0.15 PbTiO₃.     

Microstructure and Mechanical Properties of Heat-Treated Silicon Carbide–Aluminum Nitride Solid Solutions

Nanophase-structured composites were fabricated by heat treating hot-pressed 2H-wurtzite SiC-AlN solid-solution specimens of 25, 50, and 75 mol% AlN within the spinodal decomposition zone. Heat-treatment conditions were 1750°C for 150 h, in flowing nitrogen gas. The hot-pressed specimens contained 2H-wurtzite equiaxed grains, and the grain size increased with AlN content. Lattice parameters followed Vegard's law. Nanoprecipitates with typical modulated tweed-type structures were observed along the [2 1 1 0] zone axis and were orthogonal to the {01 1 2} planes that make angles of 46.70°, 46.90°, and 47.11° to the [0001] for the three compositions. The microhardness, flexural strength, and fracture-toughness values of the heat-treated specimens were not significantly different from the hot-pressed values.     

Solid Solutions in the Keatite Crystal Lattice

The crystallization and stability of keatite solid solutions (ss) of base composition Li₂O·Al₂O₃· n SiO₂ with substitutions of Mg for Li and of B or Ga for Al were studied. Keatite ss with ≥40 mol% Li₂O replaced by MgO and n =3.7 to 5.7 were crystallized. The stability of the phase decreased with increasing MgO and/or SiO₂. An increased degree of imbalance of anion charge, created by the replacement, limited the composition range and stability of this phase. The metastable solid solutions of this composition exsolved cordierite at the higher temperatures. Stable keatite ss with 25 mol% Al₂O₃ replaced by B₂O₃ and n =3 to 5 were also crystallized. When n =3, the lattice accommodated more Li⁺ ions than it could without the replacement. Gallium sesquioxide could substitute exclusively for Al₂O₃ in a stable keatite lattice only for n >4. With n =4, ≥50 mol% Al₂O₃ could be replaced by Ga₂O₃. Glasses with high concentrations of Ga tended to crystallize, in association with predominant keatite ss , phases with Ga in 6-fold coordination. The lattice parameters of the keatite ss did not change appreciably as a result of such substitutions.     

Interdiffusion in CoO-NiO Solid Solutions

Interdiffusion coefficients were measured in CoO-NiO solid solutions over the range 1000° to 1600°C in air and at po₂=5×10⁻⁸ atm. Isothermal values of the interdiffusion coefficients in this system increased exponentially with the CoO concentration. Comparison of the present results with cation-tracer diffusion coefficients for this system measured under similar conditions by Chen and Peterson shows that a Darken-type equation relating the interdiffusion coefficient to the cation-tracer diffusivities is valid for these data.     

Infrared Study of Compounds and Solid Solutions in the System Lithia–Alumina–Silica

The system Li₂O-Al₂O₃-SiO₂ contains several compounds and solid solutions which are important commercially and which are also of interest from a structural point of view. In addition to the interesting polymorphic modifications exhibited by spodumene and eucryptite, the solid solutions between spodumene and eucryptite and more particularly the solid solutions between spodumene and silica (the so-called silica-O series) constitute a group of materials quite suitable for studying the applicability of infrared methods for structural interpretations. The infrared spectra of all the compounds and some typical solid solutions have been obtained and the relations between these spectra and the structures as determined by X-ray methods are discussed.     

Interdiffusion in Semiconducting Oxide Solid Solutions

Previous workers have used the Darken equation to describe Interdiffusion in NiO-CoO. It is shown that, for this equation to be appropriate, not only is a mobile nonionic charge carrier required, but also it is necessary to create cation and anion lattice sites on one side of the couple and destroy them on the other. To achieve this result and conserve oxygen requires transport of oxygen relative to the lattice. It is suggested that oxygen interstitial diffusion provides a likely means of transport with is consistent with the observation that the interdiffusion does not depend on specimen thickness.     

Internal Reactions in Oxide Solid Solutions

Oxidation of wustite-type solid solutions (A, B)0 and reduction of sesquioxide solid solutions (A, B)₂0₃ can lead to the precipitation of a spinel phase (A, B)₃0₄ at an inner reaction front. A representation of the reaction scheme and kinetics for each of the two cases will be given. Observations on the macroscopic morphology of the spinel precipitates and on the structure of the precipitate/matrix interphase boundary are discussed.     

固相法合成孔雀石绿-硼酸复配物及其热变色性能的研究

采用固相法合成了孔雀石绿-硼酸系列可逆热致变色颜料。考察了孔雀石绿和硼酸的配比、无机填料的种类与用量以及环境温度对热变色性能的影响。结果表明：孔雀石绿和硼酸的质量比例在1：(100～400)范围内，颜料在85℃时开始由兰绿色变为黄绿色，加热到110℃时全部变为黄色，冷却时恢复原色，复色时间小于3min；以Al2O3为填料，m(孔雀石绿)：m(硼酸)：m(填料)=1：100：(100～200)，颜料变色敏锐，变色温度降低到75℃，复色时间为小于70s。降低环境温度可以减少复色时间。DSC检测颜料的热变色过程发现70～80℃开始吸热。100～110℃吸热峰达到最大值。     

Structure and Dielectric Properties of BaTiO3–BiYO3 Perovskite Solid Solutions

(1?x)BaTiO₃–xBiYO₃ [(1?x)BT–xBY] polycrystalline ceramics were prepared by solid‐state reaction method. The ceramics are in tetragonal phase when x ≤ 0.04, transform to pseudocubic at x ≥ 0.06, showing a classic ferroelectric to relaxor transition at x = 0.06, where the phase transition temperature was found to shift to higher temperature with increasing frequency. The dielectric permittivity peaks were analyzed by the modified Curie–Weiss law. Both parameters ΔT_diffuse and ΔT_relaxor were found to increase with increasing BY content, demonstrating a stronger relaxor characteristic.