Optical spectroscopy of europium nitrate with 2,2′-bipyridine Eu(NO3)3·Bpy3. One more of compounds with outer-sphere Bpy molecule?

The complex compound Eu(NO₃)₃·Bpy₃ (Bpy, 2,2′-bipyridine) was synthesised and analysed by methods of optical spectroscopy. The spectra and details of the structure were discussed and compared with ones of well-known compounds Eu(NO₃)₃·Bpy₂ and Eu(NO₃)₃·Phen₂ (Phen, 1,10-phenanthroline). The water admixed to the ethanol as solvent promotes Bpy building into the outer sphere of complex [Eu(NO₃)₃·Bpy₂]·Bpy. Both kinds of Bpy molecules in Eu(NO₃)₃·Bpy₃ compound are nearer to coplanar, than Bpy in Eu(NO₃)₃·Bpy₂. The bonds Eu–N are stronger and the bonds Eu–O are weaker in Eu(NO₃)₃·Bpy₃ in comparison with the ones in Eu(NO₃)₃·Bpy₂. The outer-sphere Bpy molecule, effecting as a “steric” factor, changes the nearest surroundings of Eu³⁺ ion in [Eu(NO₃)₃·Bpy₂]·Bpy, making it similar to one of Eu(NO₃)₃·Phen₂.     

Electrical properties of magnesium sodium hydrogen monophosphate: MgNa3H(PO4)2

Magnesium sodium hydrogen monophosphate, Na₃MgH(PO₄)₂, crystallizes in the triclinic cell . The crystal morphology is related to the synthesis temperature and the evaporation rate. Samples were characterized through X-ray diffraction and chemical analysis, examined by IR and Raman vibrational spectroscopy and impedance and modulus spectroscopy techniques. The conductivity relaxation parameters associated with some H^· conduction have been determined from an analysis of the M^″/M_max^″ spectrum measured in a wide temperature range. Transport properties in this material appear to be due to an H^· ion hopping mechanism.     

(Gd0.8Ca0.2)2Ce2O6.6陶瓷的制备及热导率

以Gd2O3、CeO2和CaO为原料,采用固相反应法制备(Gd0.8Ca0.2)2Ce2O6.6陶瓷材料。用X射线衍射(XRD)技术和扫描电镜(SEM)研究样品的相组成和微观组织,用激光脉冲法测试样品的热扩散系数。结果表明,所制备的样品具有单一的萤石结构,组织致密且晶界清晰,其在800℃的热导率仅为YSZ陶瓷的89%,较低热导率表明该材料有潜力用作新型热障涂层用陶瓷材料。     

IR and Raman spectra of poled and unpoled LiNbO3 single crystals

LiNbO₃ single crystals were grown by the Czochralski technique in an air atmosphere. The polarized IR and Raman spectra of both poled and unpoled LiNbO₃ single crystals were measured and compared. The spectra were recorded at different temperatures between 20 and 300 K. In addition, we discussed the phonon anomalies and anharmonicity in both, IR and Raman spectra.     

Raman scattering study of the lattice dynamics of β-Zn4−xCdxSb3

Micro-Raman scattering experiments have been performed on the ternary solid solution in the Zn₄Sb₃–Cd₄Sb₃ system. Ten samples were studied; their compositions go from Zn₄Sb₃ to Zn_3.1Cd_0.9Sb₃. The homogeneity of these samples was checked by X-ray diffraction and electron microprobe analysis. The corresponding lattice parameters were calculated and their concentration dependence exhibits a small negative deviation from Vegard's law between end members of the Zn₄Sb₃–Cd₄Sb₃ system.

Three peaks and one shoulder are easily observable in the Raman spectrum of β-Zn₄Sb₃. These peaks are still present when the zinc atoms are substituted by cadmium ones. As the intensities of the Raman lines were observed to be very sensitive to the direction of the microcrystallites, only the change of the position could be discussed. From these experiments, we can suggest that the peak at about 155 cm⁻¹ should imply essentially Sb–Sb bondings while the peaks at about 172 cm⁻¹ and 320 cm⁻¹ must also imply Cd–Sb and Zn–Sb bondings.     

电渣重熔中TiO2对低氟CaF2-CaO-Al2O3-MgO-Li2O渣黏度和结构的影响

本文研究了连续冷却条件下电渣重熔中TiO₂对低氟CaF₂-CaO-Al₂O₃-MgO-Li₂O渣黏度的影响,并利用傅里叶变换红外光谱和拉曼光谱分析水淬渣和对应结构的关系。结果表明,渣的黏度随着TiO₂的增加而降低,当TiO₂含量达到13.1%,随着温度从1743K, 1793K, 1843K 增加至1893K时, 对应黏度从0.067 Pa?s, 0.059 Pa?s, 0.056 Pa?s 降低到0.054 Pa?s;当温度达到1843K或之上时,TiO₂的加入对降低黏度有较小的影响。随着TiO₂含量从0,4.3%,8.7%增加至13.1%,黏流活化能从58.0 kJ/mol,47.7 kJ/mol,42.8 kJ/mol降低到38.6 kJ/mol。此外,红外光谱结果表明,随着TiO₂的加入,渣中[AlOnF_4-n]-四面体络合物和[AlO₄]-四面体网状结构被解聚,但[AlO₆]-八面体结构没有发现;同时,拉曼光谱分析表明,TiO₂加入可解聚[AlO₄]-四面体网状结构中Al-O-Al键, 并且Q^₄单元转化为Q^₂单元,同时形成O-Ti-O和Ti-O-Ti键。这些结果都表明TiO₂可降低渣的聚合度,并且有利于渣的结构简单化。最终,黏度变化与渣的对应结构有很好的一致性。     

Effect of holmium additions on microstructure in YBa2Cu3O7−δ

The microstructure of Y–Ho–Ba–Cu–O samples with two different levels of Ho, Ho/Y = 0.5 and 1.0, processed by the trifluoroacetate metalorganic deposition process, have been studied by transmission electron microscopy (TEM) techniques, including high-resolution TEM, conventional TEM and fine-probe energy-dispersive spectroscopy. Oxide nanoparticles with varying levels of Ho have been characterized in detail, and related to other microstructural features. At a lower level of Ho, the (1 1 0) coarse twins with the boundary spacing of 30–60 nm form. Further increase in Ho content considerably produces fine microtwins, and increases the density of nanoparticles and microtwins. Ho additions increase the critical current for the magnetic field parallel to the c-axis, and decrease it for the field parallel to the a–b plane, resulting in a decreased anisotropy of critical current with field angle compared with undoped Y–Ba–Cu–O samples processed under similar conditions. These trends are discussed in terms of the detailed microstructural observations.     

Ionic conductivity and Raman investigations on the phase transformations of Na4P2O7

The ionic conductivity and thermo-Raman spectra of anhydrous sodium pyrophosphate Na₄P₂O₇ were measured dynamically in the temperature range from 25 to 600 °C with a heating rate of 2 °C min⁻¹ to understand the structural evolution and phase transformation involved. The DSC thermogram was also measured in the same thermal process for the phase transformation investigation. The spectral variations observed in the thermo-Raman investigation indicated the transformation of Na₄P₂O₇ from low temperature phase () to high temperature phase () proceeded through pre-transitional region from 75 to 410 °C before the major orientational disorder at 420 °C and minor structural modifications at 511, 540 and 560 °C. The activation energies and enthalpies of the proposed phase transformations were determined. The possible mechanism for temperature dependent conductivity in Na₄P₂O₇ was discussed with the available data.     

Microstructure and properties of CVD γ-Al2O3 coatings

This work deals with the microstructures and wear properties of chemical vapour deposited γ-Al₂O₃. The γ-Al₂O₃ coatings were deposited at 800 °C on TiN and Ti(C,N) pre-coated cemented carbide substrates. The microstructures developed in the γ-Al₂O₃ coatings and the influence of the nucleation surface on the growth of γ-Al₂O₃ were characterised using transmission electron microscopy, electron energy-loss spectroscopy and X-ray diffraction. The γ-Al₂O₃ coatings were fine-grained with a high density of {1 1 1} growth twins and contained some residual sulphur. γ-Al₂O₃ was found to grow epitaxially on the investigated substrates. The mechanical properties were evaluated in metal cutting and were compared with those of κ-Al₂O₃ coated tools. As compared with the κ-Al₂O₃ coatings, the γ-Al₂O₃ coatings exhibited slightly worse adhesion and tendency for edge chipping. However, the γ-Al₂O₃ coatings showed better crater wear resistance on the rake face than κ-Al₂O₃ coatings.     

Induced crystallization and physical properties of Li2O–CaF2–P2O5:TiO2 glass system: Part I. Characterization, spectroscopic and elastic properties

Li₂O–CaF₂–P₂O₅ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 0.8 mol%) were crystallized at 500 °C. The samples are characterized by X-ray diffraction, scanning electron microscopy and differential thermal analysis techniques. Spectroscopic properties (IR and Raman) and elastic properties (viz., Young's modulus E, shear modulus G and micro-hardness H) at room temperature are studied. The X-ray diffraction and the scanning electron microscopic studies revealed the presence of lithium phosphate, lithium titanium phosphate and titanium phosphate crystal phases. The differential thermal analysis traces of these samples exhibit three crystalline temperatures. The IR and Raman spectra of these samples have exhibited bands due to TiO₄ and TiO₆ structural units in addition to the conventional bands due to various phosphate structural groups. The analysis of these results indicated that the sample crystallized with 0.6 mol% of TiO₂ possesses the highest density, high mechanical strength and more compact network.     

Thermodynamic properties and phase diagrams of the binary systems B2O3–Ga2O3, B2O3–Al2O3 and B2O3–In2O3

We calculated the binary phase diagrams B₂O₃–Ga₂O₃, B₂O₃–In₂O₃ and B₂O₃–Al₂O₃, and the Gibbs energy of formation of the binary compounds, using experimental liquidus data. The B₂O₃–Ga₂O₃ system is of industrial importance, because liquid B₂O₃, in which Ga₂O₃ is not very soluble, is used to protect GaAs during growth of single crystals of GaAs. During recovery of noble metals B₂O₃ is added to slags containing Al₂O₃ to lower the melting point and the viscosity. The B₂O₃–In₂O₃ system is of much less importance to industry. In all three systems we have a liquid miscibility gap, and also solid binary compounds, none of which melt congruently. The miscibility gaps are not surprising, because even in the B₂O₃–Bi₂O₃ system where four congruently melting compounds are present, a liquid miscibility gap exists close to B₂O₃.     

Synthesis of crystalline γ-Al2O3 with high purity

Crystalline γ-AlO(OH) was synthesized by the precipitation of sodium aluminate and oxalic acids in aqueous solution. And then γ-AlO(OH) was successfully transferred to γ-Al₂O₃ after subsequent high temperature heat treatment. The effects of reaction conditions on formation of γ-AlO(OH) and γ-Al₂O₃ were further investigated in detail. The XRD analysis shows that the complete formation of crystalline γ-Al₂O₃ is at pH 8–9, reaction temperature of 93–96 °C and calcination temperature of higher than 400 °C. The product of γ-Al₂O₃ contains impurity, including iron, calcium and silicon ion with a low content of about 0.01% and has large specific surface area and high pore volume of 269.9 m²/g and 0.57 mL/g, which can be applied in catalysts and catalyst supports.     

Formation and properties of BaxFe3−xO4 with spinel structure by mechanochemical reaction of α-Fe2O3 and BaCO3

Magnetic Ba_xFe_3−xO₄ (x  0.23) with spinel structure was fabricated by ball milling of mixture of BaCO₃ and nonmagnetic α-Fe₂O₃ powders, and the molar ratio of BaCO₃ and α-Fe₂O₃ is 1:6. In the milling process, a mechanochemical reaction took place between BaCO₃ and α-Fe₂O₃, and Ba cation incorporated into α-Fe₂O₃ with rhombohedral structure to form a α-(Fe,Ba)₂O₃ solid solution. The Ba content in the α-(Fe,Ba)₂O₃ increased with increasing milling time, when the Ba content exceeded a limited solubility, the α-(Fe,Ba)₂O₃ transformed into a phase of Ba_xFe_3−xO₄ with spinel structure, where the Ba cation occupied an octahedral site or tetrahedral site. The product obtained in the balling process was different from that prepared in the annealing process at atmospheric pressure, which was BaFe₂O₄ with orthorhombic structure. Accompanying the crystal structure transition from α-(Fe,Ba)₂O₃ to Ba_xFe_3−xO₄, the magnetic properties also changed from nonmagnetism into ferromagnetism. The saturation magnetization was 53.3 emu/g and coercivity was 113.7 Oe. The mechanism of transitions of the crystal structure was discussed in the present work.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Phase transitions in Cd3P2 at high pressures and high temperatures

The high-pressure, high-temperature structural behaviour of Cd₃P₂ has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0 GPa in compression. The experimental zero-pressure bulk modulus of the low-pressure phase is 64.7(7) GPa, which agrees quite well with the calculated value of 66.3 GPa using the tight-binding linear muffin-tin orbital method within the local density approximation. Tentatively, the high-pressure phase has an orthorhombic crystal structure with space group Pmmn (#59). The relative volume change at the phase transition is ΔV/V = −5.5%. Amorphization of the sample occurs above 25 GPa. A P–T phase diagram of Cd₃P₂ has been constructed. A metastable phase is observed at ambient conditions after heating the sample to above 600 K at about 3 GPa. A hexagonal unit cell can describe the crystal structure of the metastable phase.     

Processing and properties of ZrO2(3Y2O3)–Al2O3 nanocomposites

Nanocomposites of yttria-stabilized zirconia (YSZ), containing 20 and 40 wt% alumina, were prepared by a two-step process: (1) fine-particle aggregates of the constituent phases were melted and homogenized in a high enthalpy plasma, prior to rapid quenching in water to obtain metastable starting powders, and (2) the metastable powders were consolidated by hot isostatic pressing (HIP), under conditions designed to ensure the formation of nanocomposites by controlling the metastable-to-stable phase transformation during sintering. In both cases, the resulting nanocomposites had completely uniform structures, comprising 27 and 50 vol% of -Al₂O₃ in a tetragonal YSZ matrix phase. Measurements of hardness and indentation toughness were correlated with observed structures.     

TiN/Cr/Al2O3 and TiN/Al2O3 hybrid coatings structure features and properties resulting from combined treatment

New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al₂O₃ coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H₂SO₄, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al₂O₃ sub-layers mixing).     

La0.9Sr0.1Ga0.8Mg0.2O3−δ sintered by spark plasma sintering (SPS) for intermediate temperature SOFC electrolyte

The La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) powders for intermediate temperature SOFC electrolyte have been synthesized by glycine-nitrate combustion process. The as-synthesized powders show almost pure perovskite phase. And then, the as-synthesized powders were sintered by SPS at 1300 °C to prepare electrolyte. The SEM, XRD and AC impedance were employed to characterize the microstructure, phase and electrical conductivities. Results show that the grain size is very fine, less than 1 μm, and the relative density of the pellet after sintering by SPS is about 94.7%. There is very little amount of secondary phases after SPS and the grain boundary and secondary phase resistance is very small. The electrolyte sintered by SPS shows higher conductivities than that sintered by conventional method at the same temperature. The activation energy at lower temperatures (400–700 °C) and higher temperatures (700–800 °C) is about 0.94 and 0.49 eV, respectively. Spark plasma sintering is a promising and effective method to sinter the LSGM electrolyte.     

Spectral properties of the TCNQ anion radical salt (N-Me-2,5-(Me)2-Pz)(TCNQ)2

We present the optical conductivity, infrared- and Raman-active charge sensitive phonon modes of the new 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) anion radical salt containing N-methyl-2,5-dimethyl-pirazinium cations (N-Me-2,5-(Me)₂-Pz)⁺. Comparison of the calculated frequencies of the totally symmetric TCNQ modes with corresponding vibrations in the (N-Me-2,5-(Me)₂-Pz)(TCNQ)₂ salt is given. An attribution of the main bands observed in the spectra of the salt is offered and discussed. The charges estimation with both, structural and spectroscopic methods is in good agreement with each other and confirms almost full charge transfer from cation to TCNQ species.