Change of the Prenematic Order in the Isotropic Phase Close to the Isotropic–Nematic Phase Transition with Increasing Aerosil Nanoparticles Density

The influence of the hydrophilic and hydrophobic aerosil nanoparticles density on the formation of the prenematic order close to the isotropic – nematic (I–N) phase transition is presented. The lowering of the activation energy, with the increase of aerosil nanoparticles density, suggests a change of the prenematic order in the isotropic phase. The temperature dependence of the static dielectric permittivity for 4–n–pentyl–4′–cyanobiphenyl (5CB) exhibits an anomaly near the I–N phase transition. With the increase of aerosil density, a substantial modification in the anomaly of the static permittivity was observed in the isotropic phase. Indicated changes are different for hydrophilic and hydrophobic aerosil as a result of different surface interaction between nematic molecules and aerosil nanoparticles.     

Study on the Local Structure Phase Transition, Spectral Fine Structure and EPR Spectra of RbCdF3∶Ni2+ Crystals

本文采用半自洽场(semi-SCF) 3d轨道模型和μ-K-α模型,利用完全对角化方法,建立了Oh、D4h对称晶体场局部结构参数与光谱精细结构、EPR谱之间的定量关系,统一解释了RbCdF3∶ Ni2晶体的光谱精细结构和EPR谱.所得理论结果与实验值符合很好.     

Synthesis and Crystal Structure of Pivalamidate-Bridged Trinuclear Platinum–Copper Complex with a Linear Pt–Cu–Pt Core

Abstract The heterotrimetallic complex [Cu{trans-Pt(NH₃)₂(NHCO^tBu)₂}₂](NO₃)₂ was synthesized and structurally characterized by X-ray crystallography. The cationic complex consists two trans-[Pt(NH₃)₂(NHCO^tBu)₂] units and one Cu²⁺ ion, which are linearly held together by four bridging pivalamidate ligands. The compound crystallizes in the monoclinic space group P2₁/c with a = 13.18(1) ?, b = 13.12(1) ?, c = 21.38(2) ?, β = 116.88(3)°?, V = 3674(5) ?³, and Z = 4. The trimeric Pt–Cu–Pt cation further aggregates into a dimer of trimer via a weak Pt···Pt interaction. Graphical abstract Synthesis and crystal structure of pivalamidate-bridged trinuclear platinum–copper complex with a linear Pt–Cu–Pt core Chao Chen, Huayu Qiu*, Fenghui Liu and Wanzhi Chen* A heterotrimetallic complex [Cu{trans-Pt(NH3)₂(NHCO^tBu)₂}₂](NO₃)₂ was synthesized and structurally characterized by X-ray crystallography.      

The Effect of Vanadium on Morphology and Chemical Composition of Carbides in High Alloyed Chromium–Molybdenum Steels

Despite of the permanent progress of technique and finding of the new, modern materials that successfully replace metals, steel continues to play an important role in the technical practice. The tendency is to discover the new alloys with better mechanical and technological characteristics, compared to conventional and standard types of steels. High-alloyed Cr–Mo steel, with a high content of Vanadium is the new type of wear resistant material, with high hardness and satisfactory impact and fracture toughness. During the solidification process Vanadium, as a strong carbide forming element, creates a network of M₇C₃ type carbide grains around the metal matrix, while in the matrix, the finely dispersed V₆C₅ type carbides are formed. In this paper, the chemical composition and morphology have been studied of carbides and the other phases present in the metal matrix in 1.4 wt % C, 12 wt % Cr, 1.0 wt % Mo steels with additions up to 3.0 wt % V. Experimental results indicate that Vanadium affects the solidification process in high Chromium steel. Vanadium is distributed between eutectic M₇C₃ carbide and the matrix, but its content in carbides is considerably higher. Vanadium changed the microstructure parameters of phases present in the structure of alloys, including volume fraction, size and morphology.     

Studies on binary silicate glasses based on the SiKα and SiKß emission X-rays

The SiKα and Kβ X-ray emission spectra of binary silicate glasses of the Li₂O–SiO₂, Na₂O–SiO₂, K₂O–SiO₂, Cs₂O–SiO₂, B₂O₃–SiO₂, and GeO₂–SiO₂ systems were measured with an X-ray fluorescence spectrometer to examine the chemical effects on the spectra. The SiKα peak wavelengths for all the glasses agreed with that for SiO₂ glass, which corresponded to the concept that the coordination number of Si shouldbe four in all the glasses examined in this study. The SiKβ peak wavelength decreased with increasing alkali content in the alkali silicate glasses, indicating that the Si–O bond weakend in average as the alkali oxide was added to SiO₂ glass. On the other hand, no drastic shift in the SiKβ peak wavelength was observed in the B₂O₃–SiO₂ and GeO₂–SiO₂ systems, and this was interpreted as showing the constancy of Si–O bond strength in these glasses.     

Studies on conventional and Sankaranarayanan–Ramasamy (SR) method grown ferroelectric glycine phosphite (GPI) single crystals

Transparent single crystals of glycine phosphite were grown by Sankaranarayanan–Ramasamy (SR) method and conventional slow evaporation solution technique (SEST) which had the sizes of 100 mm in length, 30 mm diameter and 10×11×8 mm³. The conventional slow evaporation and Sankaranarayanan–Ramasamy method grown glycine phosphite single crystals were characterized using laser damage threshold, chemical etching, Vickers microhardness, UV–vis–NIR and dielectric analysis. The laser damage threshold value was higher in SR method grown GPI crystal as against conventional method grown crystal. The SR method grown GPI has higher hardness and also higher transmittance compared to conventional method grown crystal. The chemical etching and dielectric loss measurements indicate that the crystal grown by SR method has low density of defects and low value of dielectric loss compared to conventional method grown GPI crystal.     

A Comparison of the High Resoluton Crystal Structures of the π- Molecuar Complexes of Anthracene and Phenothiazine with Pyromellitic Dianhydride

The π-molecular complexes formed by aromatic molecules with three rings tend to form crystals of high purity and are therefore ideal for solid state spectroscopic and photocurrent studies. We have therefore undertaken an investigation of the detailed structures of a number of such complexes in order to facilitate the interpretation of such data and other physical properties and in order to better understand the large changes in physical properties generated by small changes in composition and molecular packing. The piezoreflection spectra of the anthracene-pyromellitic dianhydride complex (A-PMDA) has been studied by Eckhardt and Merski (1973). The photo-current excitation spectra of A-PMDA was reported by Karl and Ziegler (1975) and more recently the preparation, optical properties, absorption and photoconductivity properties of phenothiazine-pyromellitic dianhydride have also been studied. (Anthonj, Karl, Robertson and Stezowski, 1979).     

Nanophase separation and effects on properties of Ge–As–Se chalcogenide glasses

Nanophase separation in the bulk Ge–As–Se chalcogenide glasses was observed by SEM and supported by XRD and IR measurements. Effects of nanophase separation on glass transition temperature (T_g), microhardness (H_v), optical band gap (E_opt) and thermal expansion coefficient (α) were investigated in terms of glass rigidity transitions. According to the correlations between the properties and average coordination number Z, it is established that nanophase separation becomes more intensive when Z is larger than 2.64.     

Temperature and Pressure Dependence Studies of the Motions of the +NH3 Radical Trapped in γ Irradiated Ammonium Perchlorate Single Crystal

The temperature and pressure dependences of the ⁺NH₃ coupling tensors have been investigated by ESR spectroscopy. The linear variation of the reduced correlation time of the “rotational diffusion” motion with reciprocal of the temperature is shown to be unrelated to the dilatation of the matrix. Comparison with ⁺ND₃ results gives the contribution to the nitrogen isotropic coupling constant of the out of plane vibration of the nitrogen atom.     

Application of Empirical Si–O–C Potential to Simulate Amorphous Atomic Structures and Transition Layers by the Bond Switching Method

Crystallography Reports - The parameters of REBO2 empirical potential for the Si–O–C system are presented. The results of the calculations using this potential agree well with the...     

FTIR and UV–VIS spectroscopy investigations on the structure of the europium–lead–tellurate glasses

Glasses in the xEu₂O₃·(100-x)[4TeO₂·PbO₂] system where 0 ≤ x ≤ 50 mol% have been prepared using the melt quenching method. The influence of europium ions on the structure of lead–tellurate glasses has been investigated using density measurements, FTIR and UV–VIS spectroscopy. Structural changes produced by increasing the rare earth concentration were followed.The europium and lead ions show a preference towards [TeO₃] structural units causing a deformation of the TeOTe linkages. Structural changes inferred by analyzing the band shapes of IR spectra revealed that the increase of the Eu^+ 3 content causes the intercalation of [EuO_n] entities in the [TeO₄] chain network. The excess of oxygen can be supported into the glass network by the formation of [PbO_n] and [EuO_n] structural units.The UV–VIS spectroscopy data show that europium ions enter the glass matrix in the Eu²⁺ and Eu³⁺ valence states, the last being predominant in the studied glasses. The Pb^+ 2 ions produce strong absorption in the ultraviolet domain.     

Spectroscopic studies on vitreous and polycrystalline heavy metal gallium–bismuthates

Local order changes determined by Fe₂O₃ (0–20 mol%) addition to Bi₂O₃–Ga₂O₃ matrix in glass and vitroceramic samples were investigated by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and Fourier transform infrared (FTIR) spectroscopies. Glass samples were prepared using the melt-quench technique. The vitroceramic samples were obtained by crystallization, as a result of the heat treatment applied on glass samples. The glass network mainly consists of [BiO₆] octahedral units. After heat treatment induced crystallization, [BiO₃] pyramidal units are predominant in samples. As evidenced by electron spin resonance, the Fe³⁺ ions surrounding is characterized by low crystal fields, excepting the vitreous sample with the lowest Fe₂O₃ content, wherein the Fe³⁺ ions occupy sites of low symmetry, characterized by high crystal fields.     

Effect of Mo–Fe substitution on glass forming ability and thermal stability of Fe–C–B–Mo–Cr–W bulk amorphous alloys

Amorphous Fe_67?xC₁₀B₉Mo_7+xCr₄W₃ (x = 1–7 at.%) plates with 0.64 mm thickness were prepared by copper mold casting. The thermal properties and microstructural development during heat treatments were investigated by a combination of differential scanning calorimetry, differential thermal analysis, and X-ray diffraction. The glass forming ability (GFA) and activation energy for crystallization have a distinct dependence on Mo content. Fe₆₂C₁₀B₉Mo₁₂Cr₄W₃ was the best glass former in this study, demonstrating a supercooled liquid region, ΔT_x = 51 K, and an activation energy for crystallization, Q = 453 kJ/mol. The GFA of alloys in this system was governed by elastic strain optimization resulting directly from the variation in Mo content. Heat treatments were performed to demonstrate resistance to crystallization under typical processing conditions. Alloys in this system exhibited a three phased evolution during crystallization. A second set of heat treatments was performed to identify each phase. An analysis of phase evolution revealed a distinct dependence of phase evolution with stepwise substitution of Mo for Fe in this system.     

The effect of composition and temperature on the amount and type of nanoferrite particles inserted in Fe2O3–ZnO–MgO–SiO2 glass–ceramics

Glass–ceramics with the composition 2Fe₂O₃.1ZnO.1MgO.96SiO₂ [4ZnMgFe] and 2Fe₂O₃.2ZnO.3MgO.93SiO₂ [7ZnMgFe] (mol%) were prepared using the sol–gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron diffraction (ED) and Mössbauer spectroscopy (MS) were used to investigate the glass–ceramics structure. The samples contain ferrite nanoparticles embedded in a glass matrix. However, zinc ferrite nanoparticles seems to be the preferential crystalline phase formed. The amount of ferrite particles depends on treatment temperature and sample composition. The Mössbauer spectroscopy measurements show that ferrite nanoparticles can exhibit a ferrimagnetic behaviour combined with superparamagnetism.     

Spectroscopic properties and ab initio calculations on the structure of erbium–zinc-borate glasses and glass ceramics

Glasses in the (Er₂O₃)_x·(B₂O₃)_(60 ? x)·(ZnO)₄₀ system (0 ≤ x ≤ 15 mol%) have been prepared by the melt quenching technique. X-ray diffraction, FTIR spectroscopy, UV-VIS spectroscopy and ab initio calculations studies have been employed to study the role of Er₂O₃ content on the structure of the investigated glass system.X-ray diffraction and infrared spectra of the glasses reveal that the B–O–B bonds may be broken with the creation of new non-bridging oxygen ions facilitating the formation of Er–O–B linkages. The excess of oxygen can be accommodated in the network by the conversion of sp² planar [BO₃] units to the more stable sp³ [BO₄] tetrahedral structural units. The linkages of the [BO₄] structural units can polymerize in [B₃O₉]^? 9 cyclic trimeric ions which will produce the ErBO₃ crystalline phase. An increase of the efficiency corresponding to the ⁴I_15/2 state to ⁴I_11/2 state (4f–4f) transitions of Er^+ 3 ions was observed for the erbium oxide richest glasses.Ab initio calculations on the structure of the matrix network show the thermodynamic instability of the [BO₄], [ZnO₄] and [Zn₄O] structural units. Formation of three-coordination oxygens was necessary to compensate shortage of oxygens from zinc ions.     

Effect of germanium on the microstructure and the magnetic properties of Fe–B–Si amorphous alloys

In this work, we present a systematic study on the crystallization kinetics and the magnetic properties of melt-spun Fe₈₀B₁₀Si_10 ? xGe_x (x = 0.0 ? 10.0) amorphous alloys. The activation energy for crystallization, determined by differential scanning calorimetry, displayed a strong dependence on the Ge content, reflecting a deleterious effect on the alloys' thermal stability and their glass forming ability with increasing Ge concentration. On the other hand, the alloys exhibited excellent soft magnetic properties, i.e., high saturation magnetization values (around 1.60 T), alongside Curie temperatures of up to 600 K. Complementary, for increasing Ge substitution, the ferromagnetic resonance spectra showed a microstructural evolution comprising at least two different magnetic phases corresponding to a majority amorphous matrix and to Fe(Si, Ge) nanocrystallites for x ≥ 7.5.     

Dependences of the crystallization behavior of Al–Ni–La amorphous alloys on La and Ni contents

Crystallization behaviors of Al–Ni–La amorphous alloys with a fixed Ni (La) content of 6 at.% were investigated by X-ray diffraction and differential scanning calorimeter when the La (Ni) content changes from 3 to 9 at.%. The results show that the thermal stability of the amorphous alloys monotonically increases with increasing the La (Ni) content. Glass transition only exists in the alloys with the La (Ni) content higher than 6 at.%. La plays a more significant role than Ni in promoting the glass-forming ability, improving the thermal stability, stabilizing the supercooled liquid region, depressing the precipitation of fcc-Al in the first crystallization process and increasing the apparent activation energy of the first reaction.