Raman and FTIR studies of phase transitions in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl

The Raman active CC stretching modes and CH₂ deformation modes and the infrared active CN mode are studied as a function of temperature in κ-(BEDT-TTF)₂Cu(N(CN)₂)Cl under pressure. Effects of the structural and superconducting transitions on these excitations are analyzed. The CH₂ and CN modes are sensitive to the thermal expansion around 80 K and to a possible superlattice transition around 160 K while the CC stretching Raman modes ν₂(A_g) are influenced by the formation of the superconducting state.     

MOCVD Ga_xIn_(1-x)As_(1-y)Sb_y Alloys and the Infrared Detector

Ga_xIn_(1-x)As_(1-y)Sb_y alloys have been grown by atmospheric pressure MOCVD on n-GaSb(Te-doped)substrate.The sohd composition was determined by using electron microprobe.The alloys of GalnAsSb withcomposition in miscibility gap were successfully grown.The optical properties of Ga_xIn_(1-x)As_(1-y)Sb_y laverswere characterized by the photoluminescence and the infrared absorption.The spectral responses ofp~+-GaInAsSb/p-Ga_xIn_(1-x)As_(1-y)Sb_y/n-GaSb detectors showed wavelength cut off at 2.4μm and detectivity-D~*=5×10~8 cmHz~(1/2)/W at room temperature.     

Identification of Complex Ions of Nb(V)in FLINAK-O~(2-)System by Infrared Spectra

The FT-IR spectra for K_2NbF_7-FLINAK-O~(2-) solution were measured and compared with the spectraof crystalline K_2NbF_7 and K_2NbOF_6.The results show that the niobium fluoro-complex and/oroxyfluoro-complex ions are presented in these solutions.NbF_7~(2-) complex ion is the predominant species inNb(V)-FLINAK solution(not considering oxide impurity).The influence of O~(2-) on the oxyfluoro-complexions shows that NbOF_6~(3-) as a stable monooxyfluoro-complex anion presented in FLINAK-O~(2-) systemsand the number of NbOF_6~(3-) species are increased with increasing of O~(2-) when molar ratio of O~(2-)/Nb(V)is less than 1.     

Crystal structure and polarized reflectance spectra of α′-(bis(ethylenedithio)-tetrathiafulvalenium)2-bromoiodoaurate, α′-(BEDT-TTF)2IAuBr

A single crystal of α′-(BEDT-TTF)₂IAuBr was synthesized and the crystal structure was determined by X-ray analysis. The structure was found to be isostructural to α′-(BEDT-TTF)₂AuBr₂, having the characteristics of α′-type salts in that the donor molecules are stacked to form a dimerized chain. The electronic structure of α′-type salts was proved to be one-dimensional along the stacking direction from the analysis of the polarized reflectance spectra obtained by use of the microspectroscopic technique.     

Infrared spectroscopic and magnetic behaviour of xNd2O3(1−x)Na2B4O7 glasses

Glasses of the xNd₂O₃^·(1−x)Na₂B₄O₇ system with 0=x=0.25 were studied by IR spectroscopy, density and magnetic susceptibility measurements. IR and density measurements show that the neodymium ions play a network modifier role in the host glass matrix. Magnetic susceptibility data show a mictomagnetic type behaviour due to the Nd³⁺ ions present as both isolated and exchange coupled species.     

Oxidation of the intermetallics MoSi2 and TiSi2—A comparison

The oxidation behavior of two MoSi₂ variants, one Mo-rich and one Si-rich, and TiSi₂ was investigated between 1000 and 1400°C in air, oxygen and an 80/20-Ar/O₂ mixture. A protective SiO₂ scale develops on MoSi₂ in all atmospheres in the temperature range investigated. The SiO₂ modification changes around 1300°C from tridymite to cristobalite. This change in SiO₂ modification seems to cause an enhanced formation of SiO₂ and evaporation of MoO₃. The SiO₂ grows at the MoSi₂-scale interface. In air a two-layer scale grows on TiSi₂ between about 1000 and 1200°C with an inner inwards growing fine-grain mixture of SiO₂ + TiO₂ and an outer outward-growing TiO₂ partial layer. TiN formation in the transient oxidation is responsible for the formation of the inner mixed partial layer because in N -free atmospheres a scale of a SiO₂ matrix with some Ti oxide precipitates inside is formed. A one-layer scale structure similar as that in N-free atmosphere is found on TiSi₂ in air at T > 1200°C. In oxygen the TiO₂ precipitates grow as needles mostly oriented perpendicular to the surface. Due to the faster oxygen transport in TiO₂ compared with SiO₂, these TiO₂ needles act as oxygen pipes, causing an enhanced oxidation of TiSi₂ in front of these needles. The SiO₂ scale dissolves about 1–2% TiO₂. This doping causes a mixed oxygenand Si transport with the consequence that the SiO₂ scale on TiSi₂ grows partly by oxygen transport inwards and Si transport outwards. The SiO₂ modification is cristobalite over the entire temperature range investigated.     

Electrical conductivities and crystal and band-electronic structures of a new phase of BEDT—TTF—bromide salt, (BEDT—TTF)2Br(H2O)3

A new bromide salt of BEDT-TTF, (BEDT-TTF)₂Br(H₂O)₃, was obtained by an electrochemical crystallization of the tetrahydrofuran (THF) solution containing BEDT-TTF, malonic acid, and aqueous tetrabutylammonium hydroxide. Commercially available aqueous Bu₄NOH contaminates Br⁻, which is the anion source of this salt. The temperature dependence of the electrical resistance showed a complex behavior, but the resistance decrease in the low temperature range suggests a metallic ground state down to 4.2 K. Its crystal structure belongs to the δ-type, the example of which was found for δ-(BEDT-TTF)₂AuBr₂. A tight-binding band structure calculation revealed a closed Fermi surface, characteristic of a two-dimensional band structure.     

Temperature and pressure dependence of the resistivity of β-(BEDT-TTF)2X (X = I3, I2Au) and αt-(BEDT-TTF)2I3

The temperature dependence of the resistivity of the organic metals and superconductors β-(BEDT-TTF)₂I₃, β-(BEDT-TTF)₂I₂Au and α_t(BEDT-TTF)₂I₃ was measured at ambient and at several isotropic pressures (up to 2.5 kbar). By the application of a relatively low pressure, it is possible to measure the term in the resistivity that is linear in temperature. This term is masked by the larger T² term at ambient pressure. It is shown that in the temperature range below 120 K, the external modes are mainly responsible for the resistivity, while above this temperature the flipping of the CH₂ groups becomes important. The linear electron-phonon coupling corresponds to a value of λ between 1 and 1.5.     

X-ray evidence for structural changes in the organic conductors, α-(BEDT-TTF)2I3, α-(BEDT-TTF)2IBr2 and ß-(BEDT-TTF)2I3

Interrelations are investigated between the electrical and structural properties of organic conductors, BEDT-TTF (bis(ethylenedithiolo)tetrathiafulvalene) trihalides. In α-)BEDT-TTF)₂I₃ evidence is obtained by X-ray diffraction for BEDT-TTF molecular dimerization at the metal-insulator transition temperature of 135 K. Another BEDT-TTF molecular dimerization is found in α-(BEDT-TTF)₂IBr₂, which has semiconducting properties and an activation energy that increases with decreasing temperature. These dimerizations are considered to be responsible for the changes in the electrical properties. Superconducting ß-(BEDT-TTF)₂I₃ is found to have a superstructure below 175 K, above which short-range fluctuations are observed up to about 200 K.     

Phonon thermal transport properties of XB2(X = Mg and Al)compounds: considering quantum confinement and electron–phonon interaction

XB₂(X=Mg and Al) compounds have drawn great attention for their superior electronic characteristics and potential applications in semiconductors and superconductors.The study of phonon thermal transport properties of XB₂ is significant to their application and mechanism behind research.In this work,the phonon thermal transport properties of three-dimensional (3D) and two-dimensional (2D) XB₂ were studied by first-principles calculations.After considering the elec...     

Non-isothermal decomposition kinetics and lifetime of Tb2(0-MBA)6(PHEN)2

The thermal decomposition of Tb2(O-MBA)6(PHEN)2 (O-MBA: o-methylbenzoate; PHEN: 1,10-phenanthroline) and its kinetics were studied under the non-isothermal condition by thermogravimetry-derivative thermogravimetry (TG-DTG) techniques. Kinetic parameters were obtained from analysis of TG-DTG curves by the Achar method and the Madhusudanan-Krishnan-Ninan (MKN) method. The most probable mechanism function was suggested by comparing the kinetic parameters. The kinetic equation for the first stage can be expressed as dcddt = Aexp(-E/RT) 3(1 - α)2/3 The lifetime equation at mass loss of 10% was deduced as lnr= -28.7429 + 19797.795/Tby isothermal thermogravimetric analysis.     

Hydrogen defects in α-Al2O3 and water weakening of sapphire and alumina ceramics between 600 and 1000°C—I. Infrared characterization of defects

Hydrogen impurities in materials influence their properties, including flow strength. α-Al₂O₃ single crystals and polycrystalline ceramics were annealed in supercritical water between 850 and 1025°C, under pressures in the range 1500–2000 MPa. A few specimens were further subjected to plastic deformation. Hydrogen penetration was examined using infrared absorption measurements of O–H bond vibrations, which revealed two kinds of hydrogen defects. In single crystals, defects are characterized by sharp O–H absorption bands assigned to interstitial protons. Hydrogen impurities of hydrothermally annealed ceramics and of all hydrothermally deformed specimens are characterized by broad O–H bands assigned to molecular water. The grain boundaries of hydrothermally annealed ceramics are severely damaged. The kinetics of hydrogen penetration is consistent with diffusion data.     

Effect of Al content on the phase structure and the hydrogenation characteristic of La(Mg_(1-x)Al_x) alloys

1. Introduction Hydrogen-absorbing materials like sodium alanates, advanced BCC alloys, and Mg-based al- loys have been widely investigated [1]. Mg-based alloys are attractive as potential hydrogen storage materials because of their high storage capacity and low cost [2-3]. The hydrogen desorption kinetics has been improved using various methods [4-6], espe- cially alloying. It was reported that the kinetics of hydriding and dehydriding of Mg-based alloys can be improved by alloying with rar…     

The Fluidity of Al-Cu-Si Alloys—A Discussion of the Paper by Garbellini,Palacio and Biloni (1990)

Abstract

The fluidity results by Garbellini, Palacio and Biloni¹ are re-evaluated using metallurgical information from the phase fields indicated by the equilibrium phase diagram. This allows the locii of the eutectic valleys and the ternary eutectic minima to be located. These are taken to correspond to equivalent ridges and peaks on the ternary maps of the fluidity response. In this way, the data can be interpreted with greater clarity, and with greatly improved accuracy of interpolation and extrapolation. The technique is recommended for the analysis of future ternary data on fluidity and other casting parameters which may be sensitive to the mode of solidification.     

The homogeneity ranges of the delta (δ) and gamma (γ) phases of the Ni-Zn binary system grown by the reaction couple method

When investigating the diffusion layers grown by the reaction couple method at the Ni-Zn interface at 350 and 400 ‡C, the homogeneity ranges of the 5 and γ phases were found to be 87.5 ± 0.2 to 89.0 ± 0.2 at. % Zn and 73.1 ±03 to 86.2 ± 0.3 at. % Zn, respectively. Chemical compositions of the phases investigated can therefore be expressed in the simplest form as δNiZn_{7 to 8} and γNiZn_{3 to 6}.     

Study on the Inert Coordination Compound in the System of“Molybdenum(Ⅵ)—TAE—Hydroxylamine”and its Analytical Application

In the presence of ethyl alcohol or emulsifier OP,molybdenum(Ⅵ) forms 1∶1∶1'water soluble colored coordination com-pound with both of 2-(2-thiazolylazo)-5-diethylaminophenol (abbreviation TAE) and hydroxylamine.This deep bluecoordination compound is inert characteristically and remains stable in 1.7 mol/L sulfuric acid,2.4 mol/L hydrochloric or ni-tric acid.It will not be decomposed by masking agents even on boiled,while in that case,almost all the colored coordination com-pounds formed by other metal ions will be decomposed completely.This inert character of the coordination compound ofmolybdenum(Ⅵ) and its utilization in improving the analytical selectivity have been discussed.In the coexistence of various for-eign ions,especially in the presence of a great quantity of tungsten,which always interferes with the determination ofmolybdenum,the direct determination of molybdenum in the aqueous solution by applying this system has shown an acceptablesensitivity and reproducibility.From the results of determination in some synthetic and standard samples,it seems feasible to usethis system in the determination of molybdenum in nonferrous alloys.     

Mechanical properties of FeSi (ε), FeSi2 (ζα) and Mg2Si

FeSi, α-FeSi₂ (high-temperature modification) and Mg₂Si are the major phases in ferro-silicon-magnesium (FeSiMg) based foundry alloys used for the production of ductile cast iron. Small quantities of these phases were produced by induction melting for a more detailed study of the behaviour of each phase. The chemical composition of each phase was verified by electron microprobe analyses (EPMA). Investigation of the microstructure showed the existence of a small amount of second phases in the produced samples. Compression tests were performed to determine the elastic modulus of each compound. The fracture toughness of FeSi was established from three-point bending tests and was compared with values calculated from Vickers indentations. For α-FeSi₂ and Mg₂Si, the fracture toughness was estimated from hardness indentation tests. Palmqvist type cracks developed from the corners of the indentation marks in all three phases.     

The electrical conductivity and anisotropy of the molecular metal: Cs0.82[Pd(S2C2(CN)2)2]·0.5H2O

Results are presented for electrical conductivity measurements in two orthogonal directions in the molecular conductor Cs_0.82[Pd(S₂C₂(CN)₂)₂·0.5H₂O. The conduction band in this complex is believed to be via overlap of π orbitals based on the dithiolate ligands. The electrical conductivity measurements were made using the Montgomery analysis technique which compensates for the geometric shape of the crystal. Electrical conduction was found to be typically 11.0⁻¹ cm⁻¹ along the crystal (a axis) and l.0Ω⁻¹ cm"1 across the crystal (c axis). These measurements therefore give an anisotropy of around 11. The conductivity was recorded between 300 and 90 K.     

High speed temperature measurement in gear hobbing: Part I—design,concept and physical operation mode of the infrared-camera

Gear hobbing is the major technology to manufacture external gears. The motions of the tool and workpiece are dynamically linked. Therefore it is difficult to apply external measurement devices in the process. Especially the temperature, which is a vital factor to determine the load on the cutting edge, cannot be measured as easy as in other processes (for example turning). Suitable infrared-cameras are not commercially available, because these do not meet the demands for temporal and geometrical resolutions. Furthermore, commercial equipment has to be calibrated for each individual temperature (above 350 °C). This forced the Institute of Manufacturing Technology and Quality Management to develop an own measuring device. This camera is able to measure the temperature of the cutting surface within the gear hobbing process. Despite focusing the usage of the camera on hobbing in this paper, it can also be used to monitor further highly dynamical machining processes with discontinuous cutting conditions. This paper is divided into two parts. The first part describes the set-up, the concept and the physical and optical basics of the IR-camera. In the second part, the experimental realisation and the results of trials during an analogy test of the hobbing process are presented.