Lattice dynamics and debye temperature of AlCu,AlSi and AlGe alloy systems

The lattice dynamics and specific heat at constant volume for AlCu alloy system is studied using our previous treatment based on the microscopic electronic theory. Considering the volume and electron density effect on the dynamical matrix of the pure constituent, we obtain the band and local mode frequencies at the temperature-dependent specific heat in the Al_1−x Cu_x solid solution. Then, using the data about the mean elastic wave and the specific heat extrapolated to the absolute zero temperature, the Debye temperature is presented for the Al_1−xCu_x, Al_1−xSi_x and Al_1−xGe_x alloy systems. The Debye temperature decreases as a function of the Cu atomic fraction x for Al_1−xCu_x alloy, and remarkably for Al_1−xSi_x and Al_1−xGe_x solid solutions.     

The development of stress during NaKion exchange of polycrystalline β, β″-Al2O3 and its influence on the ion-exchange process

Na⁺K⁺ ion-echange at 810°C and 1200°C between high density β, β″-Al₂O₃ multiphase specimens and KClNaCl melts has been investigated. It was found that the equilibrium conditions are affected significantly by the developed stresses. Microstresses are caused by the thermal expansion anisotropy of both phases and by the difference of alkali ion diffusion rates in the two phases. Macrostresses are introduced by compositional differences between the surface and interior of the specimens. The critical condition for the appearance of microfractures has been estimated using a simplified model. Based on the determination of the distribution gradient of the two kinds of ions, the residual macrostresses have also been calculated. Analysis of these two kinds of stress suggests failure of the material when conditions are such that they act concurrently.     

Zero resistance above 90K in superconducting oxides ErBaCuO and YbBaCuO

Superconductivity transition has been observed by electrical resistance and a.c. magnetic susceptibility measurements in ErBaCuO and YbBaCuO systems. The highest T_c(ϱ=0) is 90.3K for ErBaCuO and 91K for YbBaCuO.     

Thermodynamics and phase diagrams of MoPdRu and related systems

During the irradiation of nuclear fuels up to 10% of the original fissile material (uranium and plutonium) is converted into a wide range of fission products. One particular group of fission-product elements, the transition metals Mo, Tc, Ru, Rh and Pd, are not oxidised at the quite low oxygen potentials existing in the fuels, and are precipitated in the fuel in the form of metallic inclusions. The thermodynamic properties and phase diagram of these alloys are of importance, since the precise composition of these alloys, as a function of radial position can provide important information concerning operating conditions inside a fuel pin. For this reason a thorough reassessment of these systems is under way. This paper reports values of the excess-Gibbs energies of mixing in the MoPd, PdRu and MoRu binary systems, and in the MoPdRu ternary. Calculated sections of the MoPdRu system at selected temperatures are presented.     

Surface morphology of MgO (100) crystals implanted with MeV Al+ and Al2+ ions

MgO (100) single crystals are implanted with 1.50-MeV Al⁺ and 3.00-MeV Al₂ ⁺ ions at a fluence of 1×10¹⁵ Al  atoms  cm^-2 under high-vacuum conditions. The surface morphology of the substrate is measured in air using atomic force microscopy and X-ray reflectometry followed by computer-simulated spectrum analysis. The ion-irradiated areas are found to protrude to different heights on the nanometre scale. Small height differences are observed in the areas irradiated by Al⁺ and Al₂ ⁺ ions of comparable energy, dose rate and total fluence. The results indicate that protrusions are most likely caused by implantation-induced point defects (vacancies) generated in the crystal during implantation. Other possibilities for the cause of protrusions are discussed. Thermal treatment stimulates a partial recovery of the implantation damage and alters the topography of MgO surfaces. Received: 22 May 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

The influence of morphology on grain-boundary and twin-boundary bainite growth kinetics at the bay in Fe–C–Mo

The growth kinetics morphology and crystallography of grain-boundary bainite (GBB) and twin-boundary bainite (TBB) formed in Fe–0.24?wt%?C–4?wt%?Mo were reassessed. Optical microscopy and transmission electron microscopy observations of these coalesced allotriomorphic slabs showed that the bainite–austenite growth fronts were rough, even spiky in place, characteristic of Widmanstätten growth. Furthermore, a significant substructure of regions having different ferrite orientations (subunits) was revealed, the GBB subunit arrangement was quite complex, suggestive of competitive growth between subunit, whereas TBB had a simpler subunit arrangement that yielded less subunit competition. These crystallographic and interfacial structure effects are instrumental for explaining the more rapid thickening of GBB relative to TBB. The differing subunit arrangements in GBB versus TBB originate in the differing ferrite–austenite orientation relationships established during nucleation at austenite grain boundaries versus twin boundaries. The complexities inherent in a multicrystalline allotriomorphic slab migrating with a rough growth front prevents direct interpretation of thickening kinetics data in terms of a fundamental growth process.     

Conductivity properties of proton transfer and influence of temperature on it in hydrogen-bonded systems

We study and calculate the mobility and conductivity of proton transfer and influence of temperature on it by pang's dynamic model in hydrogen bonded systems, which coincide with experiments. We further study the mechanism of magnetization of ciguid water in the basis of this model.     

X-ray photoemission studies of PtSn and PtPb bimetallic systems

The Pt(5d) and Pt(4f) in PtSn and PtPb composites produced by sequential vapor deposition have been examined by X-ray photoelectron spectroscopy. At low concentrations of Pt, the Pt(5d) becomes a single, narrow resonance at about 4 eV below the Fermi level. Its density of states at the Fermi level is small. This leads to a large suppression of the Pt(4f) lineshape asymmetry. As the Pt concentration increases, d-d interactions split the Pt(5d) resonance and increase the 5d density of states at the Fermi level by pushing one of the split resonances to the Fermi level. Consequently, the Pt(4f) lineshape asymmetry increases. The evolution of the Pt(4f) and Pt(5d) in PtSn and PtPb are very similar but different from that of small Pt particles supported on carbon. The close similarity of the electronic properties of Pt in PtSn and PtPb suggests that the poisoning of Pt by Pb is not entirely due to electronic effects although there are indications of stronger interaction between Pt and Pb than between Pt and Sn atoms. The strong surface enrichment of Pb on PtPb points to the importance of the physical blockage of Pt atoms by surface Pb in determining the poisoning effect of Pb.     

The influence of K4Fe（CN）6 on the photosensitivity of cubic AgCl microcrystal

The influence of K4Fe(CN)6 at various doping concentrations on the photosensitivity of cubic AgC1 microcrysgals has been investigated by using the microwave absorption and phase-sensitive measurement technique. The time behaviour of free photoelectrons in AgCl microcrystals is analysed by using computer simulation as a function of three parameters of shallow electron trap (SET) including doping concentration, trap depth and capture cross-section (CCS).It is found that the three parameters of SET play different roles on the free photoelectron decay time (FDT). After considering the threshold effects of the three parameters and their collective effects, the trap depth value, the CCS value,and the optimal doping concentration of the SET introduced by the dopant K4Fe(CN)6 in cubic AgCl microcrystals can also be determined, and the best photosensitivity of cubic AgCl can be obtained.     

Electron diffraction and electron microscopic study of BaYCuO superconducting materials

Electron microscopy and electron diffraction have been applied to show that the orthorhombic phase in the compound Ba₂YCu₃O_7−δ is responsible for the high superconducting transition temperature. A positive correlation is found between the volume fration of the orthorhombic phase and the superconducting transition temperature. By means of an “in-situ” heating experiment it is found that the orthorhombic phase is formed on cooling from a high temperature tetragonal phase with disordered vacancies. It is suggested that the low temperature tetragonal phase that occurs in the same specimens as the orthorhombic phase also contains an ordered arrangement of vacancies different from that present in the orthorhombic phase. The order-disorder transition associated with the structural vacancies is shown to be reversible, provided there has been no oxygen loss.     

Enhanced electrical transport in LiBrLiI mixed crystals and LiBrAl2O3 composites

LiBrLiI mixed crystals and LiBrAl₂O₃ composites have been studied by means of complex impedance analysis an conductivity, X-ray diffraction, DTA and SEM techniques. The substitution of wrong size I⁻ ions in LiBr increases the conductivity and decreases the migration energy of Li-ion vacancies. These results are consistent with those of the KBr-KI system and earlier predictions. LiBrAl₂O₃ composites exhibit a sharp increase in the conductivity. The highest conductivity obtained was ≈10⁻³ Ω⁻¹ cm⁻¹ at 302°C for LiBr + 10 m/o Al₂O₃.     

On the homogeneity range of β″-alumina in the Na2OMgOAl2O3 system

The Al₂O₃ rich region of the Na₂O:MgOAl₂O₃ system has been investigated by means of X-ray phase analytical methods. The main features of the isothermal sections at 1870 K and 1950 K have been determined. The two sections exhibit the same phase equilibria except in the Na₂Al₂O₄-β″ region where a liquids phase appears at 1950 K. The magnesium stabilized β″-alumina phase with the nominal formula Na_1xxAl₁₁−xO₁₇ exhibits an extended homogeneity range with the magnesium content ranging over x=0.59-0.72. The homogeneity ranges are accompanied by variations in the unit cell dimentions. The composition of β″-alumina appears to correspond to a far lower relative sodium cntent than that indicated by the ideal formula at large magnesium + aluminium contents.     

Superconductivity of LaMCuO system (MBa,Sr and Ca

Superconductivity of the compounds of LaMCuO system with K₂NiF₄ type structure has been studied. For the sintered compounds with MBa, Sr and Ca, the highest onset transition temperatures, T_ci, estimated from resistivity measurement are about 36.9K, 43.0K and 23.5K, respectively and the highest temperatures where the resistivity vanishes, T_cf, are about 27.8K, 34.0K and 15.5K, respectively. Almost complete Meissner effect has been confirmed by low frequency ac susceptibility measurement. Crystals of the compounds with MBa and Sr have been prepared. As the result of the preliminary experiment for a crystal with Ba, it is found that T_cf of the crystal is higher than any one of the sintered specimens with MBa, while the T_ci of the crystal is nearly the same as the highest one of the sintered specimens.     

Relativistic configuration interaction calculations on Kα X-ray satellites of magnesium ions

In this work, the multi-configuration Dirac-Fock (MCDF) and relativistic configuration interaction (RCI) methods have been used to calculate the transition wavelengths, electric dipole transition probabilities, line strengths and absorption oscillator strengths for the Kα X-ray from Mg III to Mg XI. We also take the contributions from the Breit interaction, finite nuclear mass corrections and quantum electrodynamics corrections to the initial and final levels, into account. The present values for Mg X and Mg XI were in good agreement with the previous experimental and theoretical results. The new data in this work provide reference values for the level lifetimes, charge state distributions, and average charge of magnesium plasmas.     

Systematic multi-configuration Dirac-Fock calculations of the Kα and Kβ X-ray spectra of silicon ions

The transition energies, absorption oscillator strengths, line strengths and transition probabilities between computed levels are reported for the He-like to Ne-like Silicon ion sequences. Wavefunctions were determined relativistic configuration interaction (RCI) and multi-configuration Dirac-Fock (MCDF) technique included the Breit interaction, quantum electrodynamic (QED) corrections and nuclear mass corrections. The calculated values are in good agreement with the available experimental data and the recent theoretical values obtained from other methods. These data provide reference values for the level lifetimes, charge state distributions, and average charge of silicon plasmas.     

Relaxation phenomena in Cr3+ doped Al2O3−Fe 2 57 O3 systems

Mössbauer absorption spectra have been measured for Cr³⁺ doped Al₂O₃?Fe ₂ ⁵⁷ O₃ systems for different values of the Cr³⁺ concentration at room temperature. The cross relaxation between Fe³⁺ and Cr³⁺ ions, which destroys the paramagnetic hyperfine structure of Fe⁵⁷ observed in undoped Al₂O₃?Fe ₂ ⁵⁷ O₃, is thoroughly studied. The experimental results suggest a new kind of cross-relaxation process involving three spins, i.e. two Fe³⁺.ions and one Cr³⁺. The process, though it is a higher-order one, is highly effective because it is energy-conserving.