Phonon density of states in γ-, β-, and α-AgCuS

The ternary superionic conductor AgCuS was studied by means of inelastic neutron scattering at temperatures of 150 to 398 K. The experimental time-of-flight spectra were recalculated into the generalized phonon density of states G(ɛ) in an incoherent approximation. It is shown that G(ɛ) of AgCuS has a nontrivial temperature dependence over the low-energy range. The relation between the temperature dependence of G(ɛ) and the existence of a low-energy mode in AgCuS is discussed. The text was submitted by the authors in English.     

Structural control of organic conductors by uniaxial strain: θ- and α-phases of BEDT-TTF compounds

The crystalline and electronic structures of the α-phase BEDT-TTF organic superconductors were controlled by the uniaxial compression along the selected crystalline axes. We found the bandwidth to be increased by the compression parallel to the a-axis while the c-axis compression reduced the bandwidth. Similar controls were possible also in the θ-phase compounds. The a-axis compression made the material metallic although the c-axis one insulating. It is possible to systematically explain these changes in electronic properties under the uniaxial compression in terms of the changes in the electronic band structure in the conducting layer.     

Investigation of constitutional and thermal defects in the ordered β-phases CoGa and NiGa alloys by Mössbauer spectroscopy

The constitutional and thermal defect formation in the Co_100-xGa_x alloys (42⩽x⩽53) and Ni_100-xGa_x alloys (47⩽x⩽52) was studied by Mössbauer spectroscopy. The formation of both constitutional and thermal defects in the CoGa alloys was observed by the appearance of resolved quadrupole split spectral components. The influence of these defects in the NiGa system was detected only by the broadening of the absorption line. The ⁵⁷Fe probe atoms were found to populate the Nisublattice in these alloys. The highest concentration of thermal defects was found in the equiatomic composition of the NiGa alloys.     

Calculation of Be in an α-α-Λ Three-Body Model Using the Faddeev Equations

 The hypernucleus Be is investigated in an α-α-Λ three-body model using the Faddeev formalism. We use an α-α interaction in which the Pauli-forbidden states are correctly taken into account and we employ some phenomenological potentials between the α and Λ particles. We obtained two bound states for and , and three resonance states of . We studied the properties of these states by calculating the components and the expectation values of the potential for each partial wave. It is found that a few channels dominate in the α (α, Λ) and states, so that the alpha-clusters or the ⁸Be core are still alive in the nucleus. In a case where the two alpha particles are fixed on an axis the contour plots of the distribution of the Λ particle are shown. With the assistance of these plots one can visually understand that some of them are shell-model-like states while others are well developed cluster-model-like states. For the structure of Be, it is concluded that the Λ particle is loosely coupled in S- and P-wave orbits about the ⁸Be(0⁺) and ⁸Be(2⁺) core states. Finally, we discuss a redundant state in the Faddeev amplitude which could arise from the treatment of symmetrization. Received June 25, 1998; revised April 13, 1999; accepted for publication December 29, 1999     

High-resolution electron microscopy and X-ray diffraction study of intergrowth structures in α- and β-type YbAlB4 single crystals

Structural features of layered boride YbAlB₄ single crystals with YCrB₄-type (α-type) and ThMoB₄-type (β-type) phases derived from a hexagonal AlB₂-type structure were investigated by electron diffraction, high-resolution electron microscopy and X-ray diffraction. X-ray diffraction experiments indicate the existence of some structural motifs. High-resolution images clearly show that the structural motifs build the intergrown lamellar structures in the matrix. The lamellar structures can be characterized by a coherent tiling of deformed Yb hexagons, which are a common structure unit in the α- and β-type structures. The characteristic intergrown nanostructure is similar to that observed in the β-type TmAlB₄ polycrystalline sample.     

Analysis of kinetics regimes in grain boundary self-diffusion†

The evolution of self-diffusion concentration depth profiles into a bulk polycrystalline material from a thin-film tracer source was studied using the lattice Monte Carlo method. The onset of the Type-B kinetics regime from the Type-A kinetics regime was investigated for a cubic grain model, which can be expected to capture the three-dimensional nature of the problem better than the usual grain boundary slab model. The solutions of Whipple–Le Claire (derived for the constant source condition), Suzuoka (derived for the instantaneous source condition), Bokstein and colleagues (derived for the constant source condition) and Levine and MacCallum (derived for the constant source condition) are tested. All these solutions describe the tail region of the profiles well for this model (provided that a simple empirical factor in the case of the first three solutions is introduced). The intermediate Type-AB kinetics regime proposed by Divinski and Larikov between the Type-A and Type-B kinetics regimes was also investigated but could not be located from analyses of best-fit exponents. Forcing the fitting nonetheless to the tail regions shows that their analysis needs some further refinement before application to this model.     

Multiple relaxation in α- and γ-loss bands of polyethylene

Dielectric and NMR behavior of linear polyethylene was observed in the α-and γ-loss bands in order to investigate the nature of the multiple loss patterns of these loss bands. The results obtained are compared with those of mechanical measurements. In the dielectric behavior of oxidized linear polyethylene, three relaxations are found in the γ-loss band, while only one relaxation is found in the α-loss band. The β-relaxation is found as a plateau region between the α-and γ-loss bands. The loss pattern of the α-loss band is different from that for the mechanical case which is composed of three relaxations. The effects of difference in morphology, addition of diluent, and heat treatment on the multiple loss patterns are examined. The results suggest that there are two noncrystalline regions in the exterior part of lamellae, including lamellar surfaces, and the two modes of molecular motion in each of these regions are responsible for each pair of relaxations; of the three relaxations found in the γ-loss band the γ₂-relaxation is related to the dielectric α-relaxation, while the γ₁-relaxation is related to the β-relaxation. The relation between the two relaxations in each pair is similar to that between the primary relaxation due to micro-Brownian motion and the local mode relaxation of amorphous polymers which are caused by the two modes of motion of the same molecules. The γ₃-relaxation seems to be caused by some different mechanism.     

Dielectric behaviour of α-cyclodextrin,heptakis (2,3,6-tri-Omethyl)-β-cyclodextrin,randomly methylated β-cyclodextrin and low frequency Raman spectra of α- and β-cyclodextrins

The frequency and temperature dependence of the real (?′) and imaginary (?″)parts of the dielectric constant of α-cyclodrextrin (form 1; α-CD. 5.9H₂O) and α-cyclodextrin (form III; α-CD.7.6H₂O) and of the corresponding dried forms (α-CD.1.1H₂O, α-CD.2.9H₂O, respectively) has been investigated over the frequency range 0–100 k Hz and temperature range 130–350 K. In addition the dielectric behaviour has been investigated of heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin (β-CD.TRIME. 0.3H₂O) and randomly methylated β-cyclodextrin (β-CD.RAME.0.8H₂O). The dielectric behaviour is described well by Debyetype relaxation (α-disperson). All α-CD systems exhibit an additional ω-dispersion at low frequencies, which is attributed to proton transport. The fact that the ?′ values of α-CD form III are larger than those of α-CD form I is attributed to the different numbers and different strengths of the intramolecular hydrogen bonds. Form III has a stable conformation which is shown by the constant values of ?′ in the temperature range 125–250 K. By contrast, in form I the ?′ values increased linearly with temperature, indicating that the system passed through succesive conformations. The temperature dependence of ?″ and phase shift ∞ in all the specimens of α-CD (forms I, III) and fully methylated β-CD do not reveal any orderdisorder transition, because the developed hydrogen bonds ae not of the flip-flop type according to their crystal structures. The partially methylated β-CD reveals the characteristics of the order-disorder transition, which was observed before in the systems dried β-CD.2H₂O and non-dried β-CD.9.8H₂O. There is a direct relation between the hydroxyl groups of β-CD and the order-disorder transition. The order-disorder transition could also be shown in dried β-CD.2.4H₂O and non-dried β-CD.9.8H₂O samples but not in dried α-CD.1.1H₂O and non-dried a-CD.5.9H₂O samples, by low frequency Raman spectroscopy (< 180 cm^?1). The step-like temperature dependence of the band at 33.7cm^?1 reveals a transition at about 223K for both β-CD samples. In the case of α-CD samples the almost linear temperature dependence of the band at 49.1 cm^?1 does not reveal any transition.     

Evidence of different β-phases in highly protonated z-cut H:LiNbO3 waveguides by raman scattering

3 waveguides is demonstrated by the Raman scattering technique. Multimode waveguides have been produced by using pyrophosphoric, benzoic, and diluted benzoic acids as a proton source. The proton-exchanged (PE) layers are subjected to annealing (APE samples) with different rates of cooling: slow (s) and quick (q). The effect of Li-H replacing is considered in the frequency range below 800 cm^-1 and about 3500 cm^-1 (OH modes). The analysis of the spectral data leads to some important conclusions about the changes in the H:LiNbO₃ lattice. We demonstrate that applying (s) ? (q) procedures on H_xLi_1-xNbO₃ waveguides with x>0.56 leads to phase transitions between different states. The high-temperature phase modifications (metastable at room temperature) are characterized by strongly broadened q-Raman bands which imply a high degree of disorder. Although the Raman measurements support the presence of different phases in H:LiNbO₃ waveguides, some conclusions, different from those reported elsewhere, have been made. Received: 16 November 1998 / Accepted: 14 December 1998 / Published online: 24 February 1999     

Ordering of hexagonal layers in phase β- and β′-Mg2Al3

Two phases, β and β′, in Mg₂Al₃ have been compared. Structural rod-like domains composed of sets of hexagonal layers have been described. The main set containing 11 layers does not change during β′–β transformation. The short sequences of layers on the β′ phase transform into clusters in the β-phase. The centres of the domains form a superstructure with a modulation vector equal to 3/22.     

Structural and Spacial Characters of Neutron Star in Relativistic σ-ω Model

The analytical and numerical solutions of structure and curvature of two kinds of static spherically symmetric neutron stars are calculated. The results show that Ricci tensor and curvature scalar cannot denote the curly character of the space directly, however, to static spherically symmetric stars, these two quantities can present the relative curly degree of the space and the matter distribution to a certain extent.     

Excimer Emission in Norepinephrine and Epinephrine Drugs with α- and β-Cyclodextrins: Spectral and Molecular Modeling Studies

The inclusion complexation behavior of norepinephrine (NORE) and epinephrine (EPIN) with native cyclodextrins (α-CD and β-CD) were investigated by UV-visible, fluorimetry, time-resolved fluorescence, SEM, TEM, FT-IR, ¹H NMR, DSC, powder XRD and PM3 methods. Single emission was observed in aqueous solution where as dual emission (excimer) noticed in the CD solutions. Both drugs form 1:1 drug-CD complexes in lower CD concentrations and 1:2 CD-drug₂ complexes in the higher CD concentrations. Time-resolved fluorescence studies indicated that both drugs showed single exponential decay in water and biexponential decay in CD. Nano-sized self-aggregated particles of drug-CD were found by TEM studies. Molecular modeling studies indicated that aliphatic chain part of the drug was entrapped in the CD cavity. Thermodynamic parameters and binding affinity of complex formation of the CD were determined according to PM3 method. The PM3 results were in good agreement with the experimental results.     

Epitaxial growth of titanium oxide thin films on c-cut and α-cut sapphire substrates

C-cut and α-cut sapphire substrates are used to grow epitaxial titanium oxide films by pulsed-laser deposition at 700 °C under a controlled oxygen pressure in the 10⁻¹-10⁻⁵ mbar range. The rutile phase is evidenced in films whatever the substrate and the oxygen pressure while the anatase phase is only observed on c-cut sapphire substrate and for oxygen pressure down to 10⁻³ mbar. No other titanium oxide phases (i.e. TiO, Ti₂O₃ or Magneli phases) are identified despite the oxygen-deficiency observed in films grown at low oxygen pressure. According to asymmetric X-ray diffraction measurements performed on films, the main axis growth and the in-plane epitaxial relationships between titanium oxide films and sapphire substrates are found to be depending on the orientation of the sapphire basal plane and on the oxygen pressure. The anatase crystallites are highly oriented with the following epitaxial relationship . The rutile phase is (2 0 0) oriented on c-cut sapphire substrate and displays two distinct in-plane relationships: . The use of α-cut sapphire substrate leads to the growth of rutile crystallites (2 0 0) or (1 0 1) oriented. In these cases, the in-plane orientations are , respectively. For the two substrates used, schematic views of atomic arrangement of the different interfaces are proposed.     

Dynamics of redox processes and electrochromism of films of zirconium (IV) phthalocyanines with out-of-plane β-dicarbonyl ligands

The electrochromic properties of the mixed-ligand zirconium phthalocyanine complex films have been investigated. Voltammetric characteristics, absorption spectra of films as a function of potential, and curves of current and absorption at the Q-band maximum in the case of their reversible oxidation in 1 N KCl against time have been measured. An analysis of the time-current dependence allowed us to find that the dynamics of the reversible oxidation of phthalocyanine complexes in such films are determined by the codiffusion in their bulk of positive and negative carriers (as Cl^? anions) with effective diffusion coefficient D_eff = ~ 10^? 13 cm²/s. The same value of D_eff has been obtained from measurements of the curve of optical density in the region of the Q-band maximum against time.     

Kinetics of diffusion-induced grain-boundary migration in dispersion-hardened Pb−Sb alloy

A complex DIGM and discontinuous phase- dissolution reaction is revealed for the first time. The volume diffusion at the front of the complex reaction and the driving force due to coherent concentration-induced stresses are studied in aPb−Sb alloy. The activation energy for the reaction is determined. Tomsk Branch of the Institute of Structural Macrokinetics and Materials Science. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 62–65, January, 2000.     

Proton spin relaxation and self-diffusion in some ‘isotropic’ nematogens

Angular distributions of reactive scattering arising from a long-lived collision complex dissociating via a transition state that approximates to a linear rotator are predicted for H atom displacement occurring over a distribution of bending angles β with respect to the rotator axis. A conical angular distribution may be generated when only a narrow range of bending angles contributes to the reactive scattering. However, the angular distribution may take on quite different character as the distribution of bending angles becomes broader. Thus, an isotropic angular distribution is generated by a bending angle distribution which follows the spherical polar weighting P(β) ∝ sin β. Forward and backward scattering is generated by bending angle distributions favouring less strongly bent displacement, while sideways scattering is generated by a bending angle distribution favouring more strongly bent displacement. The experimental angular distribution for OH + CO reactive scattering which shows mild forward and backward peaking, corresponds to a range of bending angles for H atom displacement from the H-OCO transition state which is broadened about the nominal preferred direction β = 45° but avoids strongly bent directions with β ≈ 90°.     

Electronic and crystal structure of α- and β-CeIr2Si2

We present the results of XRD, magnetization, resistivity and specific heat measurements of CeIr₂Si₂ single crystals for both, the low-temperature α-phase and the high-temperature β-phase, respectively. The α-phase adopts the tetragonal ThCr₂Si₂-type whereas the β-phase forms in the CaBe₂Ge₂-type structure. Both the phases remain paramagnetic down to low temperatures, nevertheless both, the magnetization and resistivity exhibit pronounced anisotropy in the whole temperature range of measurements (2-300 K). Results of fitting the temperature dependence of the susceptibility within the interconfiguration-fluctuation model point to the Ce valence fluctuating between 3+ and 4+. The α-phase behaves as a Fermi-liquid (FL) at low temperatures whereas the β-phase exhibits non-Fermi-liquid (NFL) features. The results are discussed in context of other similar polymorphic compounds.