Statistical considerations on electronic behavior of the gap states in amorphous semiconductors

The equilibrium distribution functions of the gap states taking into account the effective intrasite electronic correlation energy have been employed to discuss the electronic behaviors of amorphous semiconductors, especially to interpret the temperature dependence of dc and ac conductivity and also the effect of foreign impurity atoms on the conductivity in chalcogenide glasses. The dc conductivity of thermal activation type has been explained without assuming a negligible density of states near the Fermi level, and the gradual decrease in activation energy of conductivity with increasing impurity concentration, even in melt-quenched chalcogenide glasses, has been deduced.     

New version of the gauge theory of linear defects in crystals with a polyatomic lattice

The gauge theory of dislocations and disclinations has been generalized to the case of crystals with a polyatomic lattice. An infinite anisotropic continuous medium with dislocations and disclinations is used as a real crystal model based on the gauge group SO(3N)λT(3N).     

Hidden slow time scale of correlated motions in supercooled liquids: Multi-time correlation function approach

A three-time correlation function of particle displacements is introduced and numerically calculated by performing molecular dynamics simulations of binary soft-sphere supercooled systems. It is found that the two-dimensional representations of the three-time correlation function reveal couplings of particle motions that exist over a wide range of time scales. Furthermore, it is demonstrated that the systematic change in the second time interval in the three-time correlation function enables us to analyze how the correlations in mobility decay with time. From this analysis, the characteristic time scale of dynamical heterogeneity is quantified. We find that the dynamical heterogeneity time scale becomes much slower than the α-relaxation time as the temperature decreased.     

Corrosion behavior of solid solution (Ti,Al) N as a function of Al concentration

In this work, a series of (Ti, Al) N coatings with different Al contents were deposited on 304 stainless steel substrates by Hollow Cathode Discharge (HCD) method. The coatings were grown on 304 stainless steel substrates at 400 °C. The coatings were characterized using energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), atomic force microscopy (AFM), and microhardness test. The XRD confirmed the transition from TiN phase to (Ti, Al) N phase and then to AlN phase with increasing Al concentration in the solid solution. It was found that with increasing Al concentration the hardness of the coatings initially increased up to a maximum value of about 30 GPa at around 32 at.% of Al and then the coating hardness decreased rapidly with further increase of Al content (Al > 32 at.%). The potentiodynamic polarization analysis was carried out in 3.5 wt.% NaCl solutions to study the corrosion resistance of the coatings. From the corrosion test it can be inferred that the amount of Al atoms in the coatings plays an important role for reducing the corrosion.     

Dielectric investigations of a binary system with strong correlation of the molecules

Dielectric measurements on oriented liquid crystalline substances in the frequency range from 10 Hz to 100 kHz have been carried out. The static dielectric constant parallel to the director of both single components shows a strong decrease in relation to the expected value. In the case of the swallow-tailed compound this effect can be described by assuming an equilibrium between statistically and antiparallel oriented molecules. The second component has an extremly strong tendency to be antiparallel oriented. In the mixture of both a continuous change of the correlation was observed.     

Nonlinear susceptibility measurements in a supercooled liquid close to Tg: Growth of the correlation length and possible critical behavior

The existence of a growing correlation length associated with the strong increase of relaxation times of glass-formers close to the glass transition is still a major open question in glass physics. It has been recently proposed that the ac nonlinear susceptibility of a supercooled liquid close to the glass transition temperature T_g would be a probe of dynamical correlations. As for spin glasses, where the nonlinear susceptibility diverges at the transition, this quantity is tailored to reveal the possible “hidden” critical behavior of the glass transition. We have developed a high sensitivity experimental device to measure the nonlinear dielectric susceptibility of an insulating material at finite frequency. It measures the third harmonics of the current flowing out of a capacitor with the supercooled liquid as the dielectric layer. It is based on a bridge with two capacitors, and reaches a sensitivity better than 10^− 7 (ratio of third to first harmonics). Our first results on supercooled glycerol are presented. They clearly reveal the growing of the correlations close to the glass transition.     

X-ray determination of mean square amplitudes of lattice oscillations in compounds with ZnS structure

A general method of determination of the mean square amplitudes of lattice oscillations (MSA) for crystals with sphalerite structure is described and applied to InP. The linearity of suitable functions of the measured integral BRAGG intensities of sin² θ/λ² is used for the verification of the parameters selected for the correction of extinction and DTS. In this way the accuracy of the results is increased. The MSAs of the InP-sublattices are evaluated. According to theoretical expectations the MSAs of the P-sublattice are larger because of the greater contributions of optical phonons.     

The change of the lattice constant in heteroepitaxial silver films with increase of thickness

Deposition of silver on NaCl, KCl, and LiF with 20 Å · s⁻¹ in vacuum (5 · 10⁻⁶ torr) and electronographical determination of changes of lattice constant. Precision of measurement better than ± 0.004 Å (reflections {400} and {220}). Thickness of films from 50 to 500 Å with intervals of 10 Å. The lattice parameter of films till to 115 Å in thickness did'nt differ from the parameter of bulk silver (4.086 Å). At about 175 Å the parameter reached minimum (about 4.00 Å) and took again the parameter of bulk material with the film thickness of 215 Å. With polycrystals no changes of lattice parameters occurred. – The phenomenon is connected to growth mechanism, two-dimensional and three-dimensional nucleation and to the differences in lattice parameters of substrate and deposit.     

Stearic acid polymorphs in correlation with crystallization conditions and solvents

Stearic acid has been crystallized from various organic solvents at different crystallization conditions. — The crystal structure modifications, A, B or C of the fatty acid are correlated to the solvent properties and depend on the interplay between the effect of the crystallization conditions and the solvent/solute interactions.     

Dynamic variation in the lattice parameter of a crystal under ultrasonic treatment in X-ray diffraction experiments

The X-ray diffraction in the Laue geometry is investigated in germanium and silicon single crystals upon excitation of long-wavelength ultrasonic elastic strain waves traveling along the sample surface. The X-ray diffraction beam is bounded by a slit 0.2 mm in size, which is considerably less than the wavelength of the ultrasonic wave. The use of this slit makes it possible to separate crystal regions with a nearly homogeneous strain. As a consequence, the rocking curves stroboscopically measured in a double-crystal dispersionless scheme at different instants of time almost coincide with those for a perfect crystal with a lattice parameter varying in time. The rocking curves measured in a time-integrated mode turn out to be broadened, but their integrated intensities remain unchanged. Possible applications of the developed method are discussed.     

Electron microscopic study of zinc oxide crystals microstructure crystallizing in a double hexagonal close-packed lattice

Transmission electron microscopy and electron diffraction have been used to investigate ZnO crystals microstructure and to study structural phase transformation. The results indicate that a one-to-one correspondence between lattice defects and phase transformation in ZnO crystals exist.     

Structure, characterization, and EPR of a novel Cu(II) compound with 4-aminopyrimidine. A compound with a very high lattice symmetry

The new copper(II) coordination compound [Cu(4apm)₄(CF₃SO₃)₂](H₂O)^8/3, (in which 4apm = 4-amino-pyrimidine) is studied. This compound is investigated in detail by spectroscopy, EPR, and X-ray crystal structure analysis. The compound crystallizes in the rare cubic spacegroup Im-3m with a,b, and c = 16.823(2) Å, Z = 6. The copper(II) atom has an elongated octahedral geometry, of which the basal plane is formed by four nitrogen atoms of four monodentate ligands with a Cu–N distance of 2.010(4) Å, while the apical positions are occupied by oxygen atoms of the triflate anion with a Cu–O distance of 2.606(5) Å.     

The shoulder in the second peak of the pair correlation function of superheated liquid Fe80B20 alloy

By referencing to a series of superheated liquid Fe_100 ? xB_x (x = 0 to 100) alloys, the existence of the shoulder in the second peak of the pair correlation functions of liquid Fe₈₀B₂₀ alloy is confirmed. The shoulder is caused by the unequal opportunity of connection modes rather than the occurrence of particular types of B-centered clusters. Our model predicts that vertex sharing and face sharing of the B-centered structure units are the two significant connection modes responsible for the shoulder. This picture may fill the gap in understanding the widely different shapes of the second peak in superheated liquid and amorphous Fe₈₀B₂₀ alloy.     

Chromium phase behavior in a multi-component borosilicate glass melt

This paper reports the phase behavior of a multi-component borosilicate glass melt with 0–3 mass% Cr₂O₃ at 800–1500 °C in equilibrium with air. Both upper and lower liquidus temperatures were observed. When the temperature was between the upper and lower liquidus temperatures, eskolaite (Cr₂O₃) formed in melts with >2 mass% Cr₂O₃. Below the lower liquidus temperature, a dispersed chromate phase appeared in the melt that eventually became macroscopically segregated. The chemical durability of the glasses was virtually unaffected by chromium concentration. The particular glass studied was prototypic for vitrifying high-Cr high-level radioactive wastes stored in underground tanks at the Hanford site. The results suggest a significant potential cost benefit for Hanford tank waste cleanup through increased waste solubility in glass.     

Band structure and localization of electronic states in a fivefold symmetric quasicrystal model

A fivefold symmetric quasilattice is constructed by the self-similar transformation on Gummelt two-color decagon and a single electron tight-binding model is proposed. We reduce the Hamiltonian to five identical subsets and analyze the spectral properties. By numerical calculation, three kinds of wave functions are found, which correspond to extended, localized and intermediate states, respectively.     

Kinetics of spinodal decomposition in the Ising model with dynamic lattice liquid (DLL) dynamics

The phase separation dynamics in two-dimensional binary mixtures is studied by means of a dynamic lattice liquid (DLL) model. In contrast to other methods, a simulation based on a DLL model works properly for dense systems characterized by full occupation of the lattice sites. The DLL model is a base for the first parallel algorithm which takes into account coincidences of elementary molecular movements resulting in a local cooperative structural transformation. It permits observation of a phase separation process in a system where movements of particles are highly correlated. We have investigated the influence of the proposed dynamics on a critical temperature value of T_C, the domain growth and diffusion above and below T_C.     

Crystallization behavior in a highly driven marginal glass forming alloy

Al₉₀Sm₁₀, a marginal glass former, was rapidly solidified using Cu-block single roller melt spinning at wheel speeds of 30 and 40 m/s. The product phases of rapid solidification were identified and analyzed using high energy synchrotron X-ray diffraction (HEXRD), high resolution transmission electron microscopy, and atom probe tomography. The as-quenched structure consists of a saturated amorphous phase and nanocrystalline Al with typical length scale of about 5 nm. The appearance of a pre-peak on HEXRD diffraction patterns and a low activation energy for first crystallization as determined using the Kissinger and Ozawa methods indicate some local ordering in the amorphous phase. The devitrification phase transformation path was determined using in situ high energy synchrotron radiation. Three phases, MS1, H1, and Al₄Sm, were identified during decomposition of the amorphous phase. MS1, H1 and Al₄Sm are cubic, hexagonal and orthorhombic metastable phases, respectively.     

Asymptotic behavior for linear and nonlinear elastic waves in materials with memory

In this review, we study the Cauchy problem associated to the equation of linear and nonlinear viscoelasticity with memory.Our first point is the study of dispersive properties of the solution to the linear equation of viscoelasticity with memory. The decay estimates obtained in this first part are important to treat the corresponding nonlinear Cauchy problem.The key novelty is the fact that we admit algebraic singularities and decay at infinity for the time dependent functions in the memory kernel. This fact enables one to include models different from the classical viscoelasticity problem, where this kernel is smooth and exponentially decaying in time.