ISSN:0370-1972    

DOI:10.1002/pssb.2221950136

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA enneagonal tiling of the plane is proposed. A self‐similar pattern is obtained by using eight basic shapes. This pattern presents rotational symmetry and no translational invarianc

ISSN:0370-1972    

DOI:10.1002/pssb.2221950102

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe structural properties of periodic and quasiperiodic W/Ti superlattices have been investigated by means of X‐ray diffraction. Intensity attenuation of even ordered peaks occurs in the spectra of W/Ti periodic superlattices with near‐equal‐layer thicknesses. This phenomenon is theoretically explained. Two series of quasiperiodic (Fibonacci) samples are prepared, one with thickness ratiodA/dB=τ, and the otherdA/dB= 1/τ. X‐ray diffraction results of these quasiperiodic superlattices are discussed and compared. The possible application of Fibonacci films as optical elements in the soft X‐ray region is discussed. Furthermore some X‐ray diffraction spectra are simulated by computer calculation in order to understand the detailed structures. The calculated results are in good agreement with

ISSN:0370-1972    

DOI:10.1002/pssb.2221950103

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractNeutron scattering double‐crystal experiments were realized using high‐frequency ultrasonic excitation in a perfect silicon single crystal. The dependence of rocking curves on the ultrasonic amplitude was measured and compared with the dynamical theory. It was found that the method of the transfer matrix is very useful for the analysis of the influence of the acoustic wave (AW) on the diffraction in very thick crystals. In particular, the pendellösung oscillations are simply and exactly removed from the whole picture of the diffraction pattern. Some exact theoretical conclusions concerning the maximum influence of ultrasound and the deformation at the peak intensity in a double‐crystal spectrometer were also re

ISSN:0370-1972    

DOI:10.1002/pssb.2221950104

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe self‐diffusion coefficients for the monovacancy mechanism, described in terms of the Arrhenius law, are calculated for Ni, Al, and the intermetallic compound Ni3Al by computer simulation techniques. Many‐body interatomic potentials, based on the embedded atom model, are used together with the static relaxation method to study the static and dynamic properties of vacancies. The defect formation and migration energies, their corresponding relaxation volumes and vibration entropies, are evaluated. Special interest is devoted to the results obtained for Ni diffusion in Ni3Al. The present calculations predict that simple vacancy‐Ni atom interchange jumps (both of ordered and disordered types) are energetically more favourable than the correlated six‐jump cycles. Even though a difference in energies of δ = 0.35 eV favours migration via ordering jumps with respect to disordering jumps, the entropy factors behave in an opposite way suggesting that both types of jumps contribute to the Ni diffusion. Only for low temperatures (T≤ 770 K) disordering jumps can be neglected. For this case, a pre‐exponential factorD0= 0.2 × m2s

ISSN:0370-1972    

DOI:10.1002/pssb.2221950105

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe diffusion coefficient of vacancies in CuAu has been measured from the shrinkage rate of voids during annealing. The observations of voids have been carried out by transmission electron microscopy under the order‐disorder transition temperature in the temperature range between 453 and 653 K. The suppression of the diffusion of vacancies emitted from voids is seen at temperatures above 493 K. The reason is discussed briefly in comparison with the results for Cu3Au in terms of the diffusivity of vacancies around the void

ISSN:0370-1972    

DOI:10.1002/pssb.2221950106

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractLarge‐scale quantum chemical simulations of the diffusion hops of empty cation and anion vacancies, as well as F+and F centers in MgO crystals have been done. The atomic configurations for 224‐site cluster and charge density distribution are analyzed for the equilibrium and saddle‐point configurations during the defect hops. The relevant activation energy for diffusion increases monotonically in the series Va→ F+→

ISSN:0370-1972    

DOI:10.1002/pssb.2221950107

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe pressure dependence of the thermal expansivity of NaCl crystal has been studied using various relations between α and the Anderson parameter δ The variation of α with pressure has been estimated and taken into account for determining the pressure dependence of α. A comparison of the results derived from various models has been presented with available experimental data. It is found that, the Anderson power law for the pressure dependence of δ is more consistent with the experimental

ISSN:0370-1972    

DOI:10.1002/pssb.2221950108

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractHighly accurate results for the mean‐square displacement (MSD) of an atom for a nearest‐neighbor Lennard‐Jones model of a f.c.c. solid are presented. These results are obtained from the Monte‐Carlo (MC) method and the Green's function method. The dependence of MSD on the sample size (N) in the MC method and similarly the dependence of MSD on the number of wave vectors used in the calculation by the Green's function method is discussed in detail. The results are presented by both methods for the infinite sample size limit as well as for the finite sizes, i.e., 32‐, 108‐, and 256‐atom sample sizes and the same number of corresponding wave vectors. It is shown that an analytical method like the Green's function method reproduces almost exactly the results of the MC method (a completely numerical procedure) for all temperatures except at the melting point (Tm). The computing time required in the former method is only a fraction of t

ISSN:0370-1972    

DOI:10.1002/pssb.2221950109

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe LO and TO phonon frequencies and dampings have been measured by near‐infrared Raman spectroscopy both in bulk GaAs and InP. The phonon damping of the LO phonon in InP is much smaller than the LO phonon damping in GaAs. The experimentally obtained temperature dependences were compared with a theory including cubic anharmonic processes and the thermal expansion of the lattice. It is shown that the phonon damping is mainly affected by decay processes into acoustic phonon

ISSN:0370-1972    

DOI:10.1002/pssb.2221950110

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY