ISSN:0370-1972    

DOI:10.1002/pssb.2221940234

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221940235

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractCharge transfer in GaP and InP is analysed using our precise and extensive X‐ray diffraction data. The direction and the amount of charge transfer are inferred by plotting and comparing the structure factors of the components (both observed and calculated). The charge transfer parameters thus obtained are 0.45ē from Ga to P and 0.36ē from In t

ISSN:0370-1972    

DOI:10.1002/pssb.2221940202

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractNon‐planar cracks, propagating along crystallographic directions in the cleavage fracture of brittle materials and fluctuating about a mean plane, are represented in a simple model by a distribution of sinusoidal edge dislocations in a linear elastic medium; the dislocations are perpendicular to the crack propagation direction. The opening mode I loading is assumed. It is shown that, at the front of the sinusoidal crack and out of the mean fracture plane, the stresses are bounded and the derivativeGof the energy decrease of the system with respect to crack area is zero. Only the positions of the crack front located on the mean fracture plane are associated with a nonzero value ofGalways lower than the well‐known crack opening forceG0=K 12(1−v2)/Eper unit edge length of the planar crack (K1is the stress intensity factor of mode I loading andEis Young's modulus). It is concluded that the sinusoidal crack cannot start propagating from positions on the crack front that are out of the mean fracture plane; instead, crack propagation could begin very near to the intersections of the crack front with the mean fracture plane if certain assumptions about the anisotropy of the surface energy a

ISSN:0370-1972    

DOI:10.1002/pssb.2221940203

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA new method based on Zener relaxation is elaborated for the determination of substitutional interactions in metal solid solutions. The method consists in computer simulation of temperatures of internal friction peaks taking into account the different values of effective interchange energies. Then comparison between the calculated spectra and the experimental ones is performed. It is suggested that substitutional interaction affects the atomic arrangement in creating short‐range order and shifts the energy of the substitutional atom and therefore the activation energy of internal friction. Experimental parameters of Zener relaxation are used to study the interaction energies of Cu‐Zn, AuAg, and CuAl alloys. The energies are close to those determined by diffuse scattering of X‐rays or

ISSN:0370-1972    

DOI:10.1002/pssb.2221940204

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe low‐temperature heat capacity of nonstoichiometric niobium and tantalum carbides in disordered and ordered states is measured by an adiabatic calorimetry method. It is found that in the temperature interval from 4 to 300 K the investigated ordered carbides have a higher heat capacity than the disordered carbides of the same composition. The effect of ordering on the heat capacity of nonstoichiometric carbides is interpreted in terms of the order parameter functional (OPF) method. Changes in heat capacity due to ordering in niobium and tantalum carbides are calculated. The degree of long‐range order in ordered carbides is estimated by comparing of the calculated and experimental resu

ISSN:0370-1972    

DOI:10.1002/pssb.2221940205

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe self‐consistent quasiharmonic model is used to describe the equilibrium atomic structure of a crystal and the thermodynamical properties of vacancies at high temperature. It is shown that an increase in the amplitude of the thermal atomic vibrations with temperature leads to a considerable reduction of the vacancy formation energy in the high‐temperature region, which results in the generation of a large number of defects near the melting point and, as a consequence, in the significant softening of the acoustic vibration modes of the crystal. The effective attraction between the vacancies through the phonon subsystem of the crystal is found to lead to the first‐order phase transition with a discontinuous change in the defect concentration at the transition point. The melting lines are calculated for the rare gas crystals. The effects of the solid–vapour interface on the kinetics of the solid‐liquid transition ar

ISSN:0370-1972    

DOI:10.1002/pssb.2221940206

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA theoretical study of the thermodynamic properties in the Einstein‐Debye approximation is made for solids with polyatomic basis. Analytical expressions are derived for the equation of state, isobaric specific heat (Cp), and linear thermal expansion coefficient (αP). The temperature dependences ofCpand αpare determined by four characteristic parameters of the solid: the Debye temperature θD, the Einstein temperature θE, and the Grüneisen parameters γ Gacand γ GOPassociated with the volume dependences of θDand θE, respectively. It is shown that the differenceCP−CVbetween the calculated isobaric and isochoric specific heat capacities is very small at low temperatures (T≪ θD) and increases markedly at higher temperatures. In the high‐temperature range (T≫ θE),CPis almost independent of temperature and is determined by a simple combination of the Grüneisen parameters γ Gacand γ GOP. The results obtained for αP, in the low‐ and high‐temperature limits, are in accord with those found for the asym

ISSN:0370-1972    

DOI:10.1002/pssb.2221940207

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractRaman scattering (RS) in CdAs2semiconducting crystals has been studied. The RS spectra have been recorded in the backscattering configuration with the λ = 514.5 nm line of an ion argon laser at 50 mW output level, at room temperature. The recorded RS spectra have brought some evidence of the quasi‐molecular character of the crystal lattice dynamics. The phonon modes at frequencies within the interval 180 to 270 cm−1are attributed to the arsenic atom‐chain oscillations. There is some evidence of correlation splitting to occur for these high‐frequency phonons. The modes at frequencies inferior to about 180 cm−1are attributed to the ones with important contribution of cadmium atoms and they resemble external modes in molecula

ISSN:0370-1972    

DOI:10.1002/pssb.2221940208

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe present paper reports on experimental results on polycrystalline NaNO2employing the dc resistivity, DTA, and unit cell parameters (measured by X‐ray diffractometry) in the temperature range from 298 to 480K. All the presented results confirm, in addition to the well‐known phase transitions at 436.5 and 438 K, the existence of a second‐order phase transition occurring at 448 K. We found clear evidences that the ferroelectric phase transition of NaNO2is of second order close to the first‐order one, and the rotation of the NO 2−radical mostly takes place around thec‐axis. The high‐temperature phase transformation occurring at 448 K is thought to be due to the completely disordered arrangement of the NO 2−radicals in the normal

ISSN:0370-1972    

DOI:10.1002/pssb.2221940209

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY