摘要:

AbstractA system of coupled anharmonic oscillators with fluctuations of the crystallographic lattice is considered. The anharmonicity is included as an effective field in the form of pseudoharmonic interactions. The description of the motion far from a Brownian particle embedded in the heat bath shows that the fluctuations lead to an explanation of the origin of stochastic forces appearing in the system and having the character of a black noise. The Brownian particle is, in general, non‐Markoffian if the fluctuations are taken into account, but it can be expressed as a sum of Markoffian processes at least. The appearance of fluctuations is related to the damping of motion in the heat bath formed by harmonic oscillator

ISSN:0370-1972    

DOI:10.1002/pssb.2221210104

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221210158

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221210159

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractThe block diagonalization of the dynamical matrix of β‐GaS is reported in the case of propagation perpendicular to the layers. A linear chain model that includes intralayer interactions between any atoms is introduced, the principal frequencies and the elastic constantsC33andC44are calculated. Within the model, the existence of real coupling parameters is discussed, that leads to an evaluation of the intralayer forces contribution to the elastic constants. The evolution of the interlayer interactions with pressure is studied, using previously published experimental results. Finally, as far as possible, the theoretical formulas are applied to the similar structures of ϵ‐GaSe and

ISSN:0370-1972    

DOI:10.1002/pssb.2221210105

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221210161

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221210162

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractThe deficiencies of the Fielek model, regarding the core‐shell interactions, the volume interactions, and the stability of the lattice, which so far have not been attended adequately, are removed. The improved version treats the lattice under zero stress within the framework of a mathematically more sound equilibrium condition which includes for the first time the van der Waals (vdW) attractive energy in the description of the total energy of the lattice. The vdW three‐body forces are employed in place of Krebs' scheme on account of its deficiency in respect of crystal equilibrium, arbitrary volume dependence of the screening parameter, and the assumption of the perfectly free electron gas. The isotropic force constant of the Fielek model coupling the cores with the d‐shells is replaced by the more realistic two‐body vdW forces. The theoretically sound model thus developed predicts the phonon spectrum in molybdenum and tungsten quite r

ISSN:0370-1972    

DOI:10.1002/pssb.2221210106

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221210163

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221210164

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractSeveral sharp absorption lines within the frequency range of the phonon gap of KI are shown to be due to the chalcogenocyanate centres. A resonance mode occuring near the low‐frequency gap boundary is also ascribed to the SeCN−centre. The experimental data are compared with a three‐dimensional model calculation for a monoatomic isotopic impurity centre and with a simple model for the centre of a linear molecular ion. A characterization of the gap and resonance modes is

ISSN:0370-1972    

DOI:10.1002/pssb.2221210107

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY