Reconstruction of FCC Crystal Lattice Dynamics from Elastic Moduli

et al. 2007

Low-temperature heat capacity of cryocrystals, which contain impurity clusters has been investigated theoretically and experimentally. Such defects might essentially enrich low-frequency part of the phonon spectrum by introducing both localized and delocalized vibrations. The effect of both types of the vibrations on the temperature dependence of the heat capacity is analyzed. Heat capacity of the disordered solid solution Kr-Ar (Ar concentration is~25%) is studied as an example of the effect of the light weakly connected impurities on the low-temperature thermodynamic characteristics of the system. The mass defect of such an impurity induces «phonon pumping» from the low-frequency part of the spectrum into the high-frequency part and decreasing the low-temperature heat capacity, while the weakened interaction between the impurity and the host atoms combined with even weaker interaction between the impurities leads to the formation of the low-temperature maximum on the heat capacity temperature dependence. The analysis performed shows that at rather high Ar concentrations, the nonmonotonous temperature dependence of the relative change in the heat capacity of solid Kr Ar 1-p p solutions is determined by excitation of delocalized high-dispersion low-frequency phonons. PACS: 63.20.-e Phonons in crystal lattice; 63.20.Mt Phonon-defect interaction; 63.50.+x Vibrational states of disordered systems; 63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions.

Section: Resultsmentioning

confidence: 99%

Section: -P Pmentioning

confidence: 96%

To the theory of rare gas alloys: heat capacity

Bagatskii

et al. 2007

“…For a fcc crystal with the nearest-neighbors interaction the matrix of the operator $ L can be represented as [23] were found from the elastic constants [24] and experimental data on heat capacity. A random distribution of impurities was realized using a generator of pseudo-random numbers distributed uniformly in the interval ( ; ) 0 1 .…”

Section: Phonon Densities Of States Of Solutions Of Solidified Inert mentioning

confidence: 99%

Evolution of discrete local levels into an impurity band in solidified inert gas solution

Kosevich

et al. 2007

The density of states g( ) w of disordered solutions of solidified inert gases have been calculated using the Jacobian matrix method. The transformation of a discrete vibrational level into an impurity zone at a growing concentration of light impurity atoms has been investigated. It is shown that a 1-10% change in the impurity concentration leads to smearing the local discrete level into an impurity band. As this occurs, additional resonance levels appear which carry important information about the impurity-impurity and impurity-basic lattice force interactions in such solutions.

“…The formation of a compressed chain 0 ( ) r r < by atoms of inert gases seems quite plausible because the period of the field created by nanotubes in the grooves is smaller than the equilibrium distance for most inert gases [9]. Note that the negative parameter of the noncentral interaction is intrinsic to many solidified gases and metals [12,13].…”

Section: Introductionmentioning

confidence: 99%

Phonon spectra and vibrational heat capacity of quasi-one-dimensional structures formed by rare gas atoms on the surface of carbon nanotube bundles

Manzhelii

2019

The features of phonon spectra and their effect on the vibrational heat capacity of linear chains of inert gas atoms adsorbed onto a substrate, which is the surface of nanotubes bound to a nanobundle. The influence of the substrate results both in a shift of the lower limit of the chain spectrum from zero, and in mechanical stress in the chain (its extension or compression) also. It is shown that in the case of a compressed chain, the non-central interaction between atoms is negative (repulsive), it results in a shift of the lower boundary of the spectrum of transverse vibrations to low frequencies and to a shortening of the part of the specific heat temperature dependence in which this dependence is close to exponential. Heterogeneity of the nanobundle structure can cause a change in the distances between atoms of the chain. It is shown both and analytically and numerically, that as a result of it, discrete levels with frequencies both above and below the quasi-continuous spectrum band can appear in the phonon spectrum of the chain. The discrete levels with frequencies below the quasi-continuous spectrum band lead to a further shortening of the temperature interval at which the temperature dependence of the specific heat is close to the exponential one.