Phonons pressure

In order to study the vibrational properties of a single Au adatom on Cu faces, one adatom was placed on each face of the slab. Simulations were performed in the range of 300-1000"K to deduce the temperature dependence of the various quantities. The value of the lattice constant was adjusted, at each temperature, so as to result in zero pressure for the bulk system, while the atomic MSB s were determined on a layer by layer basis from equilibrium averages of the atomic density profiles. Furthermore, the phonon DOS of Au adatom was obtained from the Fourier transform of the velocity autocorrelation function. ... 

Hence the heat transport, in this case, depends on the dimension and shape of the liquid container. As we can see in Fig. 2.13, the thermal conductivity (and the specific heat) of liquid 4He decreases when pressure increases and scales with the tube diameter. At temperatures below 0.4 K, the data of thermal conductivity (eq. 2.7) follow the temperature dependence of the Debye specific heat. At higher temperatures, the thermal conductivity increases more steeply because of the viscous flow of the phonons and because of the contribution of the rotons. 

The Kieffer approach uses a harmonic description of the lattice dynamics in which the phonon frequencies are independent of temperature and pressure. A further improvement of the accuracy of the model is achieved by taking the effect of temperature and pressure on the vibrational frequencies explicitly into account. This gives better agreement with experimental heat capacity data that usually are collected at constant pressure [9],... 

The successful prediction of superconductivity in the high pressure Si phases added much credibility to the total energy approach generally. It can be argued that Si is the best understood superconductor since the existence of the phases, their structure and lattice parameters, electronic structure, phonon spectrum, electron-phonon couplings, and superconducting transition temperatures were all predicted from first principles with the atomic number and atomic mass as the main input parameters. 

Raman spectroscopy is very useful in identifying vibration modes (phonons) in solids. This means that structural changes induced by external factors (such as pressure, temperature, magnetic fields, etc.) can be explored by Raman spectroscopy. It is also a very useful technique in chemistry, as it can be used to identify molecules and radicals. On many occasions, the Raman spectrum can be considered to be like a fingerprint of a substance. 

According to the model, a perturbation at one site is transmitted to all the other sites, but the key point is that the propagation occurs via all the other molecules as a collective process as if all the molecules were connected by a network of springs. It can be seen that the model stresses the concept, already discussed above, that chemical processes at high pressure cannot be simply considered mono- or bimolecular processes. The response function X representing the collective excitations of molecules in the lattice may be viewed as an effective mechanical susceptibility of a reaction cavity subjected to the mechanical perturbation produced by a chemical reaction. It can be related to measurable properties such as elastic constants, phonon frequencies, and Debye-Waller factors and therefore can in principle be obtained from the knowledge of the crystal structure of the system of interest. A perturbation of chemical nature introduced at one site in the crystal (product molecules of a reactive process, ionized or excited host molecules, etc.) acts on all the surrounding molecules with a distribution of forces in the reaction cavity that can be described as a chemical pressure. 

Anastassakis and M. Cardona, Phonons, Strains, and Pressure in Semiconductors F. H. Poliak, Effects of External Uniaxial Stress on the Optical Properties of Semiconductors and Semiconductor Microstructures... 

Figure 5 shows a typical IET spectrum obtained from an undosed Al/Al-oxide/Pb junction where the oxide layer was formed by exposing the A1 base electrode to an oxygen plasma at a partial pressure of nominally 100 mTorr for approximately 1-2 min. The sample was not removed from the vacuum chamber during fabrication. No surface contamination is evident the peaks at 945, and 3620 cm-1 are due to Al—O bulk phonon modes, and the stretching of surface hydroxyls, respectively. 

Figures 5-6 show characteristic spectra at RT and the pressure dependence of the energy of the Ag-symmetry phonons for Y123 x 6.5 and x 7. The pressure dependence of the energy of the Big-like mode is almost linear for the yttrium-based compounds we have studied. As seen in Fig.6,...

The behaviour of the phonons can be related to pressure induced structural modifications. Unfortunately, for the Y123 compounds, the variation of the bond lengths as a function of pressure has been studied only for low pressures, up to 0.56 GPa [23] and there are no data available for an independent verification of the predictions of local structural modifications. The structural hydrostatic pressure measurements have found a similar pressure dependence of the a- and c-axes for the underdoped and overdoped Y123, while, for the b axis, the underdoped exhibits a larger compression ( 20%) than the overdoped sample [23], The Raman data for low pressures... 

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