Search results for "Phonon"
showing 10 items of 466 documents
Coupled rotational and translational modes in the mixed molecular crystal KBr1?x (CN) x
1980
TheE g andT 2g acoustic phonon modes of the molecular crystals KBr0.96(CN)0.04 and KBr0.86(CN)0.14 have been investigated by inelastic neutron scattering at 6, 90 and 300 K. Clear resonances due to mode-mode coupling to molecular excitations were observed. In complementary ultrasonic experiments the elastic constants were found to pass through minima as a function of temperature. The results were quantitavely explained by a model which assumes simple forms of the molecular excitation spectrum. An alternative interpretation, though being only qualitative, postulates a freezing of the CN molecules into a glass-like phase.
Emission of real phonons due to electron’s self-dressing in a covalent crystal
2011
A slow monoelectronic excitation in a covalent crystal at the temperature T=0 is analyzed. The interaction with zero-point longitudinal acoustic phonons leads to the formation of a dressed electronic state at an energy level lower than that of the initial bare state. This aspect of the dressing process is described here by hypothesizing that the excess of energy is released with the emission of real phonons. Specifically, this paper considers the transition probability from the bare monoelectronic state to a dressed state of the electron accompanied by real phonons and a deformation field. The spectrum of the real phonons emitted during the electronic self-dressing is calculated by applying…
Ab initiocalculations of BaTiO3(111) surfaces
2013
The article presents the results of calculations of polar (111) surface relaxations and energetics using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. Using a hybrid B3LYP approach, the surface relaxation has been calculated for the two possible Ti and BaO3 BaTiO3 (111) surface terminations. For both Ti- and BaO3-terminated BaTiO3 (111) surfaces, the upper layer atoms relax inward. The second layer atoms, with the sole exception of Ti-terminated BaTiO3 (111) surface Ba atom, relax outward. The calculated surface relaxation energy for Ti-terminated BaTiO3 (111) surface is more than two times larger than the surface relaxation energy for BaO3-terminated BaTi…
<title>Primary radiation defect formation in silver halides</title>
1998
Under irradiation the formation of primary intrinsic defects in silver halide solid solutions AgBr1-xClx take place via strong exciton-phonon interaction. Efficiency of these defects formation depend on solid solution composition and within 0 <EQ x <EQ 0.15 dependence on temperature was observed too. Estimation shows efficiency of defects creation is approximately 0.01 for AgCl and noticeably higher for AgBr.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Electron-transfer dynamics in a donor—acceptor complex
1991
Abstract Density matrix theory is used for the study of the dissipative quantum dynamics of electron transfer in a donor—acceptor complex. The vibrational modes of the complex are divided into a single interaction coordinate coupling to the transferred electron and the remaining modes which form a dissipative environment. With increase of the coupling of the interaction coordinate to the environment and, thus, of the corresponding damping rate of the vibrational quanta, the results of the numerical calculations display a change from the coherent to the incoherent transfer regime. In contrast to the case of small values of the damping, the transfer dynamics become independent of the number o…
Vibrational Properties of InSe under Pressure: Experiment and Theory
1996
The pressure dependence of the phonon modes in the layered semiconductor γ-InSe has been investigated experimentally and theoretically for pressures up to 11 GPa. The mode Gruneisen parameters of all Raman-active zone-center phonons have been determined by Raman scattering under pressure. In addition, features corresponding to second and third-order scattering processes are apparent in the Raman spectra under resonance conditions, from which information about zone-edge modes can be obtained. For the assignment of the observed Raman features to vibrational modes we have calculated the phonon dispersion curves using a rigid-ion model including couplings to first-nearest neighbors and long-ran…
Thermal equation of state of ruthenium characterized by resistively heated diamond anvil cell
2019
AbstractThe high-pressure and high-temperature structural and chemical stability of ruthenium has been investigated via synchrotron X-ray diffraction using a resistively heated diamond anvil cell. In the present experiment, ruthenium remains stable in the hcp phase up to 150 GPa and 960 K. The thermal equation of state has been determined based upon the data collected following four different isotherms. A quasi-hydrostatic equation of state at ambient temperature has also been characterized up to 150 GPa. The measured equation of state and structural parameters have been compared to the results of ab initio simulations performed with several exchange-correlation functionals. The agreement b…
Fine tuning of thermoelectric performance in phase-separated half-Heusler compounds
2015
Two successful recipes to enhance the thermoelectric performance, namely carrier concentration optimization and reduction of thermal conductivity, have been combined and applied to the p-type (Ti/Zr/Hf)CoSb1−xSnx system. An intrinsic micrometer-scale phase separation increases the phonon scattering and reduces the lattice thermal conductivity. A substitution of 15% Sb by Sn optimizes the electronic properties. Starting from this, further improvement of the thermoelectric properties has been achieved by a fine tuning of the Ti to Hf ratio. The microstructuring of the samples was studied in detail with high-resolution synchrotron powder X-ray diffraction and element mapping electron microscop…
High-pressure structural and lattice dynamical study ofHgWO4
2010
We have synthesized monoclinic mercury tungstate $({\text{HgWO}}_{4})$ and characterized its structural and vibrational properties at room conditions. Additionally, we report the structural and lattice dynamical behavior of ${\text{HgWO}}_{4}$ under high pressure studied by means of x-ray diffraction and Raman-scattering measurements up to 16 GPa and 25 GPa, respectively. The pressure dependence of the structural parameters and Raman-active first-order phonons of monoclinic $C2/c$ ${\text{HgWO}}_{4}$ are discussed in the light of our theoretical first-principles total-energy and lattice dynamics calculations. Our measurements show that the monoclinic phase of ${\text{HgWO}}_{4}$ is stable u…
Structural and vibrational study ofZn(IO3)2combining high-pressure experiments and density-functional theory
2021
We report a characterization of the high-pressure behavior of zinc iodate, $\mathrm{Zn}{(\mathrm{I}{\mathrm{O}}_{3})}_{2}$. By the combination of x-ray diffraction, Raman spectroscopy, and first-principles calculations we have found evidence of two subtle isosymmetric structural phase transitions. We present arguments relating these transitions to a nonlinear behavior of phonons and changes induced by pressure on the coordination sphere of the iodine atoms. This fact is explained as a consequence of the formation of metavalent bonding at high pressure which is favored by the lone-electron pairs of iodine. In addition, the pressure dependence of unit-cell parameters, volume, and bond distanc…