The Phonon Densities of States of AlN and ZrN

1995 ◽  
Vol 395 ◽  
Author(s):  
C.-K. Loong
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Density Of States ◽  
Neutron Spectroscopy ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Spectra ◽  
Densities Of States ◽  
The One ◽  
Dynamics Simulations

ABSTRACTPhonons are thought to play a crucial role in the high thermal conductivity of AIN and ZrN. Using time-of-flight neutron spectroscopy, we have measured the phonon spectra of A1N and ZrN up to 300 meV (2400 cm−1). The one-phonon density of states (DOS) of AIN exhibits relatively sharp bands at about 33, 63, 83 and 91 meV. In addition, distinct multiple-phonon excitations were observed at ∼173 and 255 meV. The phonon DOS of ZrN displays similar features with the corresponding phonon energies shifted toward lower energies. The measured DOS of AIN is compared with results of molecular-dynamics simulations.

Thermal Rectification in Bi-Layered Nanofilm by Molecular Dynamics

2009 ◽  
Author(s):  
Shuai-Chuang Wang ◽  
Xin-Gang Liang
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Heat Flux ◽  
Density Of States ◽  
Atomic Mass ◽  
Interfacial Thermal Resistance ◽  
Phonon Density ◽  
Total Thickness ◽  
Phonon Density Of States ◽  
Thermal Rectification

A thermal rectifier has such nature that its thermal conductance or thermal conductivity has different values with reversed heat flux direction. This work investigates the rectification of the cross-plane thermal conductivity and interfacial thermal resistance of nanoscale bi-layered films using the nonequilibrium molecular dynamics (NEMD) method. The effects of the thickness of the single layer with the total thickness constant, the ratio of the atomic mass and temperature difference in the two ends on the thermal rectification are all considered. The results of the simulations show that the thermal conductivity and the interfacial thermal resistance are different for the heat flux with opposite directions. For the composite film with two layers of the same thicknesses, the thermal conductivity is larger when the heat flux direction is from the light layer to the heavy one. The difference becomes larger when the ratio of the atomic mass in the two layers increases. Increasing the heat flux makes the rectification of thermal conductivity larger, which means that the rectification is dependent on the temperature. For the composite film with fixed total thickness, the rectification becomes smaller when the thickness of the light layer increases. When the light layer is thick enough, the rectification is found reversed, which means that the thermal conductivity is larger with the heat flux direction from the heavy layer to the light one. The phonon density of states is also calculated to explain the phenomenon, and it is found that the overlap of the phonon density of states for the two layers is almost same even if the rectification of the thermal conductivity is reversed.

One-Phonon Spectra and Effective Phonon Density-of-States in CaGa2S4

2000 ◽  
Vol 39 (S1) ◽  
pp. 307 ◽  
Author(s):  
Nazim Mamedov ◽  
Seishi Iida ◽  
Tamao Aoki-Matsumoto ◽  
Ariyuki Kato ◽  
Makoto Yamazaki ◽  
...  
Keyword(s):  
Density Of States ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Spectra

NONLINEAR DYNAMIC EXCITATIONS AND PHONONS IN NANOSYSTEMS

1994 ◽  
Vol 08 (02) ◽  
pp. 103-111
Author(s):  
W. SCHOMMERS ◽  
H. KLANN ◽  
C. POLITIS ◽  
P. PAPANIKOLAOU ◽  
N. ATHANASIOU
Keyword(s):  
Molecular Dynamics ◽  
Density Of States ◽  
Interaction Potential ◽  
Nonlinear Dynamic ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Precise Knowledge ◽  
Cluster Properties ◽  
Dynamic Excitations ◽  
Reliable Interaction

The phonon density of states for nanoclusters has been studied theoretically using molecular dynamics; in this way, anharmonic effects could be fully considered. Comparisons are made with results obtained from bulk calculations. The cluster properties have been studied for several particle numbers and temperatures. It turned out that the properties of clusters are sensitive to small variations in the interactions between the particles. Therefore, in the calculation of cluster properties, the precise knowledge of the interaction is necessary. In our study, we have chosen krypton nanosystems because for this substance, a reliable interaction potential is available. First estimations have also been performed for metal (Al, Pb) systems.

Phonon density of states of model ferroelectrics

2010 ◽  
Vol 1262 ◽  
Author(s):  
Narayani Choudhury ◽  
Alexander I Kolesnikov ◽  
Helmut Schober ◽  
Eric J Walter ◽  
Mark Johnson ◽  
...  
Keyword(s):  
Density Of States ◽  
First Principles ◽  
Density Functional ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Cubic Phase ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Spectra ◽  
Quantum Paraelectric

AbstractFirst principles density functional calculations and inelastic neutron scattering measurements have been used to study the variations of the phonon density of states of PbTiO3 and SrTiO3 as a function of temperature. The phonon spectra of the quantum paraelectric SrTiO3 is found to be fundamentally distinct from those of ferroelectric PbTiO3 and BaTiO3. SrTiO3 has a large 70-90 meV phonon band-gap in both the low temperature antiferrodistortive tetragonal phase and in the high temperature cubic phase.Key bonding changes in these perovskites lead to spectacular differences in their observed phonon density of states.

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