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.

Generalized phonon density of states of La2−xSrxCuO4 cuprate superconductor

2019 ◽  
Vol 33 (28) ◽  
pp. 1950328
Author(s):  
Anushri Gupta ◽  
Sanjeev K. Verma ◽  
Anita Kumari ◽  
B. D. Indu
Keyword(s):  
Density Of States ◽  
Phonon Spectrum ◽  
Quantum Dynamics ◽  
Cuprate Superconductors ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Layered Superconductor ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
The Impact

Many body quantum dynamics of phonons is steadily developed by considering the various effects of anharmonicities, defects (consider as doping or impurity concentration) and electron–phonon interactions in model Hamiltonian (instead of BCS Hamiltonian) for a high-temperature superconductor (HTS). This enables to obtain the expressions for the renormalized phonon spectrum, the renormalized phonon density of states (RPDOS). The RPDOS can be resolved into diagonal and nondiagonal parts where the nondiagonal component is found highly impurity-dependent. Considering the suitable Born–Mayer–Huggins (BMH) interaction potential, the renormalized phonon spectrum, RPDOS and generalized phonon density of states (GPDOS) of the La[Formula: see text]Sr[Formula: see text]CuO4 layered superconductor have been numerically analyzed and it was found that these quantities depend on doping concentration, anharmonicities, and temperature. The results are compared with the inelastic neutron scattering experimental data of GPDOS for La[Formula: see text]Sr[Formula: see text]CuO4 and are found in good agreement. The ratio of deviation in GPDOS to GPDOS at critical temperature ([Formula: see text] K) shows the implicit difference at [Formula: see text]. The impact of defects, anharmonicities, and electron–phonon interactions in the cuprate superconductors virtually modify the scenario of GPDOS and affirm a large number of exotic peaks in the spectrum.

PHONON DENSITY OF STATES IN THE SUPERCONDUCTING Y-Ba-Cu-O SYSTEM

1989 ◽  
Vol 03 (01) ◽  
pp. 55-59
Author(s):  
J.H. RUAN ◽  
A.S. YU ◽  
J. QIN ◽  
C. GOU ◽  
T.H. YANG ◽  
...  
Keyword(s):  
Energy Spectrum ◽  
Neutron Scattering ◽  
Density Of States ◽  
Inelastic Neutron Scattering ◽  
Meissner Effect ◽  
Inelastic Neutron ◽  
Scattering Method ◽  
Phonon Density ◽  
Large Decrease ◽  
Phonon Density Of States

The generalized phonon density of states for the high-T c superconductor YBa 2 Cu 3 O 7.1 with high Meissner effect (50%) and for its retreated sample with low Meissner effect (15%) at T=300 K and T=86 K respectively was measured by using inelastic neutron scattering method. The density of states of the superconductor YBa 2 Cu 3 O 7.1 at temperatures of both 300 K and 86 K shows a similar energy spectrum below 95 meV. However, above this energy there are evident softening of modes at 86 K. In addition, a large decrease of 92 meV peak in the density of states for a sample with lower Meissner effect was observed, this effect is supposed to be a result of an increase of vacancies on O 4 site.

Phonon density of states of tetracyanoethylene from coherent inelastic neutron scattering at Dhruva reactor

Pramana ◽  
1989 ◽  
Vol 33 (5) ◽  
pp. 595-602 ◽  
Author(s):  
S L Chaplot ◽  
R Mukhopadhyay ◽  
P R Vijayaraghavan ◽  
A S Deshpande ◽  
K R Rao
Keyword(s):  
Neutron Scattering ◽  
Density Of States ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Phonon Density ◽  
Phonon Density Of States

scholarly journals Phonon density of states for α-plutonium from density-functional theory

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Per Söderlind ◽  
Lin H. Yang
Keyword(s):  
Density Functional Theory ◽  
Specific Heat ◽  
Density Of States ◽  
Density Functional ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Monoclinic Crystal ◽  
Functional Theory ◽  
Phonon Spectra ◽  
Good Agreement

AbstractThe ground-state α phase of plutonium has an extraordinary 16-atom per cell, monoclinic crystal structure defined by 20 parameters, including the cell dimensions, not dictated by the symmetry. The electronic, magnetic, and elastic properties of this complicated material have been predicted in the past but here we compute its phonon spectra. Employing a density-functional-theory (DFT) model, that is fully relativistic and accounts for orbital–orbital coupling (orbital polarization, OP), we determine the phonon density of states of α-plutonium and find good agreement with inelastic x-ray scattering. The calculated specific heat also compares very favorably with experiment. An analysis of the partial atom-projected phonon spectra suggests that atom type 8, that is located in a more open space of the structure, dominates the intensity at very high phonon frequencies. This feature of the model is essential for a good agreement with the experimental spectra. The satisfactory comparison between theory and experiment for the phonons and specific heat suggests that the DFT (+OP) approach is appropriate and accurate for α-plutonium.

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