Lattice Vibrational Properties Research Articles

First-principles study of high-pressure phonon dispersions of wurtzite, zinc-blende, and rocksalt AlN

We present ab initio calculations of the phonon dispersions and density of states for wurtzite, zinc-blende, and rocksalt AlN under hydrostatic pressure using density functional perturbation theory. The calculations predict the full phonon dispersions throughout the Brillouin zone. Our results regarding zone-center modes for wurtzite and zinc-blende structures show generally good agreement with Raman measurements and previous theoretical data. For rocksalt structure, the present results are predictions. The different behavior of the lattice vibration properties under pressure in the three phases being studied here is discussed. The pressure coefficients and mode Grüneisen parameters are determined from the pressure dependence of vibration modes.

Molecular dynamics simulation of lattice vibration and elastic properties in nanoparticles

Elastic response and atomistic vibration of these materials are simulated by means of molecular dynamics simulation. The embedded atom method potential for copper is used to express the interaction of atoms. About 37000 atoms are contained in a simulation system. As an initial condition, atomic systems are kept in high temperature molten states (1800 K), and the systems are quenched to 0 K and relaxed to make a particle of amorphous state. The particle of crystalline state is also produced by slowly cooling the molten particles. The structure of the systems is examined through the cross sectional view and the radial distribution function. An Elastic sinusoidal displacement are applied and the vibration of atoms are monitored. Propagation of phonons thorough the nanoparticles is also simulated.

Lattice vibration and optical properties of crystalline Nd:KLu(WO 4) 2

Crystalline Nd:KLu(WO 4) 2 has been grown by the top-seeded-solution growth (TSSG) method. The polarized Raman spectrum, infrared spectrum, polarized absorption spectrum and fluorescence spectrum have been recorded at room temperature. The lattice vibration modes were calculated using space group theory and the infrared transmission spectrum was used as a supplement to the Raman spectrum to assign the modes more accurately. The Judd–Ofelt theory was used to study some important spectroscopic parameters, which were also compared with some other Nd 3+ doped double tungstates.

Band structure and lattice vibration properties of III-P ternary alloys

Electronic band structure, optical and vibrational properties of zinc-blende GaP x Sb 1− x and GaAs 1− x P x ternary alloys are obtained from pseudo-potential calculations. Comparisons are made with the available experimental values and with data obtained in previous theoretical studies. These comparisons show generally good agreement between the present results and experiment. The direct and indirect band-gap energies, the transverse effective charge, and the longitudinal and transversal optical phonon energies show a non-linear behavior with varying the composition x. The ionicity of the materials of interest is discussed in terms of the antisymmetric gap.

Lattice vibrational properties of ZnMgO grown by pulsed laser deposition

Vibrational modes were studied in n-type and p-type ZnMgO films doped with P (Mg composition of 7at.%) grown by pulsed laser deposition on sapphire. The characteristic phonon frequencies were deduced from the analysis of IR reflectance measured by Fourier-transform spectroscopy. From comparison with similarly grown ZnO (P) films, Mg incorporation reduced the frequency of TO phonons by 14.5cm−1 and introduced two Mg related modes near 530 and 969cm−1. The first is likely to belong to the local vibrational mode of substitutional Mg, and the second is tentatively attributed to strongly lattice relaxed off-center Mg atoms. In addition, it was found that Mg incorporation triggers the formation of two phonon bands with characteristic frequencies of 501 and 634cm−1 that most likely belong to lattice defects.

Elastic properties and optical phonon frequencies of zinc-blende ScxGa1−xN

Based on the empirical pseudopotential method within the virtual crystal approximation combined with the Harrison bond-orbital model, the elastic and lattice vibration properties of GaN, ScN and their hypothetical semiconducting alloys ScxGa1−xN in the zinc-blende structure have been investigated. Quantities such as elastic constants, bulk modulus, shear modulus, refractive index, dielectric constants and optical phonon frequencies were calculated as a function of the scandium molar fraction x. The agreement between the present results and the known data that are available only for GaN is generally satisfactory. Our results for ScxGa1−xN (0 < x ⩽ 1) are predictions.

Radiative Properties of the Blue BaAl2S4 : Eu2 + Phosphor

The optical properties of doped with were investigated. The synthesis was performed in evacuated and sealed quartz ampul at 1000°C during 1 h, then at 840°C during 20 h. With absorption, excitation, and emission spectra we have determined the crystal-field splitting, the redshift, the influence of the lattice vibration properties, and the thermal quenching of the luminescence. The crystal-field splitting of in was estimated on the order of 8000 to and the Huang-Rhys parameter corresponds to an intermediate electron-phonon coupling regime. The mean phonon energy for was evaluated by optical and Raman methods, and the obtained values were and 40 meV, respectively. These results confirm the very interesting properties of this blue phosphor, the most important being the very slight thermal quenching of the luminescence.

Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC)

Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC) have been presented by including the effects of free-carrier doping and three-body interactions in the rigid shell model. The short-range overlap repulsion is operative up to the second neighbour ions. An excellent agreement has been obtained between theory and experiment for their phonon dispersion curves and Debye temperature variations. It is concluded that the contributions of free-carrier doping and three-body interactions are essential for the description of the lattice dynamics of these carbides.

Electron spectroscopy of dilute nitrides

The application of electron spectroscopies in dilute nitride semiconductor research for bothchemical analysis and the determination of electronic and lattice vibrational properties isdescribed. X-ray photoelectron spectroscopy of the nitrogen bonding configurations in diluteInNxSb1−x andInNxAs1−x alloysis presented. High resolution electron-energy-loss spectroscopy (HREELS) of the plasmon excitationsin InNxSb1−x is shown to provide information on the electronic properties of the material, before andafter annealing. HREELS is also used to investigate the GaN-like phonon modes inGaNxAs1−x alloys.

Relationship between microwave and lattice vibration properties in Ba(Zn1/3Nb2/3)O3-based microwave dielectric ceramics

The dielectric properties of (1 − x)Ba(Zn1/3Nb2/3)O3–xBa (Ga1/2Ta1/2)O3 (BZN–xBGT) microwave (MW) ceramics, with x between 0 and 0.2, and those of 0.9Ba(Zn0.6Co0.4)1/3Nb2/3O3–0.1Ba(Ga0.5Ta0.5)O3 (BZCN–BGT) were studied at MW, terahertz (THz) and infrared (IR) frequencies at temperatures from 10 to 300 K. At room temperature, the temperature coefficient of resonance frequency (τf) near 3 GHz decreases from 28 ppm K−1 in undoped BZN to 2 ppm K−1 in BZN–0.2BGT and reduces to zero in BZCN–BGT. The addition of BGT to BZN depresses the dielectric Q value, but incorporation of Co improves the Q values, yielding Q ∼ 30 000 at 3 GHZ in BZCN–BGT. The relative permittivity (ε′) exhibits only limited variation with composition (ε′ values in the range 34.4–36.0). IR and THz spectra as well as the low-temperature MW dielectric measurements revealed a weak dielectric relaxation below phonon frequencies, possibly arising from charges caused by inhomogeneous distribution of the B-site ions with differing valences. The IR reflectivity spectrum of BZN–0.2BGT is significantly different (smeared) compared with other compositions, which may be caused by disorder on the B sites and by an amorphous phase at the grain boundaries.

Lattice vibration and microwave dielectric properties of (Ba1-xCax)(Mg1/3Ta2/3)O3

Lattice vibration and microwave dielectric properties of (Ba1-xCax)(Mg1/3Ta2/3)O3

Lattice dynamics of CuAu-orderedCuInSe2

The lattice vibrational properties of ${\mathrm{CuInSe}}_{2}$ with CuAu-type ordering of the cation sublattice are investigated theoretically by a first-principles calculations of the structure and the lattice dynamical characteristics including zone-center optical mode frequencies, phonon dispersion and density of states, and elastic constants. The results obtained for CuAu-ordered ${\mathrm{CuInSe}}_{2}$ are compared with related experimental data and comparative theoretical calculations for the chalcopyrite phase of the compound. A critical analysis is given of the partly contradictory experimental lattice vibration data reported for chalcopyrite ${\mathrm{CuInSe}}_{2}.$

Lattice vibrational properties of TmTe

We have investigated the lattice dynamical properties of a TmTe compound by using a breathing shell model suitable for this compound. The calculated phonon dispersion curves (PDC) reveal that this compound does not show any anomaly in their phonon properties. Our results on PDC, phonon density of states and lattice specific heat reveal that the phonon properties of this compound are like the other rare earth chalcogenides, particularly Eu-chalcogenides. We emphasize the need of measurements of the complete PDC of TmTe to support the present results on the calculated phonon properties.

Vibrational properties of Ga-stabilizedδ−Puby extended x-ray absorption fine structure

Temperature-dependent extended x-ray absorption fine structure (EXAFS) spectra were measured for a 3.3 at.% Ga stabilized Pu alloy over the range $T=20--300 \mathrm{K}.$ EXAFS data were acquired at both the Ga $K\mathrm{edge}$ and the Pu ${L}_{\mathrm{III}}$ edge. Curve fits were performed to the first shell interactions to obtain pair-distance distribution widths \ensuremath{\sigma} as a function of temperature. The temperature dependence of $\ensuremath{\sigma}(T)$ was accurately modeled using a correlated-Debye model for the lattice vibrational properties, suggesting Debye-like behavior in this material. Using this formalism, we obtain pair-specific correlated-Debye temperatures ${\ensuremath{\Theta}}_{\mathrm{cD}},$ of 110.7 $\ifmmode\pm\else\textpm\fi{}1.7 \mathrm{K}$ and $202.6\ifmmode\pm\else\textpm\fi{}3.7 \mathrm{K},$ for the Pu-Pu and Ga-Pu pairs, respectively. The result for the Pu-${\ensuremath{\Theta}}_{\mathrm{cD}}$ value compares well with previous vibrational studies on $\ensuremath{\delta}\ensuremath{-}\mathrm{Pu}.$ In addition, our results represent the first unambiguous determination of Ga-specific vibrational properties in PuGa alloys, i.e, ${\ensuremath{\Theta}}_{\mathrm{cD}}$ for the Ga-Pu pair. Because the Debye temperature can be related to a measure of the lattice stiffness, these results indicate the Ga-Pu bonds are significantly stronger than the Pu-Pu bonds. This effect has important implications for lattice stabilization mechanisms in these alloys.

Raman studies on GaAs1−xBix and InAs1−xBix

The lattice vibrational properties of new semiconductor alloys, GaAs1−xBix and InAs1−xBix, are reported. These alloys, which were grown by metalorganic vapor phase epitaxy technique, contain a small amount (1.2%–3.8%) of Bi. A detail Raman scattering study of these new alloys, which exhibit weak temperature dependence of the band gap with increasing amount of Bi, is reported here. Good crystalline quality and spatial homogeneity was confirmed using micro-Raman technique. The alloys show ternary compound behavior, confirming substitutional incorporation of Bi into the lattice site. New vibrational modes observed were assigned to GaBi-like and InBi-like modes. In addition, phonon-plasmon coupled modes and vibrational modes corresponding to Bi and As materials were also observed. Results are discussed to characterize these new alloys in detail.

Effect of pressure on the phonon properties of europium chalcogenides

Lattice vibrational properties of europium chalcogenides have been investigated at high pressure by using a simple lattice dynamical model theory viz. the three-body force rigid ion model (TRIM) which includes long range three-body interaction arising due to charge transfer effects. The dispersion curves for the four Eu-chalcogenides agree reasonably well with the available experimental data. Variation of LO, TO, LA and TA phonons with pressure have also been studied at the symmetry points of the brillouin zone (BZ) for Euchalcogenides for the first time by using a lattice dynamical model theory. We have also calculated the one phonon density of states and compared them with the first order Raman scattering results. The calculation of one phonon density of states for Eu-chalcogenides has also been extended up to the phase transition pressure. We observed a pronounced shift in phonon spectrum as pressure is increased.

Lattice Vibrational Properties of SrBi2Ta2O9

AbstractSrBi2Ta2O9 is one of the layered perovskite ferroelectrics with excellent fatigue resistance and thus has gained great interest of semiconductor industries recently in non-volatile ferroelectric random access memory (FERAM) applications. The understanding of the lattice vibrational properties of this material can provide crucial information on its structure and dielectric behavior. In this work, we carried out Raman spectroscopy study of thin film, powder and single crystal SrBi2Ta2O9. At temperatures above the Curie temperature, all 12 Raman modes expected from the tetragonal (I4/mmm) structure have been observed and assigned to the 4 A1g, 6 Eg and 2 B1g modes based the polarized Raman spectra from the single crystal samples. At lower temperature, the Raman spectra have revealed all 22 A1 modes, but only 3 out of the 20 A2 modes and 5 out of the 42 B1/B2 modes were observed in the ferroelectric phase (A21am). The soft mode was found to be of A1 symmetry and appearing only when light polarization lay in the ab-plane.

Band Gap Energies and Lattice Vibrations of the Lithium Ternary Compounds LiInSe2, LiInS2, LiGaSe2 and LiGaS2

The band gap energies EG of the lithium compounds have been measured by transmittance and reflectivity measurements as well as measurements of the diffuse reflectivity. At room temperature EG=2.83 eV (LiInSe2), EG=3.56 eV (LiInS2), EG=3.13 eV (LiGaSe2) and EG=3.62 eV (LiGaS2) have been obtained presupposing a direct interband transition. In a first attempt the birefringence of LiInS2 was studied by transmittance measurements. Using infrared and Raman spectroscopy the lattice vibrational properties have been investigated.

Lattice vibrational properties of superconducting Sr 2RuO 4

The phonon spectrum of Sr 2RuO 4 superconducting compound is calculated by using an unscreened rigid ion model for the first time. The results could not be compared with the experimental measurements as these are not available so far. The calculated values of the “neutron weighted” phonon density of states (PDOS), the partial PDOS, the mean squared vibrational amplitudes have been also presented. The results bring out the general features of the phonon spectra and also the details of the participation of different atoms in the total PDOS. We emphasise for the neutron scattering measurements on this compound.

Simulation of transformation mechanism of martensites in Ni62.5Al37.5 alloy

Thermally induced L1(0) martensitic transformation in an ordered B-2 Ni62.5Al37.5 alloy has been studied by using molecular dynamics computer simulations and embedded atom method (EAM) potential. The nucleation mechanism and growth process of martensites were investigated by analyzing the difference between the lattice vibrational properties, strain distributions in transforming and non-transforming regions. The effect of the difference between vibrational properties of Ni and Al atoms on the transformation was discussed.