On a biphononic origin of the 1125 cm^(-1) absorption band in cuprous oxide

We report on the IR spectroscopic studies in both reflection (50-900 cm^{-1}) and transmission (900-3000 cm^{-1}) mode of the vibration spectrum of the cuprous oxide. A detailed analysis based on a comparison of the temperature dependences of the absorption band at 1125 cm^{-1} and of IR and Raman active fundamental vibrations results in assignment of the former to a biphonon.Comment: 5 pages, 5 figures (to appear in Phys.Lett. A

The monoclinic phase of PZT ceramics: Raman and phenomenological theory studies

This work reports on the first Raman detection of the tetragonal to monoclinic phase transition in PZT ceramics near morphotropic phase boundary at low temperatures. The transition is characterized by changes in the frequency of lattice modes with the temperature. The results presented here confirm the previous one recently reported by Noheda et al. using high-resolution synchrotron X-ray powder diffraction technique and dielectric measurements. The stability of the new phase is discussed within the framework of phenomenological Landau-Devonshire Theory.Comment: 6 pages including 4 figures, Latex, submitted to Applied Physics Letter

Quantum saturation and condensation of excitons in Cu2_2O: a theoretical study

Recent experiments on high density excitons in Cu$_2$O provide evidence for degenerate quantum statistics and Bose-Einstein condensation of this nearly ideal gas. We model the time dependence of this bosonic system including exciton decay mechanisms, energy exchange with phonons, and interconversion between ortho (triplet-state) and para (singlet-state) excitons, using parameters for the excitonic decay, the coupling to acoustic and low-lying optical phonons, Auger recombination, and ortho-para interconversion derived from experiment. The single adjustable parameter in our model is the optical-phonon cooling rate for Auger and laser-produced hot excitons. We show that the orthoexcitons move along the phase boundary without crossing it (i.e., exhibit a ``quantum saturation''), as a consequence of the balance of entropy changes due to cooling of excitons by phonons and heating by the non-radiative Auger two-exciton recombination process. The Auger annihilation rate for para-para collisions is much smaller than that for ortho-para and ortho-ortho collisions, explaining why, under the given experimental conditions, the paraexcitons condense while the orthoexcitons fail to do so.Comment: Revised to improve clarity and physical content 18 pages, revtex, figures available from G. Kavoulakis, Physics Department, University of Illinois, Urban

Contribution à l'étude de la bande fondamentale de vibration du réseau de la cuprite à 146 cm-1

A reflectance study of the fundamental absorption band due to lattice vibrations of cuprous oxide (Cu 2O) has been carried out at room temperature. The prismatic form of the samples allowed a Kramers-Kronig and a classical dispersion analysis of the reflectance of their first surface only. The optical constants, the absorption coefficient and the real and imaginary parts of the dielectric constant have been deduced. The damping constant and the oscillator strength have been determined. A brief discussion of the ionicity of Cu2O has been given by means of an effective charge calculation.Une étude par réflexion d'une des bandes fondamentales de vibration du réseau de la cuprite (Cu2O) a été entreprise à température ordinaire. La forme prismatique des échantillons a permis l'analyse Kramers-Kronig et l'analyse fondée sur la théorie de la dispersion classique du pouvoir réflecteur de la première surface seule. Les constantes optiques, le coefficient d'absorption ainsi que la partie réelle et imaginaire de la constante diélectrique ont été déduits. La constante d'amortissement et l'intensité d'oscillateur de la bande ont été déterminées. Une brève discussion de l'ionicité de Cu2O a été donnée à partir du calcul de la charge effective

Dynamique du réseau de l'argentite (Ag2O). Modèle des ions rigides avec interaction coulombienne

The rigid ion lattice dynamics of Ag2O is studied including coulomb interactions. The general force constants between first neighbors are determined on the basis of the infrared fundamental spectrum of Ag 2O. Dispersion curves are presented as well as the frequency distribution function. Optically inactiv modes and elastic constants are predicted.On étudie la dynamique du réseau de l'argentite (structure cuprite) à l'aide du modèle des ions rigides avec interaction coulombienne. Les forces générales d'interaction entre ions premiers voisins sont estimées à partir du spectre infrarouge fondamental d'Ag 2O. On calcule les courbes de dispersion des phonons ainsi que la fonction de distribution des fréquences. Les fréquences de vibration des modes inactifs et les constantes élastiques sont déterminées

LATTICE DYNAMICS OF CUPRITE (Cu2O)

The phonon dispersion curves of Cu2O have been calculated using a shell model which takes into account nearest neighbour O-Cu, Cu-Cu and O-O interactions, long range Coulomb interactions and the electronic polarizability of both the oxygen and the copper ions. The results are compared with the data obtained from ultrasound, infrared, Raman and inelastic neutron scattering measurements. The interrelations between fcc-Cu and Cu2O are pointed out and the influence of deformations of the electronic charge density on the phonon dispersion curves is discussed

Contribution à l'étude des bandes fondamentales de vibration du réseau de la cuprite (Cu2O)

A reflectance study of the fundamental absorption bands due to lattice vibrations of cuprous oxide (Cu2O) has been carried out at room temperature. The prismatic shape of the samples allowed a Kramers-Kronig and a classical dispersion analysis of the reflectance of their first surface only. The optical and dielectric constants and the absorption coefficient have been deduced. The damping constants and the oscillator strengths have been determined.Une étude par réflexion des bandes fondamentales de vibration du réseau de la cuprite (Cu2O) a été entreprise à température ordinaire. La forme prismatique des échantillons a permis l'analyse Kramers-Kronig et l'analyse fondée sur la théorie classique de la dispersion du pouvoir réflecteur de la première surface seule. Les constantes optiques et diélectriques ainsi que le coefficient d'absorption ont été déduits. Les constantes d'amortissement et les intensités d'oscillateur des bandes ont été déterminées

CRISTALLOGENESE ET ETUDE STRUCTURALE, THERMIQUE ET SPECTROSCOPIQUE DU P-NITROPHENOLATE DE SODIUM DIHYDRATE (NPNA) (NA(C 6H 4ONO 2).2H 2O ROLE DU GROUPEMENT ORGANIQUE ET DES LIAISONS HYDROGENE DANS LES PROPRIETES VIBRATIONNELLES ET D'ORDRE-DESORDRE. EVALUATION DES PROPRIETES OPTIQUES NON-LINEAIRES)

METZ-SCD (574632105) / SudocSudocFranceF