High resolution infrared absorption spectra, crystal field, and relaxation processes in CsCdBr_3:Pr^3+

High resolution low-temperature absorption spectra of 0.2% Pr^3+ doped CsCdBr_3 were measured in the spectral region 2000--7000 cm-1. Positions and widths of the crystal field levels within the 3H5, 3H4, 3F2, and 3F3 multiplets of the Pr^3+ main center have been determined. Hyperfine structure of several spectral lines has been found. Crystal field calculations were carried out in the framework of the semiphenomenological exchange charge model (ECM). Parameters of the ECM were determined by fitting to the measured total splittings of the 3H4 and 3H6 multiplets and to the observed in this work hyperfine splittings of the crystal field levels. One- and two-phonon relaxation rates were calculated using the phonon Green's functions of the perfect (CsCdBr_3) and locally perturbed (impurity dimer centers in CsCdBr_3:Pr^3+) crystal lattice. Comparison with the measured linewidths confirmed an essential redistribution of the phonon density of states in CsCdBr_3 crystals doped with rare-earth ions.Comment: 16 pages, 5 tables, 3 figure

TRANSITION MÉTAL-NON MÉTAL DANS LES BRONZES DE VANADIUM CuxV2O5

Les bronzes de vanadium MxV2O5 sont des oxydes non stœchiométriques qui contiennent des atomes M intercalés dans le réseau de V2O5. Le métal M est ionisé et cède des électrons au réseau. Dans le cas M = Cu, il y a x électrons cédés. Les vanadiums sont également distribués sur les trois sites différents V1, V2, V3 le long de l'axe b du 'réseau monoclinique. Les électrons occupent un site seulement. Ce site est exactement saturé pour x = 2/3. Des mesures de conductivité électrique faites sur des monocristaux parallèlement à l'axe b montrent clairement que les bronzes MxV2O5 sont des conducteurs métalliques pour x > 0,55. Quand on diminue la quantité de cuivre (c'est-à-dire le nombre d'électrons par site), on observe une transition à un état non métallique. On discute les valeurs de la conductivité électrique et de l'effet Seebeck : 1) en termes de la localisation d'Anderson due au désordre entre les ions Cu+ et les lacunes, 2) en termes de polarons comme l'a proposé Mott.The vanadium bronzes MxV2O5 are non stoichiometric oxides which have intercalated M atoms in their V2O5 lattice. The metal M is ionized and gives its electrons to the lattice. For M = Cu, there are x donated electrons. The vanadiums are equally distributed in three different sites, V1, V2 and V3 oriented along the b axis of the monoclinic lattice. The electrons occupy only one site. For x = 2/3 this site is exactly saturated. Electrical conductivity measurements made on single crystals along the b axis show clearly that the MxV2O5 bronzes are metallic conductors for x > 0.55. When the amount of copper (i. e. the number of electrons per site) becomes smaller, the authors observe a transition to a non metal. The results of the electrical conductivity and Seebeck measurements are discussed : (i) in terms of an Anderson localization due to a disorder between the Cu+ ions and the vacancies and (ii) in terms of polarons as proposed by Mott

Élaboration et caractérisation de cristaux dérivés de K3_{3}Li2_{2}Nb5_{5}O15_{15}

Good quality crystals of K$_{3}$Li$_{2}$Nb$_{5}$O$_{15}$ type were grown from the melt followed by method slow cooling using a pseudo-flux method (an excess of K$_{2}$CO$_{3}$ and Nb$_{2}$O$_{5}$ is present). The crystals were identified by X-ray diffraction, they crystallized with the tungsten bronze-type structure in the tetragonal system at room temperature. The space group is P4bm. Their composition (K$_{2.82}$(Nb–O)$_{0.08}$Li$_{1.54}$Nb$_{5}$O$_{15}$) was determined by chemical analysis. Dielectric measurements were realized along the [001] and [100] directions in the frequency range from 10$^{3}$ to $3 \times 10^{5}$ Hz. The temperature dependences of dielectric constants $\varepsilon^{\prime}_{\rm r33}$ and $\varepsilon^{\prime}_{\rm r11}$ and of birefringence $\Delta n$ show two maximums at $T_{1}\cong 100$ K and $T_{\rm C}\cong 680$ K, the latter being the ferroelectric Curie temperature.Des cristaux de bonne qualité de type K$_{3}$Li$_{2}$Nb$_{5}$O$_{15}$ et de structure “bronze” ont été élaborés par fusion et refroidissement lent en présence d'un pseudo-flux (K$_{2}$CO$_{3}$ et Nb$_{2}$O$_{5}$ en excès). L'analyse chimique montre que leur composition correspond à la formulation K$_{2,82}$(Nb–O)$_{0,08}$Li$_{1,54}$Nb$_{5}$O$_{15}$. Ces matériaux cristallisent dans le système quadratique à 295 K avec le groupe spatial P4bm. Les mesures diélectriques ont été effectuées selon deux directions [001] et [100], perpendiculaires aux grandes faces des cristaux élaborés. Les variations thermiques de la permittivité et de la biréfringence ont permis de mettre en évidence deux maxima l'un à $T_{1}\cong 100$ K selon [100], l'autre à $T_{\rm C}\cong 680$ K selon [001] ; ce dernier correspond à al température de Curie ferroélectrique

Passivation of YBa2Cu3O7 − δ single crystals by fluorination treatments

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Heavy Ions Irradiation Effects On Magnetization Of Tl2ba2cacu2o8 And Tlba2cacu2o7 Single Crystals

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Magnetization measurements were performed as a function of magnetic field and time in Tl2Ba2CaCu2O8 and TlBa2CaCu2O7 single crystals to study the effects of high energy Xe ion irradiation. The effective pinning energies at 6 K and 40 K have been evaluated from magnetic relaxation measurements. The activation energies are hardly changed after irradiation. The study of magnetization hysteresis shows that an irradiation fluence of 2 × 1011 ions cm-2 enhanced hysteresis at 6 K in both crystals. But a fluence of 1012 ions cm-2 was detrimental for the 2212 sample which is the most sensitive to heavy ion irradiation damage in the Tl-cuprate family. The magnetic hysteresis at 70 K after irradiation is more drastically increased than at 6 K. This spectacular modification is interpreted by a recovery of the 3D character of the flux line lattice. © 1992.13427928507/57630-5; FAPESP; Simons Foundation; 2013/09850-7; FAPESP; Simons Foundation; DMR-1005751; NSF; Simons Foundation; PHYS-1066293; NSF; Simons Foundation; SF; Simons FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Umezawa, Crabtree, Liu, Weber, Kwok, Nunez, Moran, Claus, (1987) Phys. Rev. B, 36, p. 7151van Dover, Gyorgy, White, Schneemeyer, Felder, Wasczak, (1990) Appl. Phys. Lett., 56, p. 2681Civale, Warwick, McElfresh, Worthington, Malozemoff, Holzberg, Thompson, Kirk, (1990) Phys. Rev. Lett., 65, p. 1164Kritscha, Sauerzopf, Weber, Crabtree, Chang, Jiang, Flux Pinning Enhancement and Shift of the Irreversibility Line by Fast Neutron Irradiation of Single Crystal Bi2Sr2CaCu2O8 (1990) Europhysics Letters (EPL), 12, p. 179Vichery, Rullier-Albenque, Pascard, Konczylowski, Kormann, Favrot, Collin, (1989) Physica C, 159, p. 697Bourgault, Bouffard, Toulemonde, Groult, Provost, Studer, Nguyen, Raveau, (1989) Phys. Rev. B, 39, p. 6549Bourgault, Hervieu, Bouffard, Groult, Raveau, (1989) Nucl. Instrum. Methods B, 42, p. 61Hardy, Groult, Hervieu, Provost, Raveau, Bouffard, (1991) Nucl. Instrum. Methods B, 54, p. 472Venturini, Barbour, Ginley, Baughman, Morosin, (1990) Appl. Phys. Lett., 56, p. 2456Osborn, (1945) Phys. Rev., 67, p. 351Yeshurun, Malozemoff, Holtzberg, Dinger, (1988) Phys. Rev. B, 38, p. 11828Campbell, Fruchter, Cabanel, (1990) Phys. Rev. Lett., 64, p. 1561Xu, Suenaga, Moodenbaugh, Welch, (1989) Phys. Rev. B, 40, p. 10882Stollman, Dam, Emmen, Pankert, (1989) Physica C, 161, p. 444Beasley, Labush, Welb, (1969) Phys. Rev., 181, p. 682Martin, Maignan, Provost, Michel, Hervieu, Tournier, Raveau, (1990) Physica C, 168, p. 8Hardy, Groult, Provost, Hervieu, Raveau, Bouffard, (1991) Physica C, 178, p. 255Raveau, Hervieu, Michel, Provost, (1989) Mater. Sci. Eng., 109 A, p. 281Hardy, Hervieu, Groult, Provost, (1991) Radiation Effects and Defects in Solids, , in the pressKopylev, Schegolev, Togonidze, Magnetization curves and low critical fields of Tl2Ba2CaCu2Ox single crystals (1989) Physica C: Superconductivity, 162-164, p. 1143Kopylev, Koshelev, Schegolev, Togonidze, The role of surface effects in magnetization of high-Tc superconductors (1990) Physica C: Superconductivity, 170, p. 291Kes, Aarts, van den Berg, van der Beek, Mydoch, (1989) Supercond. Sci. Technol., 1, p. 242Palstra, Batlogg, Scheemeyer, Wasczak, (1991) Phys. Rev. B, 43, p. 3756de Rango, Giordanengo, Tournier, Sulpice, Chaussy, Deutscher, Genicon, Raveau, The « irreversibility line » of Bi2-xPbxSr2Ca2Cu3O10 : a possible breakdown of an intrinsic proximity effect (1989) Journal de Physique, 50, p. 2857Raveau, Michel, Provost, Hervieu, The nature and the role of rock salt-type layers in superconductive layered copper oxides (1990) Solid State Ionics, 40-41, p. 785. , 1st ednV.Z. Kresin, S.A. Wolf and G. Deutscher, PreprintV. Hardy, J. Provost, D. Groult, M. Hervieu, B. Raveau, S. Durcok, E. Pollert, J.-C. Frison, J.-P. Chaminade and M. Pouchard, Physica C, accepted for publicationKonczykowski, Rullier-Albenque, Yacoby, Shaulov, Yeshurun, Lejay, (1991) Phys. Rev. B, 44, p. 7167Civale, Marwick, Worthington, Kirk, Thompson, Krusin-Elbaum, Sun, Holtzberg, (1991) Phys. Rev. Lett., 67, p. 64

The “irreversibility line” of a Tl2Ba2CaCu2O8 single crystal: Evidence for a phase transition

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