C-axis lattice dynamics in Bi-based cuprate superconductors

We present results of a systematic study of the c axis lattice dynamics in single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate superconductors. Our study is based on both experimental data obtained by spectral ellipsometry on single crystals and theoretical calculations. The calculations are carried out within the framework of a classical shell model, which includes long-range Coulomb interactions and short-range interactions of the Buckingham form in a system of polarizable ions. Using the same set of the shell model parameters for Bi2201, Bi2212 and Bi2223, we calculate the frequencies of the Brillouin-zone center phonon modes of A2u symmetry and suggest the phonon mode eigenvector patterns. We achieve good agreement between the calculated A2u eigenfrequencies and the experimental values of the c axis TO phonon frequencies which allows us to make a reliable phonon mode assignment for all three Bi-based cuprate superconductors. We also present the results of our shell model calculations for the Gamma-point A1g symmetry modes in Bi2201, Bi2212 and Bi2223 and suggest an assignment that is based on the published experimental Raman spectra. The superconductivity-induced phonon anomalies recently observed in the c axis infrared and resonant Raman scattering spectra in trilayer Bi2223 are consistently explained with the suggested assignment.Comment: 29 pages, 13 figure

Some reduced ternary and quaternary oxides of molybdenum containing strong metal-metal bonds. [Molybdates of ScZn, LiZn, Zn, Ba, and Na]

ScZnMo/sub 3/O/sub 8/, LiZn/sub 2/Mo/sub 3/O/sub 8/, and Zn/sub 3/Mo/sub 3/O/sub 8/ were synthesized and crystal structures were determined for the latter two. These oxides contain the same type of triangular molybdenum atom clusters found in Zn/sub 2/Mo/sub 3/O/sub 8/, but each of the trimeric clusters has available one or two additional electrons for participation in metal-metal bonding. Another new ternary oxide containing discrete metal atom clusters is Ba/sub 1/ /sub 14/Mo/sub 8/O/sub 16/. The structure of this compound consists of molybdenum-oxide cluster chains extended parallel with the c axis. The new compound NaMo/sub 4/O/sub 6/ contains infinite chains which are comprised of Mo/sub 6/O/sub 12/ clusters fused at opposite edges by removal of two edge-bridging oxygen atoms, and sharing of the metal and remaining oxygen atoms between cluster units. Another new compound, whose structure is closely related to that of NaMo/sub 4/O/sub 6/, is Ba/sub 0/ /sub 62/Mo/sub 4/O/sub 6/. This material also exhibits a sperlattice ordering of barium ions within the channels. Other compounds that have been prepared and also characterized are K/sub 2+x/Mo/sub 12/O/sub 19/, Na/sub 2+x/Mo/sub 12/O/sub 19/, and CaMo/sub 5/O/sub 8/

Structure and luminescence of some CsLnW2O8 compounds

The structure of CsLuW2O8 was determined from single-crystal X-ray diffraction data with a = 9.322(3), B = 5.132(6), C = 7.277(4) Å, and β = 95.66(4)°, in the space group P2/c. It is composed of double chains of distorted WO6 octahedra that share an edge across the chain and share opposite corners along the chain in the c direction. The tungsten-oxygen chains are interconnected via the lutetium and cesium atoms which are in eight- and twelve-coordination with oxygen. A comparison with the related structure of KYW2O8 is made. The compounds CsLnW2O8 (Ln = Y, Gd) have a similar structure. The three tungstates (Ln = Y, Gd, Lu) exhibit an intense luminescence at room temperature, whereas KYW2O8 does not luminesce at all. The luminescence of the compounds with Ln = Eu, Tb are also reported

Structure and luminescence of some CsLnW2O8 compounds

The structure of CsLuW2O8 was determined from single-crystal X-ray diffraction data with a = 9.322(3), B = 5.132(6), C = 7.277(4) Å, and β = 95.66(4)°, in the space group P2/c. It is composed of double chains of distorted WO6 octahedra that share an edge across the chain and share opposite corners along the chain in the c direction. The tungsten-oxygen chains are interconnected via the lutetium and cesium atoms which are in eight- and twelve-coordination with oxygen. A comparison with the related structure of KYW2O8 is made. The compounds CsLnW2O8 (Ln = Y, Gd) have a similar structure. The three tungstates (Ln = Y, Gd, Lu) exhibit an intense luminescence at room temperature, whereas KYW2O8 does not luminesce at all. The luminescence of the compounds with Ln = Eu, Tb are also reported

FeWO₄Cl as cathode material for lithium rechargeable battery

Lithium has been electrochemically and chemically intercalated into layered FeWP4Cl. The discharge curve between FeW04Cl and Li2FeWO4Cl is constituted by three potential plateaux and two domains where the cell voltage decreases rapidly upon the intercalation of lithium ions. A wide bi-phase domain is obtained for x in LixFeW04Cl ranging between 0.0 and 0.85. The limit of a solid solution extends in the vicinity of the LiFeWO4Cl composition. The theoretical and practical discharge capacities for Li1-xFeWO4Cl are 79.03 mAh/g and 78.45 mAh/g respectively. The structures of FeWO4Cl and LiFeWO4Cl were determined: from single crystal analysis and by Rietveld refinement of the powder X-ray diffraction pattern respectively. The modifications of the Fe-O bond lengths emphasize the iron reduction during the discharge process. Moreover, the strong change of Fe-Cl distance suggests a reversible framework modification