title: Syntheses, crystal structures, and physical properties of La5Cu6O4S7 and La5Cu6.33O4S7.
abstract: Single crystal and bulk powder samples of the quaternary lanthanum copper oxysulfides La5Cu6.33O4S7 and La5Cu6O4S7 have been prepared by means of high-temperature sealed-tube reactions and spark plasma sintering, respectively. In the structure of La 5Cu6.33O4S7, Cu atoms tie together the fluorite-like (2)infinity[La5O4S(5+)] and antifluorite-like (2) infinity[Cu6S6(5-)] layers of La5Cu6O4S7. The optical band gap, E g, of 2.0 eV was deduced from both diffuse reflectance spectra on a bulk sample of La5Cu6O4S7 and for the (010) crystal face of a La 5Cu6.33O4S7 single crystal. Transport measurements at 298 K on a bulk sample of La 5Cu 6O 4S 7 indicated p-type metallic electrical conduction with sigma electrical =2.18 S cm(-1), whereas measurements on a La 5Cu6.33O4S7 single crystal led to sigma electrical =4.5 10(-3) S cm(-1) along [100] and to semiconducting behavior. In going from La 5Cu6O4S7 to La5Cu6.33O4S7, the disruption of the (2)infinity[Cu6S6(5-)] layer and the decrease in the overall Cu(2+)(3d(9)) concentration lead to a significant decrease in the electrical conductivity.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
authors.forename: George H
authors.initials: GH
authors.lastname: Chan
authors.forename: Ming-Ling
authors.initials: ML
authors.lastname: Liu
authors.forename: Li-Dong
authors.initials: LD
authors.lastname: Chen
authors.forename: Fu-Qiang
authors.initials: FQ
authors.lastname: Huang
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Bugaris
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Wells
authors.forename: John R
authors.initials: JR
authors.lastname: Ireland
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hersam
authors.forename: Richard P
authors.initials: RP
authors.lastname: Van Duyne
authors.forename: James A
authors.initials: JA
authors.lastname: Ibers