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 La5Cu6.33O 4S7, Cu atoms tie together the fluorite-like ∞2[La5O4S5+] and antifluorite-like ∞2[Cu6S 65-] layers of La5Cu6O 4S7. The optical band gap, Eg, of 2.0 eV was deduced from both diffuse reflectance spectra on a bulk sample of La 5Cu6O4S7 and for the (010) crystal face of a La5Cu6.33O4S7 single crystal. Transport measurements at 298 K on a bulk sample of La 5Cu6O4S7 indicated p-type metallic electrical conduction with σelectrical = 2.18 S cm -1, whereas measurements on a La5Cu6.33O 4S7 single crystal led to σelectrical = 4.5 10-3 S cm-1 along  and to semiconducting behavior. In going from La5Cu6O4S7 to La5Cu6.33O4S7, the disruption of the ∞2[Cu6S65-] layer and the decrease in the overall Cu2+ (3d9) concentration lead to a significant decrease in the electrical conductivity.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry