SYNTHESIS, CRYSTAL-STRUCTURES, AND OPTICAL-PROPERTIES OF NEW QUATERNARY METAL CHALCOGENIDES OF GROUP-5 - CS2AGVS4, K2AGVSE4, RB2AGVSE4, RB2AGNBS4, AND CS2AGNBSE4

The new quaternary compounds CsAgVS4, K2AgVSe4, Rb2AgVSe4, Rb2AgNbS4, and Cs2AgNbSe4 were prepared using the reactive flux method. In this s tructure type infinite chains of edge-sharing AgQ(4)- and M(V)Q(4)-tet rahedra are running parallel to the crystallographic a-axis. The chain s are separated by alkali cations. A linear relationship between the s ize of the alkali cation A(+) and the Q-Q interchain distances was fou nd. These compounds are isostructural with the analogous quaternary co pper chalcogenides. The optical properties were studied by collecting UV/Vis transmission and reflectance spectra which allowed to derive th e optical band gaps. The colours of the vanadium compounds range from black to dark violet with optical band gaps between 1.7 and 1.8 eV. In addition, the behaviour of the samples was studied using polarized li ght. Under these experimental conditions the niobium compound Rb2AgNbS 4 changes its colour from green to red when the direction of the polar ization plane is changed by 90 degrees.