Synthesis and characterization of quaternary group XIV and XV rare-earth chalcogenides

Abstract

The reactive flux method of solid-state synthesis has been used to synthesize a variety of new rare-earth chalcogenide materials. Five selenophosphate and seven thiophosphate compounds have been synthesized including K2La(P2Se6)1/2(PSe4), K3La(PSe4)2, K4La0.67(PSe4)2, K.9-xLa1+x/3(PSe4)4 (x = 0.5), KEuPSe4, KLaP2S6, K2 La(P2S6)1/2(PS4), K3La(PS4)2, K4La0.67(PS4)2, K9-xLa1+x/3(PS4)4 (x = 0.5), K4Eu(PS4)2, and KEUPS4. By controlling experimental conditions, these structures can be placed in quasi-quaternary phase diagrams, which show the reaction conditions necessary to obtain a particular chalcophosphate compound. This group XV chemistry has been extended to group XIV chemistry by the substitution of silicon, germanium, or tin in place of phosphorus. Three new crystal structures have been found; K2EuTSe5, KEuTS4 (T = Si, Ge), and Eu8Sn4Se20. Finally, we have synthesized a series of compounds to investigate how the size of alkali-metal and rare-earth metal cations affect a given structure type. K2Y(P2S6)1/2(PS4), K2Y(P2Se6)1/2(PSe4), CS2Y(P2S6)1/2(PS4), CS2Y(P2Se6)1/2(PSe4), CS2La(P2S6)1/2(PS4), and CS2La(P2Se6)1/2(PSe4) have been synthesized and are compared to K2La(P2S6)1/2(PS4) and K2La(P2Se6)1/2(PSe4). All compounds are characterized with single crystal x-ray diffraction and can be characterized further with Raman spectroscopy, UV-Vis optical band-gap analysis, and fluorescence spectroscopy.