Synthesis, Magnetic, Electrical and Mössbauer Investigations on Complex Semiconductors

Abstract

ABSTRACTThe system Ba-Fe-S contains a phase Ba1+xFe2S4 whose structure consists of infinite chains of FeS4 edge sharing tetrahedra with Fe-Fe distances of 2.7Å. The chains are 6 Å apart and Ba2+ fills the space between the chains. Each value of x designates a distinct phase and such structures have been labeled “infinitely adaptive.” The Ba1+xFe2S4 compounds are anisotropic semiconductors. The room temperature electrical conductivity for the x = 0 and x = 0.086 phases changes by nearly 6 orders of magnitude as increasing x populates the conduction band. The preparation of these materials requires very careful control of sulfur vapor pressure in closed ampules at elevated temperatures. A similar effect is observed in rare earth sulfides with the Th3P4 structure. Intrinsic La2S3 and BaLa2S4 are predicted to be high resistivity semiconductors. As the composition changes to a stoichiometry such as Ba0.8La2.2S4 the behavior becomes semi-metallic. Control of the sulfur vapor pressure will be a critical parameter for designing physical parameters into these compounds.