The Superstructure of Semiconducting SmTe2-x

Abstract

SmTe1.84was synthesized and the crystal structure was studied by the single-crystal technique. The substructure was isostructural with LaTe2-x, where corrugated rock salt LaTe slabs alternate with planar tellurium square lattices. The substructure of SmTe1.84is tetragonal anti-Cu2Sb type and the superstructure is √5×√5 of the tetragonal subcell. The superstructure is tetragonal, withP42/nsymmetry,a=9.709(1) Å andc=18.007(7) Å. There are both ordered and disordered defects in the Te sheet. The superstructure obtained consists of the three possible stable solutions suggested by Lee and Foran, and all three solutions were found in a single crystal. The resistivity dependence on temperature indicates that SmTe1.84is semiconducting, which seems due to structural modulation. The structural stability of the other phases of SmTen(n=1-2) is discussed in terms of temperature and ionic radius ratio. © 1998 Academic Press.