Synthesis, crystal structure, electronic structure and electrical conductivity of La3GeSb0.31Se7 and La3SnFe0.61Se7

The selenides La3EM1-xSe7 (La6E2M2-xSe14) adopt the Ce6Al3.33S14 structure type. La3GeSb0.31Se7 and La3SnFe0.61Se7 crystallize in the non-centrosymmetric space group P6(3) with La replacing Ce in the 6c site, E = Ge or Sn replacing Al in the 2b site and M = Fe or Sb replacing the other, deficient Al site (2a). The structure contains La atoms in square antiprisms of Se atoms, isolated distorted [ESe4] tetrahedra, and face sharing distorted [MSe6] octahedra forming a linear chain along the c-axis with short M-M distances. Band structure calculations predict semiconducting character with different gaps, which was demonstrated by electrical conductivity measurements and reflected in their different colors. (C) 2014 Elsevier Masson SAS. All rights reserved.