Synthesis, electrical conductivity, and crystal structure of Cu4Sn7S16 and structure refinement of Cu2SnS3

Single crystals of Cu4Sn7S16 and Cu2SnS3 were prepared by the conventional solid state reaction method. Their crystal structures were determined from single-crystal X-rag data. Cu4Sn7S16 is off a new structure type with rhombohedral symmetry: R-3m, a = 7.372(1), c = 36.010(7) Angstrom, Z = 3, R = 0.018 for 522 structure factors and 36 variable parameters. Its crystal structure may be described as a defect variant off the spinel-type, In the unit cell, 3/4 of the tetrahedral sites and 1/8 of the octahedral sites are occupied by Cu+, while 7/8 Of the octahedral sites are occupied by Sn4+ ions. The compound can therefore be formulated as (Cu(0.75)square(0.25))(Sn1.75Cu0.25)S-4. Cu2SnS3 has the unit cell formula Cu-2.665(7)Sn-1.335(7)S-4 (Z = 2) and it is isotypic with the tetragonal stannite [Cu-2(Fe, Zn)SnS4] structure: I-42m, a = 5.413(1), c = 10.824(1) Angstrom, R = 0.030 for 281 reflections and 16 variables. In the case of Cu2SnS3, the positions of the Cu and Sn atoms of stannite: are occupied by the composite atoms M1 [43.6(2) at.% Sn + 56.4(2) at.% Cu] and M2 [46.3(3) at.% Sn + 53.7(3) at.% Cu], respectively, while those of the: (Fe, Zn) atoms are replaced by only Cu atoms, Electrical conductivity measurements confirm the expected semiconducting behavior of Cu4Sn7S16, and XPS analysis reveals the presence of only Cu+ in Cu4Sn7S16. (C) 1998 Academic Press.