CRYSTAL-STRUCTURE AND CONDUCTIVITY OF THE NEW SUPERIONIC CONDUCTORS AG4ZR3S8 AND AG3.8SN3S8

The new superionic conductors Ag4Zr3S8 and Ag3.8Sn3S8 crystallize both in cubic space groups with lattice parameters a 10.9427(3) Angstrom ( P4(3)32, Z = 4, and rho = 4.87 g cm(-3)) and a = 10.8013(4) Angstrom ( P4(1)32, Z = 4, and rho = 5.39 g cm(-3)), respectively. These compound s have similar sulfur packing consisting of sulfur octahedra sharing c ommon edges. In both cases the M cations, either Zr or Sn, are located inside the sulfur octahedra (12d sites). The main crystallographic di fference between the two structures is the silver packing. In Ag4Zr3S8 the silver ions are located in three different tetrahedral sites, two of them being partially occupied. For Ag3.8Sn3S8 the silver ions are exclusively situated in statistically occupied octahedral sites (12d a nd 4b sites) giving a rock-salt-type lattice. From the properties poin t of view, they are both mixed conductors exhibiting a relatively high ionic conductivity. The ionic sigma(Ag+) and total conductivities wer e measured from room temperature to 205 degrees C. (C) 1995 Academic P ress, Inc.