Crystal Structure and Conductivity of the New Superionic Conductors Ag 4Zr 3S 8 and Ag 3.8Sn 3S 8

The new superionic conductors Ag 4Zr 3S 8 and Ag 3.8Sn 3S 8 crystallize both in cubic space groups with lattice parameters a = 10.9427(3) Å ( P4 332, Z = 4, and ρ = 4.87 g cm -3) and a = 10.8013(4) Å ( P4 132, Z = 4, and ρ = 5.39 g cm -3), respectively. These compounds have similar sulfur packing consisting of sulfur octahedra sharing common edges. In both cases the M cations, either Zr or Sn, are located inside the sulfur octahedra (12 d sites). The main crystallographic difference between the two structures is the silver packing. In Ag 4Zr 3S 8 the silver ions are located in three different tetrahedral sites, two of them being partially occupied. For Ag 3.8Sn 3S 8 the silver ions are exclusively situated in statistically occupied octahedral sites (12 d and 4 b sites) giving a rock-salt-type lattice. From the properties point of view, they are both mixed conductors exhibiting a relatively high ionic conductivity. The ionic σ Ag+ and total conductivities were measured from room temperature to 205°C.