Superionic Ag+ Conductor Ag17(CO3)3I11

A new superionic Ag+ conductor with a nominal composition Ag-17(CO3)(3)I-11 (11AgI-3Ag(2)CO(3)) was found in the AgI-Ag2CO3 system. The conductor, which was formed at temperatures from 100 to 170 degrees C, is a metastable phase that gradually decomposes into AgI and Ag-10 (CO3)I-4 over a period of a few weeks at room temperature (RT). A Ag+ ionic conductivity of 0.16 S/cm was measured at RT, and an activation energy of 0.33 eV was evaluated in the temperature range from -9 to 19 degrees C. Single-crystal X-ray analysis revealed that Ag-27(CO3)(3)I-11 crystallized in a rhombohedral unit cell with hexagonal parameters of a = 15.8831(6) angstrom and c = 30.0730(13) angstrom at -183 degrees C and space group R3c. The Ag atoms were distributed over 53 sites in the asymmetry unit, with a maximum occupancy of 0.33(8). The continuous distribution of the partially occupied Ag sites was associated with the conduction paths of the Ag+ ions in the structure.