Infrared and far-infrared studies of zinc-compensated -gallates

Single crystals of the fast-ion conductors M -gallate, where M is K, Rb, Ag, or Tl, have been prepared with small amounts of zinc. The zinc doping removes the excess oxygen ions usually found in the conduction plane. Infrared and far-infrared (64000 cm-1) reflectance and transmission spectroscopy have been used to study the lattice dynamics of the zinc-doped spinel blocks and the conducting cations in the more open conduction plane. Comparing these spectra with the infrared and Raman spectra of the undoped and the stoichiometric gallates, we find that the occupation of sites in the conduction plane is different from that of the undoped materials. In addition, the conduction plane in the TlZn-gallate is sufficiently disordered to violate the exclusion principle. No systematic changes were seen in the spinel block lattice modes with the addition of the zinc or the increased cation density which results. © 1984 The American Physical Society.