Structure, ionic conduction, and giant dielectric properties of mechanochemically synthesized BaSnF4

BaSnF4 fluoride ion conductor has been prepared by mechanochemical milling technique at room temperature. The as-prepared material crystallizes in the cubic fluorite-type structure due to disordering of metal cations. The cubic phase transforms to tetragonal structure by annealing at 460 K. The ionic conductivity of the cubic phase is two to three orders of magnitude lower than the annealed sample. The complex conductivity of the investigated materials has been analyzed by a power-law model in order to extract the hopping rates and the concentration of mobile ions, the parameters that control the overall conduction behavior. The estimated values of the concentration of mobile ions are found to be of the same order, indicating that the conduction process is controlled by the mobility of charge carriers. BaSnF4 has been found to belong to a new class of nonoxidic giant dielectric constant materials with a value of epsilon' similar to 10(5), which is independent of temperature and frequency over wide ranges. It is found that the giant values of the dielectric constant are not due to surface barrier layer capacitance effects at the sample/electrode interface of the material. (C) 2009 American Institute of Physics. [doi:10.1063/1.3234393]