Mechanochemical Synthesis of Nanopowders and Ionic Conductivity of Nanoceramics of the (Pb0.67Cd0.33)0.825Sr0.175F2 Fluorite Solid Solution

Abstract

We have studied structural and ion-conducting properties of a nanoceramic (Pb_0.67Cd_0.33)_0.825Sr_0.175F₂ solid solution (CaF₂ structure, sp. gr. \(Fm\bar {3}m\)). Nanocrystalline powders were prepared by mechanochemical synthesis using two types of starting mixtures. One mixture was prepared using melted PbF₂, CdF₂, and SrF₂ individual fluorides, and the other, using a prefused Pb_0.67Cd_0.33F₂ solid solution and SrF₂. The way in which the starting mixture was prepared was found to have no effect on the formation and properties of the ternary solid solution. The lattice parameter of the (Pb_0.67Cd_0.33)_0.825Sr_0.175F₂ solid solution was determined to be a = 5.778 and 5.772 Å in the case of the former and latter starting mixtures, respectively. Using X-ray diffraction data, the average crystallite size of the nanopowders was estimated at several tens of nanometers. Nanoceramics were prepared by cold-pressing the powders. Their density was 80% of the X-ray density of the solid solution (6.89 g/cm³). Annealing at 500°C for 2 h increased the density of the ceramics to 90%. The ionic conductivity σ_dc of the as-prepared and annealed nanoceramics was determined to be 2.5 × 10⁻⁶ and 1.2 × 10⁻⁵ S/cm, respectively. The σ_dc of the annealed nanoceramic is 20% lower than that of a single crystal with the same composition.