Effect of Heat Treatment in a СF4 Atmosphere on the Ion-Conductive Properties of Hot-Pressed 95 mol % CeF3 × 5 mol % SrF2 Ceramics

Abstract

X-ray and electrophysical investigations of ceramics with a charge composition 95 mol % CeF₃ × 5 mol % SrF₂ synthesized by hot pressing of CeF₃ and SrF₂ powders (300 MPa, 900°С, 20 min) in vacuum and the same ceramics annealed in a fluorinating atmosphere (CF₄, 1000°С, 180 min) have been carried out. The initial two-phase ceramics consists of the tysonite phase (a = 7.130(1) Å, c = 7.295(1) Å) and up to 2 wt % of fluorite impurity phase (a = 5.77(1) Å). The ionic conductivity of the initial ceramics is σ_dc = 2.8 × 10^–4 S/cm at room temperature. Heat treatment of the ceramics in a fluorinating atmosphere eliminates the fluorite phase. After the annealing, the ceramics becomes single-phase and turns to the Ce_1 − ySr_yF_3 − y tysonite solid solution. The σ_dc value of the annealed ceramics with the nominal composition Ce_0.95Sr_0.05F_2.95 increases by a factor of ∼1.5 and coincides with the σ_dc value for a single crystal of the same composition.