Low-Temperature Synthesis and Electrical Conductivity of (La1–хNdх)0.95Sr0.05F2.95 Nanofluorides with a Tysonite Structure

Abstract

A nanoscale material, which has a tysonite structure (space group \(P\bar {3}c1\)), in the form of a transparent xerogel for the ceramic solid electrolyte (La_1‒хNd_х)_0.95Sr_0.05F_2.95 is obtained by the method of coprecipitation from an aqueous solution of nitrates. The dependences of the unit-cell parameters of the tysonite solid solution (La_1–хNd_х)_0.95Sr_0.05F_2.95 a and c on the composition x are additive (they satisfy Vegard’s rule). With increasing x, the average size of crystalline grains in the coherent scattering region (CSR) of the nanopowders increases from 8–9 to 23.5–26.5 nm. The ionic conductivity of a ceramic sample prepared by cold pressing from a nanopowder of the composition (La_0.5Nd_0.5)_0.95Sr_0.05F_2.95 with a density of ~80% of the theoretical value with the parameters of the trigonal unit cell a = 7.1008 ± 0.0004 Å, c = 7.2796 ± 0.0005 Å, and CSR = 10 ± 0.5 nm is measured. The electrical conductivity of (La_0.5Nd_0.5)_0.95Sr_0.05F_2.95 nanoceramics is 2 × 10^‒3 S/cm at 500 K. The activation energies of ion transfer in the high- and low-temperature regions of electrical conductivity are 0.37 ± 0.04 eV (T > 560 K) and 0.48 ± 0.01 eV (T < 560 K), respectively. The high conductometric characteristics of the nanoceramics make it possible to consider the method of coprecipitation from aqueous solutions as a cost-effective technology in fluoride materials science.