Activation energy of ion motion in the nanodimensional lattice of LaF₃ superionic conductor

Abstract

Quantum chemistry calculations of the intracrystalline potential relief in the nanolattice of LaF₃ superionic crystal that contains 1200 ions and measures 3.5 × 2.0 × 2.2 nm along the x, y, and z axis, respectively, have been performed. Using the MOPAC 2012 program package, the potential relief profile has been simulated in the central part of the nanolattice for an elementary act of disordering in the lowest melting sublattice of F₁ ions. It has been found that the height E _m of barriers that prevent the motion of F₁ in the dielectric phase of LaF₃ crystal equals 0.37 eV and decreases to 0.15 eV in the superionic state. In addition, activation energy E _a of F₁ sublattice disordering in the dielectric and superionic states is equal to 0.16 and 0.04 eV, respectively. The profiles of the potential relief calculated on the xy and xz faces of the LaF₃ 3D nanolattice for the case when an F₁ ion moves along the x crystal axis in the dielectric state are presented. The corresponding energy barriers are 1.5–2.0 times lower than those at the center of the LaF₃ nanlattice.