Experimental investigation and modelling of the Na+ mobility in NaLnTiO4 (Ln = La, Nd) ceramics

In NaLnTiO4 (Ln = La, Nd) layered perovskite-like compounds, the mobility of sodium ions was studied using impedance spectroscopy and simulated by the molecular dynamics approach. NaLnTiO4 was prepared via a high-temperature solid-state reaction with final annealing at 900 °С. The conductivity was measured using the complex impedance technique between 1 MHz and 100 Hz in the temperature range of 523-923 K. Using the DFT (Density Functional Theory) method, the charges of atoms in the crystal structure were calculated and applied to simulate the sodium atom mobility in NaNdTiO4 and NaLaTiO4 crystals using classical molecular dynamics in the temperature range of 523-923 K. Based on these calculations, the dependence of the diffusion coefficients of sodium atoms on temperature was studied. The mobility of sodium ions in NaLaTiO4 is demonstrated to be higher than that in NaNdTiO4 because of the more ionic characteristic of its bonds.