Ferroelectric properties of the LaF$_3$ superionic conductor nanocluster

We report on the results of quantum-chemical calculation of the lattice energy in a LaF$_3$ superionic crystal of size 3.5 $\times$ 2.0 $\times$ 2.2 nm that contains 1200 ions with different structural configurations of fluorine ions. It has been shown that the most energetically disadvantageous configurations of fluorine ions correspond to arbitrarily (randomly) disordered nanolattices in the case when fluorine ions of all three types (F$_1$, F$_2$, and F$_3$) participate in their melting. It has been found that unidirectionally disordered nanolattices that contain a large number of defect dipoles of the anion vacancy–interstitial fluorine atom type with parallel dipole moments is energetically more advantageous than nanolattices with randomly disordered structure. It has been proposed that the electric field produced by a large number of parallel defect dipoles is formed in disordered LaF$_3$ nanolattices even at room temperatures. This makes it possible to classify microscopically small LaF$_3$ crystallites as promising functional materials that can be used, e.g., in modern solid-state technologies.