Self-organization of particles in the superionic phase of lanthanum trifluoride

When a laser beam ($\lambda$ = 396.3 nm) propagates through a nonuniformly heated superionic LaF$_3$ crystal in the direction of lattice constant c, alternating bright and dark fringes arise on the screen. The fringes run from the warmer face to the colder one. The number and width of the fringes are found to depend on the temperature gradient in the crystal: the smaller (greater) the temperature difference between the faces, the smaller (greater) the number of moving fringes. It is the author’s opinion that this effect is due to the wave transfer of applied heat and reflects the self-organization and collective displacements of the ions of the “quasi-liquid” sublattice in a nonuniform temperature field. A qualitative model of heat wave transfer in the LaF$_3$ superionic phase is suggested.