Time evolution of an incommensurate structure of Rb₂ZnCl₄ in uniaxial mechanical stresses

Institute of Crystallography, Russian Acad.Sci., 117333, Moscow, Leninsky pr., 59, Russia

In the region of ferroelectric phase transition of Rb₂ZnCl₄ crystals, the relaxation of incommensurate (soliton) structure (IS) transferred abruptly to a nonequilibrium state with uniaxial mechanical stress G has been studied. The evolution of IS was recorded by recording changes in the dielectric constant E along the Y axis.

The main results are as follows. When the initial deviation from equilibrium is small (G ~ 5 kg/cm²), the constant E starts to change with time t (t ~ 10 min) logarithmically in accord with the interpretation that the relaxation of the inhomogeneous system is a thermally activated process governed by metastability effects. When the initial state of IS is far from equilibrium (G >> 5 kg/cm²), IS relaxes substantially faster and at the beginning of relaxation there appear peculiarities typical for the switching of ferroelectric and magnetic domain structures, i.e. the farther is the initial IS state from equilibrium, the faster IS goes through the certain states. As a result the E, t-curves corresponding to different initial states intersect and further they follow again the time logarithmic law. Possible relaxation mechanisms are discussed. Some characteristics of the crystal are estimated.