Moving discommensurations interacting with diffusing impurities

Abstract

We present an analytical description of the interaction between moving discommensurations and diffusing impurities for a realistic form of the impurity-discommensuration interaction energy. This interaction energy is derived within the framework of the modified sine-Gordon model with either misfit impurities (coupling to the gradient of the order parameter) or elastic-modulus impurities (coupling directly to the order parameter). This interaction potential is then employed in calculating the steady-state impurity concentration profile about the moving discommensuration for arbitrary discommensuration velocity and impurity diffusivity. The impurities provide a drag force on the moving discommensuration, which may lead to hysteresis in the relation between the applied force and the discomrnensuration velocity. Analytic results for the onset of hysteresis, as well as for the velocities and forces delimiting the hysteretic regime, are presented. Finally, we apply these results to charge-density waves, ferroelectric domain walls, and grain boundaries.

Influence of Mechanical Stress on the Birefringence Properties of (N(CH3)4)2ZnCl4Crystals

“…The Values Fpi n found in thi8 paper are in agreement with those obtained in [7] equal to 10 -8 Ν for Ba2Νa• Νb5O15 crystals.…”

“…sults obtained in this paper illustrate a set of hysteresis force-velocity dependences for description of soliton motion under mechanical field influence. Numerical values of Fpi n are in agreement with the theoretical estimation [7]. We suppose analogous behaviour for other IC crystals.…”

“…T h e s o -c a l l e d " v i s c o u s " i n t e r a c t i o n manifests itself if the velocities of the IC-stucture motion and defect diffusion become close and the optimum conditions for soliton-defect interaction arise [6]. The force-velocity dependence describing soliton motion [7] acquires a hysteresis character at "viscous" interaction.…”

Manifestation of a Coexistence of the Long-Periodic Phase with the Incommensurate Phase

“…As one can see, at the absence of the electric field the yo, value smoothly varies with temperature and shows inessential anomalous changes. Electric field of strength E =10 4 V/m applied to the sample results in an anomalous temperature behaviour of φa . The optical indicatrix rotation (Fig.…”

“…It was shown that antipolarised regions disappear under influence of electric field and left the vestige, which serves as a germ at field removal. This vestige may be considered as residual defects concentration around soliton [4], that actually causes DDW existence in the crystal. DDW period coincides with the incommensurate structure period at the field absence.…”