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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.

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Abstract--The migration of ledges in a semicoherent ct/fl interface is considered to participate in solid-state transformations driven by diffusion. The advance of the ledge and/or the progress of the transformation can require the climb of misfit dislocations both in the ledge and in its path. The creation or annihilation of vacancies required for the transformation and the ledge advance is provided by a combination of three vacancy sources or sinks: (a) the net vacancy flux to/from the interface resulting from the difference in lattice plane shift (Kirkendall effect) within the two contacting phases, (b) the climb of misfit dislocations from the interface into the bulk of the ct and fl phases, and (c) the climb of misorientation dislocations within the interface. Thus, the dynamic action of the interface during the phase transformation would include: (i) climb of misfit dislocations out of the interface, with ensuing dissociation into glissile dislocations which resupply the interface by return glide, and (ii) climb of misorientation dislocations in the interface necessitating a continuing arrival of such dislocations from sources in the bulk or in the interface.R6sum6---La migration d'une marche d'un interface ~/fl semicoh6rent intervient darts les transformations solide-solide control6es par la diffusion. Le d6placement d'une marche et/ou le d6placement de l'interface n6cessite la mont6e des dislocations interfaciales. Darts l'hypoth6se de la conservation du nombre total de noeuds de r6seaux, la cr6ation ou l'annihilation des lacunes n6cessaires A la transformation et au d6placement des marches est la r6sultante de trois sources ou puits de lacunes d'origine diff6rente: (a) la cr6ation ou l'annihilation de lacunes par l'interface compensant la diff6rence de d6placement des plans atomiques (Effet Kirkenda11) au sein des deux phases, (b) la mont6e des dislocations de vernier de l'interface vers les phases ct et/~, et (c) la mont6e des dislocations de d6sorientation dans rinterface. De ce fait, le r61e de l'interface au cours d'une transformation de phase dolt tenir compte: (i) de la mont6e des dislocations de verniers hors de l'interface, la dissociation de ces dislocations, g6n6ralement sessiles, en dislocations glissiles permettant leur retour vers l'interface par glissement, et (ii) de la mont~ des dislocations de d6sorientation dans le plan de l'interface, ce qui n6eessite la pr6sence d'une source permettant le renouvellement continu de ces dislocations.