Kinetic characteristics of the thermal hysteresis in an incommensurate system

The anomalous thermal hysteresis occurring in an incommensurate phase has been investigated in barium sodium niobate. The kinetics of this phenomenon is determined for the first time. We observe relaxation effects with characteristic times of several hours. They are associated with large variations of the heating/cooling plots which are interpretated by assuming that the incommensurate modulation interacts with mobile defects. Similar effects should occur in other real systems with incommensurate phases Etude de l'hysteresis thermique de la birefringence, qui se produit dans la phase incommensurable de Ba 2 NaNb 5 O 15 . Premiere determination de la cinetique de ce phenomene. Observation des effets de relaxation associes a des temps caracteristiques de plusieurs heures, effets qui provoquent de larges variations dans la forme des cycles d'hysteresis. Interpretation par une interaction entre modulation incommensurable et defauts mobiles