Influence of a Frozen Defects Density Wave on the Incommensurate Modulation in Barium Sodium Niobate

Abstract

It is shown by means of an X-ray scattering technique that the memory effect in incommensurate Barium Sodium Niobate is associated to the freezing of the modulation wave vector over a wide range of temperature. This result is consistent with the existence of defects induced locked phases. In addition two unexpected phenomena have been observed; a splitting of the modulation into two components and a specific temperature evolution of the ferroelastic domains pattern which can be related to the behaviour of the modulation. The possible origins of these phenomena are discussed.