What is it about?
New realizations of memory effects Iinked with defect density waves have been established by X-ray investigations of Ag3AsS3, SC(NH2)2and TMA- ZnCIJcrystals.Theyinvolvethe presence of additional wave modulation with temperature independent wave vector, interference of the normal and additional waves, the presence of the new intermediate state in the temperature region of two-phase state, the reverse hysteresis at the N<->IC phase transition.
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Why is it important?
Many crystals with.incommensuratephases exhibit memory effects, which consist of the appearance of thermal anomalies in physical properties after a prolonged hold of the crystal at a constant temperature To inside the incommensurate phase region. 'The effects are linked with an interaction of structural modulations with mobile defects in the crystal. It is assumed that during the hold of the sample at constant temperature this interaction leads to a periodic change in the concentration of the defects, a "defect-density wave", with a period equal to the period of the structural modulations at To . During subsequent scans of the crystal temperature near T,, the defect density wave "captures" the structural modulations, thereby causing anomalies in physical properties.*In the present work we report the structural evidence for the existence of defect-density waves and some manifestations of memory effects linked with them.
Perspectives
We explain this result by interaction of DDWs which are produced at later stage of the sample cooling with consequent wave modulations. The difference between the wave vectors of low temperature DDWs with high temperature modulations will destroy the latters thus decreasing the reverse phase transition temperature. The lower heating temperature the greater difference in the wave vectors and hence the lower the temperature of the destruction.
Dr Bagautdin Bagautdinov
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This page is a summary of: Defect density waves and special realizations of memory effects in crystals with incommensurate phases, Ferroelectrics, September 1996, Taylor & Francis,
DOI: 10.1080/00150199608210525.
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