Glasslike behaviour of ferroelectrics at low temperatures

Amorphous solids show in some low temperature properties, a nearly universal behaviour which is caused by localized low energy excitations. By measuring heat capacity and thermal conductivity it is shown that this behaviour can be observed also in ferroelectric substances. It is found that glasslike behaviour is most pronounced in relaxor ferroelectrics. Only in these substances can the localized states be influenced by an electric field and by hydrostatic pressure. From our investigations one can conclude that, for glasslike behaviour at crystalline substances, a structural phase transition is a necessary condition. In the case where phase transition temperature Tc and Debye-temperature ΘD of a substance are nearly equal, a large number of localized states are generated and properties similar to those in pure amorphous solids can be observed.

Keywords:

• Thermal conductivity
• ferroelectrics
• very low temperature