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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.

The complex dielectric constant of PSN and SBN was measured below 1K in the frequency range between 1 and 200kHz. The observed behaviour of these ferroelectric crystalline materials is known to be typically for amorphous and disordered materials.

Investigations at 18 different ferroelectrics and 2 quantum paraelectrics indicate that materials with a structural phase transition show a typical glassy behavior at low temperatures if the structural phase transition temperature Tc is nearly equal to the Debye temperature θD. In this case, the mean energetical density [Pbar] of localized states responsible for the glassy properties has a maximum. The ratio Tc /θD has a strong influence on the generation of focalized states in different substances with a structural phase transition.

The thermal expansion coefficient of solids gives useful information about the anharmonicity of the vibrations in the asymetric binding potential and about the nature of phase transitions. Therefore it was built a capacitive dilatometer for the low temperature region, because this type provides the highest sensitivity of all known measuring methods of thermal expansion.1

Measurements of thermal conductivity, specific heat, and dielectric properties of an epoxy resin after electron, gamma, fast-neutron, and thermal-neutron irradiation are presented. The experimental results show the influence of the different types of radiation on the typical amorphous behaviour of the thermal properties. The H2-permeation rate for two types of carbon-fibre-reinforced plastics are presented.

Investigations of dielectric absorption at low temperatures show that the localized glassy states in different ferroelectrics can be sup-pressed and generated by hydrostatic pressure and/ or an electric field. This behavior is connected with a different change of the shape of the double-well potential of these states.

It was found a non-exponential time dependence of the complex dielectric constant after reducing hydrostatic pressure (p ≲ 1 GPa) at different ferroelectrics with diffuse phase transition. The results show the peculiarity that the dielectric relaxation becomes stronger after a critical time. It is suggested that this effect is connected with localized states responsible for the glasslike properties of these substances.

Experimental investigations of the glassy dielectric absorption maximum at low temperatures between 10 K ≤ TM ≤ 100 K at 14 different ferroelectrics are presented. From these investigations one can conclude that a connection between localized states, which cause this absorption maximum, and the structural phase transition ferroelectric-paraelectric exists.