E. Hegenbarth

Glasslike behaviour of crystalline solids at low temperatures

Abstract Amorphous solids show at some low temperature properties an universal behaviour, which is caused by localized low energy excitations. Also at crystalline solids glasslike behaviour was found. By measuring thermal and dielectric properties at different kinds of ferroelectrics it is shown, that this behaviour is connected with the phase transition.

The influence of hydrostatic pressure on the phase transition of TSCC

Abstract At TSCC by hydrostatic pressure a shifting of phase transition to higher temperatures was observed. The initial shifting is dTo/dp = 0.097 K/MPa for a monodomain and dTo/dp = 0.125 K/MPa for a multidomain TSCC-crystal. At pressures higher than 300 MPa a nonlinear shifting was found. Above pressures of 420 MPa no phase transition could be detected by dielectric measurments.

The influence of hydrostatic pressure on the phase transitions of some

At some ferroelectrics the influence of hydrostatic pressure on the phase transition was investigated. The results are discussed mainly on the basis of thermodynamic considerations. A relation for the nonlinear pressure shifting at low temperatures for ferroelectrics with a phase transition of first or second order is given. The influence of hydrostatic pressure on ferroelectrics with diffuse phase transitions is discussed.

Thermal conductivity of some ferroelectrics at low temperatures

Abstract The thermal conductivity of different ferroelectrics at low temperatures is discussed. It is pointed out that ferroelectrics with pure displacive transitions show a different behaviour than ferroelectrics where proton tunneling is important at the phase transition. Also effects of anisotropy and effects of deuteration are discussed. It is shown, that from the analysis of thermal conductivity important informations about diferent scattering processes can be obtained.

The different influence of hydrostatic pressure to the glassy dielectric behavior of ferroelectrics with diffuse and sharp phase transition

Abstract Investigations of different ferroelectrics under high hydrostatic pressure at low temperatures show that the dielectric loss maximum as it appears at many glasses can be influenced by pressure. At ferroelectrics with diffuse phase transition the activation energy of the excitations responsible for the loss maximum decreases by pressure while their number increases. In contrast at (Ba, Sr) TiO3 solid solutions with sharp phase transition the activation energy is not markedly changed by pressure, but the number of excitations decreases up to the critical pressure where a sudden change of the activation energy occurs.

Dielectric long-time relaxation after reducing hydrostatic pressure at ferroelectrics with diffuse phase transition

Abstract 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.

Thermal conductivity of Strontium-Barium-Niobat under high pressure and at low temperatures

Abstract A new method to meassure thermal conductivity at lot; temperature and under high pressure is developed to investigate ferroelectric materials. Results at Strontium-Barium-Niobat (SBS) shah; the influence of the pressure to the glasslike behavior. Also a strong anisotropie of thermal conductivity is detected at this substance.

Thermal conductivity measurements on (Pb1-xBax)(Sc0.5Nb0.5)O3

In the paper are presented thermal conductivity measurements on low temperature behaviour of (Pb1-xBax)(Sc0.5Nb0.5)O3 samples in the temperature range from 200 mK up to 70 K. The barium ions cause a decrease of the thermal conductivity which is not saturated at x = 0.06. This effect cannot be understood as point defect scattering. The additional disorder of the material due to the barium ions leads to a modification of the soft potentials which are responsible for the glassy low temperature behaviour of (Pb1-xBax)(Sc0.5Nb0.5)O3.

Thermal conductivity of LI-TL-tartrate single crystals at low temperatures

On a single crystal of Li-Tl-Tartrate the thermal conductivity in the temperature range of 4. 2-80 K was measured. At the phase transition a distinct change of slope was observed. The anisotropy of the thermal conductivity between the a- and the b-direction of the crystal is very high. This behaviour is caused by a strong scattering of phonons at protons.

Ultrasonic investigations of solid solutions of SrTiO3 at low temperatures

By the impulse-superposition method the sound velocity of polycrystalline (Ax, Sr1-x)TiO3 solid solutions are measured, mainly in the temperature range of 4. 2-300 K. Some anomalies at the velocity are observed, which are connected with the structural phase transition in pure SrTiO3 at 105 K and ferroelectric phase transitions, which are induced by substitution of different cations in the lattice of SrTiO3. The results are compared with measurements of the dielectric constant. The influence of different concentrations x on the phase transition and the kind of phase transition are discussed.