Quasi-localized vibrations and phonon damping in glasses

There is ample evidence both from computer simulation and experiments that the structural disorder characterizing glasses and amorphous materials leads to quasi-localized vibrations (QLVs). The effect of these modes on low temperature properties such as heat capacity and conduction or tunnelling can be calculated in the framework of the soft potential model. Recently it has been shown that this concept can be extended to describe the boson peak (BP). By interaction, the density of states of the QLVs is changed to a characteristic shape corresponding to the boson peak in inelastic scattering. The QLVs interact with the sound waves and dampen them. We show that resonant scattering between QLVs and sound waves can describe the strong damping observed experimentally.     

Evolution and Operating Experiences with Different Drop‐On‐Demand Systems

Summary: We describe the development of different drop‐on‐demand systems particularly for applications for the liquid handling of biopolymers. Different designs of drop‐on‐demand systems developed by the authors are described. Experiments with these systems show the applicability for pipetting different liquids with different properties. Commercially available systems are also tested. A comparison of the different approaches leads to a discussion of the best fields of application of the different approaches or, alternatively, to the potential further development of the drop‐on‐demand technologies.

Principle setup of the print heads.     

Quantum tunneling of light particles in metals

The motion of a particle in a metallic crystal is studied for low temperatures where transitions between adjacent interstitial sites are caused by quantum tunneling. The influence of electrons and phonons on the hopping rate is taken into account by means of a functional integral method. The electronic influence may effectively be described by Ohmic damping which dominates the low temperature behavior of the defect motion. When subsequent tunneling transitions are statistically independent, the diffusion constant is found to obey a power law, D∼T^2K−1, where K depends on the defect-electron interaction. This power law is limited at low temperatures by the effects of phonon excitations. Near the transition between electron and phonon dominated behavior the diffusion constant has a minimum where the precise temperature dependence of the rate depends not only on phonon spectra but also on the processes limiting phonon lifetimes.     

Proton conductivity in silica gels

Commercial silica gel drying pearls were used in impedance measurements between ambient temperature and 300 °C in dry and humid atmospheres. A pronounced difference was seen supporting previous conclusions that proton conduction was operative in these amorphous samples. The same conclusion was reached on the basis of a fuel cell experiment at ambient temperature. A Nernst voltage close to the theoretical one was observed. Mechanical tests were carried out with silica gel plates made from the above material. Such plates displayed in the bending mode a time-dependent anelastic relaxation, i.e., a Gorsky effect, which arose from the long-range diffusion of protonic defects from the compressed to the dilated part of the plate. The chemical diffusivity and the density of the protonic defects could be determined. The same Gorsky effect may be expected in crystalline proton conductors, and also in Li-containing ceramics.     

Measurements and evaluation of the hydrogen uptake in Yb-doped strontium cerate

The water uptake of SrCe_0.95Yb_0.05O_3-α was studied by in situ thermogravimetry. At different temperatures, mass changes due to variations of water vapour pressure were recorded; from these, the remaining vacancy concentrations were calculated. Further analysis in terms of the equilibrium constant was carried out without any assumptions on the initial vacancy concentration. The requirement of an ideal solution behaviour led us to the introduction of an effective vacancy concentration differing from the nominal one. At last, a universal mastercurve is presented showing the fraction of vacancies occupied as a function of a normalized pressure. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

The local displacement field around Co and Nb solutes in ω-phase forming bcc-Zr at high temperatures

In order to determine the displacement field around Co and Nb solutes in high temperature bcc-Zr the diffuse scattering intensity was measured in Zr_0.985Co_0.015 and Zr_0.92Nb_0.08. Strong diffuse intensities were found in the (110) and in the (001) reciprocal planes. The comparison of these results with model calculations shows that Co as well as Nb atoms cause radial symmetric displacement fields in the high temperature bcc phase of Zr. -phase like displacements around these defects, on the other hand, can explain the measured diffuse intensities less well. It is concluded, that the resulting displacement field is a superposition of all displacements for which low energy phonons exist. These low energy phonons are related to the martensitic transitions of the bcc structure to the hcp and -structure.