Dipole-glass state

The comparison of Figs. 3.23 and 3.24 shows that the films thickness decrease reveals the features similar to those at the increase of distribution function width. This means that the decrease of film thickness may be considered as equivalent to the disordering of the system. The reason for that is that the fluctuations due to film thickness decrease have the same nature as those at the system disordering. In other words, in thinner films of relaxor ferroelectrics, the part of long range order decreases so that dipole glass state may appear in free-standing films. The complement state in such situation may be the electret-like one with remnant polarization induced by built-in field. Latter state is more profitable in the thinnest possible films with thickness less than some critical value. 

Similar results have been reported for Eu3+ in glasses (J4) germanate glasses where the Eu3+ c.t. band is situated at 38462 cm i show a more intense forced-electric-dipole emission than phosphate glasses, where the c.t. band lies at 49020 cm i. These excimples illustrate the influence of the c.t. state upon the Eu3+ 4/- 4/ emission. 

Classical relaxors [22,23] are perovskite soUd solutions like PbMgi/3Nb2/303 (PMN), which exhibit both site and charge disorder resulting in random fields in addition to random bonds. In contrast to dipolar glasses where the elementary dipole moments exist on the atomic scale, the relaxor state is characterized by the presence of polar clusters of nanometric size. The dynamical properties of relaxor ferroelectrics are determined by the presence of these polar nanoclusters [24]. PMN remains cubic to the lowest temperatures measured. One expects that the disorder -type dynamics found in the cubic phase of BaTiOs, characterized by two timescales, is somehow translated into the... 

In Section 4, we have examined, from a fundamental point of view, how temperature and cure affect the dielectric properties of thermosetting resins. The principal conclusions of that study were (1) that conductivity (or its reciprocal, resistivity) is perhaps the most useful overall probe of cure state, (2) that dipolar relaxations are associated with the glass transition (i.e., with vitrification), (3) that correlations between viscosity and both resistivity and dipole relaxation time are expected early in cure, but will disappear as gelation is approached, and (4) that the relaxed permittivity follows chemical changes during cure but is cumbersome to use quantitatively. 

There are many questions about relaxors. Are they similar to dipolar glasses where elementary dipoles exist on the atomic scale or is the relaxor state indeed characterized by the presence of nanosized polar cluster of variable sizes and orientations. 

Abstract Modern solid state nuclear magnetic resonance presents new powerful opportunities for the elucidation of medium range order in glasses in the sub-nanometer region. In contrast to standard chemical shift spectroscopy, the strategy presented here is based on the precise measurement and quantitative analysis of internuclear magnetic dipole-dipole interactions, which can be related to distance information in a straightforward manner. The... 

Keywords Dipolar solid state NMR Medium-range structure Oxide glasses Internuclear magnetic dipole-dipole interactions... 

---