Induced displacive transition in heterogeneous materials

Abstract

Abstract.A model of heterogeneous, composite material is introduced, consisting of randomly distributed identical structural micro-domains endowed with electric charges or dipoles. Two cases are presented, one corresponding to a tightly packed (dense) material, another corresponding to highly-dispersed, small domains. The polarizability is computed in both cases, under the action of an external uniform electric field oscillating in time (a quasi-stationary field), and it is related to the displacement of the micro-domains from their positions of local equilibrium (translations or rotations). It is shown that the polarizability (or electric susceptibility) can exhibit characteristic (resonance) frequencies in the radio-frequency range and, even for moderate external fields, the material can undergo a displacive transition (similar to a ferroelectric transition), governed by non-linearities in the interaction energy of the micro-domains. The shift in the characteristic frequencies of the polarizability is estimated, as caused by the displacive modification.

Semiclassical treatment for molecular rotation spectra in high electric fields

“…The spontaneous polarization caused by the dipolar interaction as described above may appear in polarization domains, randomly distributed in polar matter (pyroelectrics, ferroelectrics), or in granular matter, where charges may accumulate at the interfaces. [35]- [41] This is known as the Maxwell-Wagner-Sillars effect (an average over the angle α should then be taken in the absorbed power). In the latter case the distance between the dipoles is much larger than the atomic distances and, consequently, the characteristic frequency ω 0 is much lower; for instance, for a distance a = 1µm (10 4 Å) we get a frequency ω 0 ≃ 10MHz.…”