Dielectric anomalies

Lattice dimerization in the course of the spin-Peierls-like transition leads to the appearance of new optically active modes folded from a boundary of the Brillouin zone to its center. Charge ordering results in a dielectric anomaly observable in the far-infrared spectral region. 

YC1O3 shows canted antiferromagnetism (7n = 140 K) and a dielectric anomaly like a ferroelectric at 473 K47 (Fig. 8). Dielectric hysteresis in YCrCb is like in leaky dielectrics with a small polarization... 

Earlier experiments [400,401] (see also Refs. 402 and 403) showed that hydrated colloidal particles are characterized by polarization whose nature is determined by spontaneous orientation of the polar molecules of water on the surface of particles leading to formation of the giant momentum P. The energy advantage of formation of P is shown in Ref. 404, which is in agreement with a detailed study of the dielectric anomalies in thin water layers conducted in Ref. 405. Spontaneous polarization of the monolayers of polar molecules is theoretically substantiated in Refs. [406,407]. 

Since nonpolar molecules do not have constant polarizability, what can we say about their dielectric anomaly The difference in the pair and triplet polarizabilities in real noble-gas molecules and our model molecules can be summarized in terms of S2 by saying that we would expect a similar sort of integral to provide a reasonable approximation to S2 at p, but with an 02(r) quite different from that given by (4.71b). In the case of helium, for example, where the linearityof Sj in p suggests that three-body effects are of less importance than in argon, Sj might be reasonably approximated at p by the expression... 

Pozhidayev, E.P., Blinov, L.M., Beresnev, L.A., Belyayev, V.V. The dielectric anomaly near the transition from the smectic A to smectic C phase and visco-elastic properties of ferroelectric liquid crystals. Mol. Cryst. Liq. Cryst. 124, 359-377 (1985)... 

The methanol compound has a phase transition at 66 K for a =0.97 as shown by a sharp heat capacity anomaly [14]. The temperature of the peak decreased as the occupancy decreased. This provides a piece of evidence which proves that the phase transition is caused by the interaction between the guest molecules. Dielectric anomaly occurs also at the transition, showing that orientation of the guest molecules changes at the transition temperature (see Fig. 3) By the use of proton, deuteron and carbon 13 NMR, it was found [15] that the orientation of the guest molecule is more complicated than had originally been believed to be [14]. The new model was supported by X-ray crystallography [16]. 

BaMnFit (LB Number 26A-2). This crystal exhibits a dielectric anomaly at about 242 K (Fig. 4.5-49). The coercive field is very large. The crystal is antiferromagnetic below 25 K (Fig. 4.5-50). The dielectric constant varies depending upon the magnetic field at low temperatures (Fig. 4.5-51). 

Mason WP (ed) (1964) Physical acoustics. Academic, New York, NY Nelson DF (1979) Electric, optic and acoustic interactions in dielectrics. Wiley, New York, NY Thomson W (Lord Kelvin) (1878) On the piezoelectric property of quartz. Phil Mag 5 4 Tichy J, Gautschi G (1980) Piezoelektrische Messtechnik. Springer, Heidelberg Toledano P, Dmitriev V (1996) Reconstructive phase transitions. World Scientific, Singapore Valasek J (1920) Piezoelectric and allied phenomena in Rochelle salt. Phys Rev 15 537-538 Valasek J (1921) Piezoelectricity and allied phenomena in Rochelle salt. Phys Rev 17 475-481 Valasek J (1922) Piezo-electric activity of Rochelle salt under various conditions. Phys Rev 19 478 Valasek J (1924) Dielectric anomalies in Rochelle salt crystals. Phys Rev 24 560 Voigt W (1890) General theory of the piezo- and pyroelectric properties of crystals. Abh Gott 36 1-99... 

Valasek J (1924) Dielectric anomalies in Rochelle salt crystals. Phys Rev 24 560-568 Valasek J (1971) The early history of ferroelectricity. Ferroelectrics 2 239-244 Zheludev IS (1975) Elektrische Kristalle. Akademie, Berlin... 

Tauer, K. J. and Lipscomb, W. N. (1952). On the crystal structures, residual entropy and dielectric anomaly of methanol. Acta Crystallogr., 5, 606-612. 

---