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Electrogyration effect in lead germanate crystal family.
1. Electrogyration in the solid solutions based on lead germanate crystals 
1,2Shopa Y., 2Adamenko D., 2Vlokh R., 2Vlokh O.

Shopa Y.1,2, Adamenko D.2, Vlokh R.2 and Vlokh O.2
1Ivan Franko National University of Lviv, 8 Kyrylo and Mefodiy St., 79005 Lviv, Ukraine
2Institute of Physical Optics, 23 Dragomanov St., 79005 Lviv, Ukraine

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Keywords: electrogyration, ferroelectric phase transition, optical activity, lead germanate crystals, phase diagram

PACS: 33.55.Ad, 78.20.Jq, 78.20.Ek, 77.80.-e

Ukr. J. Phys. Opt. 8 197 - 208 
doi: 10.3116/16091833/8/4/197/2007
Received: 01.10.2007

We present the results of studies of electrogyration effect in the solid solutions Pb5(Ge(1-x)Six)3O11 and (Pb(1-x)Bax)5Ge3O11. We show that substitutions of Pb with Ba and Ge with Si do not lead to the changes in electrogyration coefficients, defined in the units of reciprocal electric polarization. At the same time, the main contribution to the changes in electrogyration coefficients, defined in the units of reciprocal electric field strength, is given by critical behaviour of the dielectric permittivity in the vicinity of Curie temperature. It follows from a simple thermodynamic analysis that a hypothetical tricritical point can exist on the x,T-phase diagram for the solid (Pb(1-x)Bax)5Ge3O11 solutions.


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