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Journal of Physical Studies 21(1/2), Article 1704 [12 pages] (2017)
DOI: https://doi.org/10.30970/jps.21.1704 THE INFLUENCE OF UNIAXIAL PRESSURES ON THERMODYNAMIC PROPERTIES OF THE GPI FERROELECTRICI. R. Zachek1, R. R. Levitskii2, A. S. Vdovych2
1Lviv Polytechnic National University |
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An attempt to ascertain the mechanism of phase transition in GPI type crystals is the main motivation for our investigations, including for the present study. The main task of the present work is elaboration a pseudo-spin model for this type crystal capable of describing temperature, field and pressure dependences of thermodynamic and dynamic properties of such crystals observed experimentally.
We use the model of the GPI crystal modified by taking into account the piezoelectric coupling between ordering structure elements and the strains $\varepsilon_i$, $\varepsilon_j$ for the investigation of the effects, that appear under uniaxial pressures. Thermodynamic potential is calculated within two particle cluster approximation for short-range interactions and mean field approximation for long-range interactions. We obtained the system of equations for order parameters and strains using thermodynamic equilibrium equations. The components of the polarization vector and static dielectric permittivity tensor of mechanically clamped crystal, expressions for isothermal coefficients of piezoelectric stress and relations for constants of piezoelectric stress of GPI type crystals are calculated on basis of these equations. The temperature and pressure dependences of the obtained physical properties of such crystals are calculated and investigated in detail at the proper choice of the model parameters.
Character of influence of uniaxial pressures on the strains, polarization and inverse static dielectric permittivity and piezoelectric characteristics of the GPI type crystals is analyzed. It is shown that the most important influence on the thermodynamic characteristics of the GPI crystal is in the case of uniaxial pressure $p_{2}$, some weaker effect is in the case of $p_{3}$, and the least effect is for $p_{1}$. The influence of uniaxial pressures $p_{i}$ on the thermodynamic characteristics significantly decreases with deuteration of the GPI crystal.
PACS number(s): 77.22.-d, 77.22.Ch, 77.22.Ej, 77.65.-j, 77.80.Bh