Title: Nonlinear background corrections to dielectric permittivity of ferroics and multiferroics
Author(s):

	I. S. Girnyk (Physics Department, Ivan Franko National University of Lviv, 50 Drahomanov Street, 79005 Lviv, Ukraine),
	B. I. Horon (Physics Department, Ivan Franko National University of Lviv, 50 Drahomanov Street, 79005 Lviv, Ukraine; Electronics and Computer Technologies Department, Ivan Franko National University of Lviv, 107 Tarnavskyi Street, 79017 Lviv, Ukraine),
	V. B. Kapustianyk (Physics Department, Ivan Franko National University of Lviv, 50 Drahomanov Street, 79005 Lviv, Ukraine),
	O. S. Kushnir (Electronics and Computer Technologies Department, Ivan Franko National University of Lviv, 107 Tarnavskyi Street, 79017 Lviv, Ukraine),
	R. Y. Shopa (Department of Complex Systems, National Centre for Nuclear Research, 05-400 Otwock-Świerk, Poland)

Temperature measurements of dielectric permittivity are performed for nonstoichiometric ferroelectric lead germanate Pb_4.95Ge₃O₁₁ and multiferroic solid solution [N(C₂H₅)₄]₂CoClBr₃. Unlike the heat capacity data, the analysis of the dielectric permittivity of ferroics is usually performed at the assumption that the dielectric `background' is negligible compared with its critical part. In this work we quantitatively interpret the dielectric properties of the single crystals mentioned above and the appropriate literature data for multiferroic Sr₂IrO₄ crystals, using generalized Curie-Weiss formulas that combine corrections due to a nonlinear temperature-dependent dielectric background, a modified critical index of electric susceptibility, and a diffuse character of phase transition. We argue that taking account of the temperature dependent dielectric background can improve notably the quantitative analysis of PTs for a number of classes of the ferroic materials.

Key words: ferroelectrics, phase transitions, diffuse phase transitions, dielectric permittivity, critical behavior, lead germanate

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