Investigations of the nonlinearity of permittivity of a triglycine sulphate crystal above the curie temperature

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Abstract
From measurements of variations of permittivity as a function of electric field strength for various temperatures in the vicinity of Tc in the paraelectric phase, values were found for the critical exponents γ0 = γ = 0.95 ± 0.05, γ2 = 4.0 ± 0.2 and γ4 = 6.8 ± 0.5 in the temperature relations α2n = A2nτ-γ2n, where α2n are the coefficients in the expansion of the series for permittivity as a function of electric field, i.e. ε = α0 + α2E2 + α4E4 + ···. The values of gap exponents Δ4 = 1.5 ± 0.1 and Δ6 = 1.4 ± 0.2 were determined. It was also confirmed that there is good agreement as to the order of the amplitude ratios A2:A0 and A4:A2.