Thermodynamic Relations between Anomalous Quantities near a Lambda Transition in Anisotropic Dielectrics

Abstract

The thermodynamic treatment of the λ transition in liquid helium developed by Buchingham and Fairbank is generalized for transitions in anisotropic dielectrics. Tensor relations between the heat capcity c^σ,E, the elastic compliances s_μν^T,E, the thermal expansion coefficients α_μ^σ,E, the pyroelectric coefficients p_i^σ,E and the piezoelectric coefficients d_iμ^T,E are derived, and a connection established between the symmetry and the coupling of anomalous quantities. It is shown that the asymptotic forms of the general equations lead to the Pippard—Garland equations with specified electric boundary conditions and, in addition, to a new set of equations that relate pyroelectric and piezoelectric coefficients in the transition region. Experimental data for triglycine sulfate near the ferroelectric phase transition are analyzed, and it is shown that the anomalous quantities c^σ,E, s_μν^E, α_μ^σ, and p_i^σ,E, d_iμ^E are linearly related within the temperature interval (T_c—T) T_c due to mechanical stresses.