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 cσ,E, the elastic compliances sμνT,E, the thermal expansion coefficients αμσ,E, the pyroelectric coefficients piσ,E and the piezoelectric coefficients diμT,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 cσ,E, sμνE, αμσ, and piσ,E, diμE are linearly related within the temperature interval (Tc—T) <16°, where the constants of proportionality give the numerical values of the components of a tensor describing the change of Tc due to mechanical stresses.