BEHAVIOUR OF SPECIFIC HEAT Cp THERMAL EXPANSION β AND ISOTHERMAL COMPRESSIBILITY kT NEAR FERROELECTRIC TRANSITIONS

Abstract

The ordinary concepts of the order of phase changes are not suitable near dielectric transitions which show logarithmic or other infinities in specific heats. The application of the more general Pippard scheme under such circumstances I studied. The linear correlations among the heat capacity, thermal expansion, elastic compressibility and pressure derivative of Tc are discussed in the case of triglycine sulphate, sodium nitrite, potassium-dihydrogen phosphate, barium titanate and lead titante. In the case of the first two, a discussion of the behavior of individual coefficients of linear expansion and compliance moduli is also possible. It is suggested that irrespective of the order of the transitions, the Pippard relations should be used whenever the thermodynamic qualities show very large variations as Tn is approached.