The First Observation of the Tricritical Point in Ferroelectrics

Abstract

The existence of Curie critical point (tricritical point in more recent terminology) was predicted by Landau in 1935. In 1945 Ginzburg created the phenomenological theory, of ferroelectricity based on Landau theory of the second order phase transitions. Ginzburg supposed, that ferroelectric phase transition of the first order in BaTiO 3 takes place in vicinity of the critical Curie point. This correct supposition could not be confirmed experimentally at this time and accordingly the Curie critical point coordinates could not be obtained because corresponding critical pressure for BaTiO 3 is more than 20 kbar. The first experimental observation of the critical (tricritical) point and estimation of its coordinates was performed in the ferroelectric SbSI crystals in 1967 and published next year. Later on, the tricritical point was found almost in the all ferroelectrics. This paper summarizes the results of experimental investigation of tricritical point in SbSI.