Phase Transitions in Ferroelectric Thin Films and Superlattices: Thermophysical Approach

Abstract

It is shown that the information about thermophysical parameters of the nanostructured ferroelectrics is a useful supplement to the traditional x-ray and dielectric data. The results of the study of the temperature dependence of heat capacity of BaTiO ₃ /MgO epitaxial thin films by dynamical 3ω method for the thickness range 50–450 nm are presented. The blurred specific heat anomalies corresponding to the phase transitions were observed, and the temperature of the transitions increases with decreasing of film thickness compared with T _c in a bulk sample. The causes of the severe smearing of specific heat anomalies as well as pronounced nonlinearity of the dependence of the transition temperature on the film thickness are discussed. Specific heat data for ferroelectric superlattices (BaTiO ₃ ) _n /(Sr TiO ₃ ) _m /Sr TiO ₃ were obtained for the first time for the films with the average thicknesses near 100 nm.

Keywords:

• Ferroelectric thin films
• ferroelectric superlattices
• ferroelectric phase transition
• specific heat
• spontaneous polarization

4. Acknowledgment

This work was supported by Russian Foundation for Basic Research, Projects 05–02-16873 and 08–02-01010-a.