Thermodynamics of Epitaxial Ferroelectric Films.

The problem of phase transitions and physical properties of the BaTiO{sub 3}-type films on the (001) single-crystal substrates of the cubic syngony was solved in the limits of the Landau-Devonshire thermodynamics. The thermoelastic film-substrate interaction caused by the difference between thermal expansion coefficients was strictly taken into consideration. The model was based on the following assumptions: (1) the film is closely conjugated with the substrate; (2) the film is sufficiently thick to find itself unstrained at the growth temperature T{sub s} (growth stresses were compensated by misfit dislocations), and (3) the film is sufficiently thin, and the stresses arising at the temperatures T > T{sub s} may be considered to be uniform.