  We develop a phenomenological thermodynamic theory of ferroelectric BaTiO3
(BT) thin films epitaxially grown on cubic substrates using the
Landau-Devonshire eight-order potential. The constructed "misfit-temperature"
phase diagram is asymmetrical. We found that, overall view of the phase diagram
depends on the values of compliances used in calculations and provide two
qualitatively different diagrams. A thermodynamic path for BT film grown onto
particular substrate can be found using a plot of the room-temperature
tetragonal distortion (c-a)/a as a function of misfit strain.
