Abstract
A Landau-Ginsburg-Devonshire-type theory is used to describe the mechanical substrate effect on equilibrium states and phase transitions in epitaxial thin films. The misfit strain-temperature phase diagram of films is developed taking into account the existence of two coupled instabilities (antiferrodistortive and ferroelectric) in this crystal. It is shown that films remain paraelectric down to 0 K only in a narrow range of small negative misfit strains between and Outside this “paraelectric gap,” the 2D clamping and straining of the film by the substrate leads to the appearance of ferroelectricity in films. The temperature of the ferroelectric transition increases rapidly outside the aforementioned misfit strain range.
- Received 2 July 1999
DOI:https://doi.org/10.1103/PhysRevB.61.R825
©2000 American Physical Society