Chapter 2Stress Effect on Thin Films 1




2.1. Introduction

Thin films of ferroelectric materials may exhibit properties drastically different from those of massive materials. This is due to the strong structure property coupling of perovskite oxides. Indeed, the deposition of a material on a different one generates 2D stresses at the interface. These stresses make it necessary to change the modeling developed for massive materials and require the development of predictive tools dedicated to the problem of ferroelectric thin films.

To guide the synthesis of thin films and the optimization of their properties, a priori knowledge of the structure is desirable. The temperature–misfit strain phase diagrams indicate what is the most stable phase depending on the temperature and the strain imposed on the material. These diagrams have been developed for monodomain and polydomain thin films. Furthermore, the domain stability maps enable us to predict whether a thin film will be polydomain or monodomain. Together, they form a theoretical framework allowing an engineering of stresses in ferroelectric thin films.

2.2. Modeling the system under consideration

The theoretical modeling of the behavior of ferroelectric thin films follows three main pathways:

1) A phenomenological, thermodynamic description of the system in the vicinity of the phase transition through a polynomial expansion of the ferroelectric order parameter (the polarization), that is to say through the Landau Ginzburg Devonshire ...

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