Defect-Related Lattice Strain and the Transition Temperature in Ferroelectric Thin Films
We propose an extension to the phenomenological thermodynamic Landau-Ginzburg-Devonshire theory to include the contribution of inhomogeneous strains caused by lattice defects to the Gibbs free energy. The model yields correction terms for dielectric and ferroelectric quantities as a function of both elastic misfit strain and defect-related strain that can be measured by x-ray diffraction techniques. We compare the correction in Curie-Weiss temperature due to elastic and inhomogeneous strain in pristine, W and Mn 1 % doped Ba0.6Sr0.4TiO3 thin films grown on the LaAlO3 substrate. If the contribution of inhomogeneous strain is included, the agreement with measurements markedly improves.