Dielectric properties in heteroepitaxial Ba0.6Sr0.4TiO3 thin films: Effectof internal stresses and dislocation-type defects

A series of heteroepitaxial Ba0.6Sr0.4TiO3 were grown on 0.29(LaAlO3):0.35( Sr2TaAlO6) substrates using pulsed-laser deposition. X-ray characterization revealed compressive in-plane stresses in the thinnest films, which were r elaxed in a continuous fashion with increasing thickness. A theoretical tre atment of the misfit strain was in good agreement with the measured out-of- plane lattice parameter. The low-frequency dielectric constant was measured to be significantly less than the bulk value and found to decrease rapidly for films less than 100 nm. A thermodynamic model was developed to underst and the reduction in dielectric constant. By observing the microstructure u sing plan-view and cross-section transmission electron microscopy, we ident ified local strain associated with a threading dislocation density on the o rder of 10(11) cm(-2) as a possible mechanism for dielectric degradation in these films. (C) 2000 American Institute of Physics. [S0003-6951(00)00937- 2].