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].