Phase transitions in epitaxial $Ba0.5Sr0.5TiO3$ thin films Available to Purchase

$Ba0.5Sr0.5TiO3$ (BST) thin-film capacitor structures with various thicknesses, $(50–1200nm)$ and different strain conditions (on lanthanum strontium cobalt oxide $La0.5Sr0.5CoO3$ and strontium ruthenate $SrRuO3$ buffer layers) were made using pulsed laser deposition, and characterized by x-ray diffraction. The out-of-plane lattice parameter was followed as a function of temperature within the $100–300K$ temperature interval. The phase sequence (cubic-tetragonal-orthorhombic-rhombohedral) known to exist in the bulk analog is shown to be strongly affected by both the stress conditions imposed by the buffer layer and the thickness of the BST film itself. Thus, no phase transition was found for the in-plane compressed BST films. On the stress-free BST films, on the contrary, more phase transitions were observed. It appeared that the complexity of structural phase transitions increased as the film thickness in this system was reduced.