Evolution of low symmetric phase in strained epitaxial (Ba_0.5, Sr_0.5)TiO₃ thin films grown on Si

The evolution of low symmetric phases was investigated in epitaxial (Ba_0.5,Sr_0.5)TiO₃ (BST) thin films grown on Si with yttria stabilized zirconia (YSZ). Paraelectric cubic BST thin films, when exposed to tensile strain primarily due to Si, present low symmetric phases, tetragonal c and monoclinic r phases, depending on the thickness of the BST thin films. When BST films are thin (<80 nm), BST thin layers are in a mixed state of r and c phases. As the thickness of the BST layers further increases, the c phase rapidly disappears, and the monoclinic r phase becomes predominant. These strained BST thin films exhibit non-zero polarization and manifest themselves by non-volatility in a metal-ferroelectric-insulator structure on Si, which is attributed to the non-cubic phases developed by strained BST thin films.