Compositional engineering of BaTiO₃/(Ba,Sr)TiO₃ ferroelectric superlattices

Epitaxial strain is one of the major factors influencing physical properties of artificial superlattice (SL) structures. One way to control the local stress in epitaxial films is altering the lattice parameters by doping. Superlattices of BT/Ba(1−x)SrxTiO3 (BT/BST) with x = (0, 0.3, 0.4, 0.5, 0.6, 0.7, 1) with a modulation period of about 80–90 Å were grown on La0.67Sr0.33MnO3 coated (100) MgO substrates by pulsed laser deposition technique. The modulated structure of the thin films was confirmed by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The increase in Sr concentration in BST layers of the SLs results in an increase in in-plane (a) and out-plane (c) compressive/tensile misfit strains in the BT/BST layers, respectively. The highest value of the dielectric constant was obtained for BT/Ba0.3Sr0.7TiO3 (BT/BST3070) and BT/Ba0.7Sr0.3TiO3 (BT/BST7030) SLs. Slim, asymmetric, but well-saturated ferroelectric hysteresis loops were observed in all SLs. Additionally, BT/BST SLs exhibited exceptionally high electric field stress sustainability over a wide range of frequency (10 kHz) and temperature (80–350 K). Temperature-dependent dielectric and ferroelectric properties show a ferroelectric relaxor behavior when the Sr content is increased in the BST layer of the SLs. Analysis of polarization versus temperature data using Landau-Devonshire theory suggests a second-order ferroelectric phase transition in these SLs. This structure can therefore be attractive in the design of a new kind of dielectric device capable in both high power and high energy density applications.