Pulsed laser deposition of lead-free (Na0.5Bi0.5)1−xBaxTiO3 ferroelectric thin films with enhanced dielectric properties

Abstract

Ferroelectric lead-free (Na0.5Bi0.5)1−xBaxTiO3 thin films obtained by pulsed laser deposition have been structurally and electrically investigated for compositions, x=0 and x=0.06, in and out of the morphotropic phase boundary (MPB). Sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT), pure or in solid solution with other materials (like BaTiO3), is considered to be the best candidate material for lead-free ferroelectric and piezoelectric applications such as actuators and nonvolatile memory devices. Bulk solid solutions with BaTiO3 (BT), (1−x)NBT–xBT (NBT–x%BT) have been investigated widely, also due to a morphotropic phase boundary (MPB) with enhanced dielectric and ferroelectric properties between a rhombohedral and a tetragonal ferroelectric phase, at x=0.06. Nonetheless, to transpose bulk properties to NBT–BT thin films is a major achievement. XRD technique has been used for structural characterizations of NBT–BT films. Dielectric spectroscopy measurements were performed at room temperature in the frequency range 100Hz–1MHz. The best films show pure perovskite phase and good crystalline structure, as a function of specific deposition conditions. Unusual characteristics, especially dielectric constant values higher than those for bulk, have been found for films with specific crystallographic orientations.