Unlocking high capacitive energy-density in Sm-doped Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films via strain and domain engineering

Relaxor ferroelectrics have garnered significant attention in the field of energy storage due to their exceptional properties, such as high recoverable energy density and impressive efficiency. In this work, we explore (001)-oriented and partially strained Sm-doped Pb(Mg1/3Nb2/3)O3-30PbTiO3 (Sm-PMN-30PT) thin films, prepared by pulsed laser deposition using TbScO3 substrates and SrRuO3 electrodes. We employ a comprehensive approach to evaluate the structural, compositional, and energy storage properties of Sm-PMN-30PT thin films. Our study demonstrates an ultra-high energy density of 116 J cm-3 and an efficiency of 73%, along with excellent thermal stability and fatigue-free energy storage properties in Sm-PMN-30PT thin films. Strain analysis of the heterostructures, performed using reciprocal space mapping (RSM) and geometric phase analysis (GPA), reveal a gradual strain relaxation across the film thickness. This results in imprinted polarization-electric field loops. Additionally, high-angle annular dark field imaging with scanning transmission electron microscopy (HAADF-STEM) depicted the existence of a strongly disordered slush-like domain structure, consisting of interconnected rhombohedral and tetragonal polymorphic nanodomains around 2-5 nm in size, and inclined "head-to-tail" polarization between neighboring domains. These results highlight the great potential of Sm-PMN-30PT films for high-capacitive energy storage devices.