Thermally Stable Capacitive\nEnergy-Density and Colossal\nElectrocaloric and Pyroelectric Effects of Sm-Doped Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>–PbTiO<sub>3</sub> Thin Films

Sm-doped Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>–PbTiO<sub>3</sub> (Sm-PMN–PT) bulk materials have\nrevealed outstanding\nferroelectric and piezoelectric properties due to enhanced local structural\nheterogeneity. In this study, we further explore the potential of\nSm-PMN–PT by fabricating epitaxial thin films by pulsed laser\ndeposition, revealing that Sm doping significantly improves the capacitive\nenergy-storage, piezoelectric, electrocaloric, and pyroelectric properties\nof PMN–PT thin films. These Sm-PMN–PT thin films exhibit\nfatigue-free performance up to 10<sup>9</sup> charge–discharge\ncycles and maintain thermal stability across a wide temperature range\nfrom −40 to 200 °C. Notably, the films demonstrate a colossal\nelectrocaloric effect with a temperature change of 59.4 K and a remarkable\npyroelectric energy density reaching 40 J cm<sup>–3</sup>.\nBy using scanning transmission electron microscopy and phase-field\nmodeling, we revealed that these exceptional properties arise from\nthe increased local structural heterogeneity and strong local electric\nfields along spontaneous polarization directions, facilitating the\nnucleation of polymorphic nanodomains characterized by a slush-like\npolar structure. These findings highlight the enormous potential of\nSm-PMN–PT films in capacitive energy storage and solid-state\nelectrothermal energy interconversion. Furthermore, this approach\nholds broad potential for other relaxor ferroelectrics by enabling\nthe manipulation of nanodomain structures, paving the way for developing\nrobust multifunctional materials.