High‐recoverable energy‐storage density and dielectric tunability in Eu3+‐doped NBT‐xSTO binary solid solution films

The Eu3+‐doped (1 − x)Na0.5Bi0.5TiO3‐xSrTiO3 (Eu‐NBT‐xSTO) thin films were prepared on Pt/Ti/SiO2/Si substrates. Raman analysis reveals that the phase structure may undergo a phase evolution of rhombohedral → rhombohedral + tetragonal (morphotropic phase boundary) → tetragonal with increasing content of STO. The scanning electron microscopy images show that the uniformity and high density of Eu‐NBT‐xSTO films were increased by adding STO, resulting in a pronounced effect on energy storage properties. The ɛ‐T curves confirm that a high phase transition diffuseness of γ = 2.02 ± 0.03 and 1.98 ± 0.03 was achieved in Eu‐NBT‐0.24STO and Eu‐NBT‐0.3STO films, respectively. Furthermore, a large recoverable energy storage density of 31.5 J cm−3 with an efficiency of 64% was obtained in Eu‐NBT‐0.3STO film, which also exhibited good thermal stability in the temperature range between −60°C and 80°C as well as long‐term stability up to 1 × 108 switching cycles. These results suggest that the Eu‐NBT‐xSTO films may be used in the novel and advanced energy storage capacitors.