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In this work, Mn modified 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 thin films (abbreviation for BNT-BT-Mnx) are prepared on Pt/Ti/SiO2/Si substrate via sol-gel and spin-coating. The influences of Mn dopant on the microstructural characteristics, dielectric and energy storage performances are studied systematically. It is found that by incorporating the Mn into BNT-BT, the breakdown strength and maximum polarization are enhanced dramatically, leading to the giant energy storage density of 54 J/cm3, with high permittivity 355 at 1 kHz. Moreover, the dominant leakage conduction mechanisms of the thin films are studied by linear fitting method, revealing that the leakage current mechanism of BNT-BT-Mnx films transforms from space-charge-limited conduction (SCLC) to Schottky emission as the increasing of electric field. The excellent energy storage density as well as dielectric properties suggest that BNT-BT-Mn6 thin film might be an attractive lead-free material for energy storage devices.

Due to advances in electronic device integration, miniaturization, and performance requirements, dielectric materials with a high energy storage density are required. Here, new BiMg0.5Ti0.5O3 lead-free energy storage thin films with excess Mg (i.e., nominal BiMgyTi0.5O3, with y = 0.50-0.62) were deposited on Pt/Ti/SiO2/Si substrates by sol-gel and spin-coating methods. The introduction of excess Mg can obviously increase the dielectric breakdown strength of thin films due to the appearance of an amorphous phase. The maximum recoverable energy storage density increased from 26 J/cm3 at y = 0.50 to 44.1 J/cm3 at y = 0.56. Furthermore, the dielectric films exhibited excellent thermal stability of the energy storage density from 30 °C to 100 °C, indicating that bismuth-magnesium-titanium films are promising candidates for next-generation lead-free energy storage capacitor applications.

Pure perovskite Bi(Mg0.5Tix)O3 (abbreviated as BMTx) thin films are successfully fabricated on Pt/Ti/SiO2/Si substrates by a sol–gel method, where the excess TiO2 with an amorphous structure is designed to improve the energy storage performance. The dielectric breakdown strength is found to be abruptly improved for the sample with x ≥ 0.65 due to the synergistic contributions from the fine grain size and amorphous phase structure, which greatly decreases the leakage current. Of particular significance is that BMTx with x = 0.75 exhibits a super high recoverable energy storage density of 126 J cm−3 at 5000 kV cm−1, demonstrating the great potential of environmentally friendly BMTx thin films for energy storage capacitor applications.

In this study, energy-storage and dielectric performances of x mol% (x = 0, 2, 4, 6) Fe-doped 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (abbreviated as 0.94BNT-0.06BT-Fex) ferroelectric thin films were prepared through sol-gel process. Fe-doped BNT-BT thin films were found to have slimmer hysteresis with higher maximum polarization (Ps), lower remanent polarization (Pr), higher breakdown strength and much larger dielectric constant. Optimal energy-storage properties were obtained for 0.96BNT-0.04BT-Fe2 thin films, with a breakdown strength, energy-storage density and efficiency of 2500 kV/cm, 33 J/cm3, 67.8%, respectively. Simultaneously, the leakage mechanisms of the 0.96BNT-0.04BT-Fex were investigated, and influences of the oxygen vacancies on the leakage current as well as breakdown strength were discussed. The outstanding properties of our thin film indicate its usage in advanced high-energy-storage capacitors.

Lead-free (0.94-x)Bi0.5Na0.5TiO3–0.06BaTiO3−xSrTiO3 (abbreviated as BNT-BT-xST, x = 0, 0.05, 0.10, 0.15, 0.20) thin films were grown onto the Pt/Ti/SiO2/Si substrate via a sol-gel/spin-coating method. Effect of Sr introduction on the microstructures, dielectric properties and energy-storage density of the thin films was researched. As a consequence, the addition of ST enhanced the maximum polarization and dielectric constant of the thin films. BNT-BT-0.05ST thin film existed high maximum recoverable energy-storage densigty (Ue) 22.5 J/cm3, dielectric constant 1120 and low dielectric loss about 0.04 at 1 kHz. Moreover, the thin films showed excellent dielectric temperature stability at the measured temperature range among 25–200 °C. These results indicated that BNT-BT-0.05ST thin film can be a promising candidate for lead-free energy storage capacitor.