High energy storage density achieved in Bi³⁺-Li⁺ co-doped SrTi_0.99Mn_0.01O₃ thin film via ionic pair doping-engineering

The demand for lead-free dielectric capacitors with rapid charge-discharge ability and high energy storage density is increasing owing to the rapid development of electronic equipment. Lead-free Sr_{1- x}(Bi_0.5Li_0.5)_xTi_0.99Mn_0.01O₃ (x = 0.02, 0.025, 0.03, 0.035) thin films grown on Pt/Ti/SiO₂/Si substrates were prepared by sol-gel method. A huge enhancement in polarization was found in Bi³⁺-Li⁺ co-doped SrTiO₃ thin films. The large lattice distortion and local broken-symmetry due to formation of Bi³⁺-Li⁺ ionic pairs are responsible for ferroelectricity and high polarization. The maximum polarization (42.1 μC/cm²) and largest energy storage density of 47.7 J/cm³ at 3307 kV/cm were both achieved in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film. Moreover, an excellent temperature-dependent stability was also obtained in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film from 30 to 110 °C.