Energy storage properties and enhanced breakdown strength of calcium-doped barium zirconate titanate thin films prepared by the sol–gel method

Abstract

Calcium (Ca²⁺)-doped BZT thin films, Ba_1-xCa_x Zr_0.2Ti_0.8O₃ (x = 0, 0.05, 0.1, 0.15 and 0.2), were synthesized on the Pt/Ti/SiO₂/Si substrates via sol–gel spin-coating techniques for pulse capacitor applications. The microstructures, ferroelectric properties and energy storage performance of Ba_1-xCa_xZr_0.2Ti_0.8O₃ thin films were characterized while adjusting the Ca²⁺ concentration. It is found that the Ca²⁺-doped BZT thin films exhibit single-phase perovskite structure. On increasing the Ca²⁺ concentration, the cell volume and tolerance factor declined due to the replacement of Ca²⁺ ions for the A-site ions in the BZT lattice. The average grain size and root-mean-square (RMS) roughness of Ba_1-xCa_x Zr_0.2Ti_0.8O₃ thin films with dense and uniform microstructure is refined to 44 nm and 1.55nm, respectively, with Ca²⁺ increasing up to x = 0.15. While lowering the leakage current density after Ca²⁺ modification, the breakdown field strength of Ca²⁺-doped BZT thin films is improved significantly approaching 4210 kV/cm at x = 0.15. Because of the enlarged polarization difference (P_m–P_r), the nano grain Ba_0.85Ca_0.15 Zr_0.2Ti_0.8O₃ thin film possesses an elevated energy storage density of 33.1 J/cm³ and an acceptable energy storage efficiency of 62.1% at the ultrahigh breakdown field. The Ca-doped BZT films also have remarkable cycle reliability showing a significant potential for capacitor applications.