High recoverable energy storage density in (1-x)Bi0.5(Na0.8K0.2)0.5TiO3-xSrZrO3 thin films prepared by a sol-gel method

Lead-free (1-x)Bi0.5(Na0.8K0.2)0.5TiO3-xSrZrO3 (abbreviated as BNKT-100xSZ) thin films were deposited on Pt(111)/Ti/SiO2/Si using sol-gel/spin coating method. With the addition of SZ, the long-range ferroelectric order dominant in BNKT is disrupted, which boosts the ferroelectric relaxor behavior. Consequently, a high recoverable energy density of 34.69 J/cm3 combined with an efficiency of 59.32% was achieved at the optimal composition of BNKT-15SZ under a high electric field of 2100 kV/cm, which can be ascribed to the slim P-E loops induced by strong relaxor behavior (γ = 1.93) and the enhanced breakdown strength. Moreover, BNKT-15SZ thin film capacitor presents a good thermal stability with minimal variations of the energy density (<10%) and the energy storage efficiency (<5%) over a wide temperature range of 30-100 °C. The results indicated that the BNKT-100xSZ thin films may be a promising environmental-friendly material for energy storage applications.