Improvement of energy storage density with trace amounts of ZrO2 additives fabricated by wet-chemical method

Lead-free (1-x)[0.6SrTiO3-0.4Na0.5Bi0.5TiO3]-xZrO2 ceramics (STNBT-xZr) were synthesized in single perovskite phase. The average grain size decreased from 3.2 μm (x = 0.1 mol%) to 1.6 μm (x = 0.6 mol%) related to the addition of ZrO2 powders prepared by microwave hydrothermal method. With the increasing of ZrO2 content, the permittivity decreased gradually, and the breakdown strength (Eb) was remarkably improved due to composition induced disturbing of long range ferroelectric order. The increase of Eb led to the improvement of the recoverable energy storage density (Wre) from 1.80 J/cm3 (x = 0.1 mol%) to 2.84 J/cm3 (x = 0.5 mol%). However, when Zr4+ content was more than 0.5 mol%, the Wre decreased from 2.84 J/cm3 to 2.26 J/cm3 (x = 0.6 mol%) due to the reduction of the maximum polarization. The best energy storage properties were achieved in STNBT-xZr ceramic with Zr4+ content of x = 0.5 mol%, which exhibited the Wre of 2.77-2.84 J/cm3 in the range of 4-40 Hz, revealing an excellent frequency stability. All these results demonstrate the STNBT-xZr (x = 0.5 mol%) ceramics are quite promising for frequency-stable energy storage applications.