Lead-free relaxor ferroelectrics are promising materials for energy storage applications. To find new material systems for electrostatic capacitors, many researches have dedicated their work to formulate new ecologically safe compositions. In our study, we have prepared (1−x)Ba(Ti0.93Sn0.07)O3−xBiYO3 (BTS7-BY) solid solutions via the solid-state method. The parent composition, Ba(Ti0.93Sn0.07)O3 is a ferroelectric-relaxor crossover material. It reduces its remanent polarization while still maintaining a high maximum polarization. Moderate substitution with BiYO3 further lowers the remanent polarization, resulting in slimmer polarization loops and increasing the energy storage efficiency to 90 %. Samples with x ≥ 0.06 show a true relaxor behavior with linear-like polarization loops with character of weakly-coupled relaxors. Breakdown strength measurements reveal a reduced breakdown strength with increasing BY content. Further investigations of the electrostriction, the band gap, and the electrical microstructure link the homogeneity and grain size of the microstructure to the resulting breakdown strength. This highlights the importance of a homogenous and small-grained microstructure for enhancing the energy storage properties. Samples with x = 0.06 exhibit the best energy storage properties with a recoverable energy density of 1.11 J/cm3 at 189 kV/cm with an energy storage efficiency of 74%.publishe
