Lead-free relaxor ferroelectrics BaTiO₃-BiYO₃ as energy storage materials

The growing population and the increasing energy demand require new energy storage systems. The current energy crisis makes this more obvious than ever. Dielectric capacitors have regained interest particularly in the field of pulse power applications due to their high power density and fast charge-discharge rate. Limiting factors in linear dielectric capacitors are the low energy storage density and low energy efficiency. Relaxor ferroelectrics are promising candidates to overcome these challenges due to their slim polarization hysteresis which increases the energy storage density and the energy efficiency while maintaining high power density. BaTiO₃-BiMeO₃ (where Me = Mg, Nb, Al, Ta, Zn) compositions are promising candidates as lead-free relaxor materials for capacitors.

In this work, we combine Ba(Ti_0.93Sn_0.07)O₃ with BiYO₃ to induce relaxor behavior in the ferroelectric base material. The heterovalent substitution in both the A- and B-sites of the perovskite structure should promote the relaxor state at a relatively low content of BiYO₃. XRD measurements reveal a crossover from a tetragonal to a pseudocubic phase with increasing BiYO₃ concentration. Simultaneously, the impedance spectroscopy shows that the phase transition becomes highly diffuse and exhibits strong frequency dispersion which is typical for relaxor ferroelectrics. For the composition with x = 0.08, the polarization has a linear-like response with a high energy storage efficiency of 89 % and a recoverable energy density of 0.99 J/cm³ at 180 kV/cm.