Enhancement of Energy Storage Performance by Criticality in Lead-Free Relaxor Ferroelectrics

In modern electronic systems and energy conversion, efficient capacitors with large energy densities are needed. Relaxor ferroelectrics show the potential to achieve those requirements. The lead-free relaxor ferroelectric 0.852(Na1/2Bi1/2TiO3)-0.028(BaTiO3)-0.12(K1/2Bi1/2TiO3) is investigated exhibiting the behavior of a wide range of Na1/2Bi1/2TiO3-based relaxor systems. The criticality of this system is analyzed and a full electric field-temperature phase diagram is constructed. The energy storage performance is determined from polarization measurements in a wide temperature range. It is found that energy density and especially the efficiency is largely increased in the vicinity of the critical end point of the relaxor system. The concept of criticality is widely applicable to lead-based and lead-free relaxor ferroelectrics and therefore an important approach to increase energy storage performance in those systems.