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October, 2021

High performance energy storage devices are in great high demand for electric vehicles (EVs) and other high temperature capacitor applications, where it is critical to store and deliver energy quickly. Ferroelectric materials have high capacitance and can deliver energy more quickly than conventional batteries.

This work originated from a visiting student from Tsinghua, Hao Pan. who came for 1 year to work in the Driscoll group. He was continuing our work in the group, first started by a part III student, who had been engineering Sm2O3 nanopillars into ferroelectric films (high Sm content added to alloy films of BaTiO3+BiFeO3) to learn about their influence on energy storage capability using new straining effects.  Hao first needed to learn about the influence of Sm doping of the film (i.e. at lower Sm doping levels) before studying the influence of higher Sm contents which give both nanopillar formation and Sm doping of the film. The nanopillar paper will follow this one. 

Hao found the low Sm doping produced nanoscale polar clusters in the films. These clusters (smaller than nanodomains) meant that polarization switching hysteresis was nearly eliminated. Hence, there was greatly weakened domain intercoupling and hence a strongly reduced domain switching energy barrier. This led to the ultimate relaxor ferroelectric.  Thus ultrahigh energy was stored in the films because very little energy was lost upon cycling through the ferroelectric hysteresis loop.  An energy density of 152 J/cc with high efficiency (>90% at an electric field of 3.5 MV/cm) was achieved. At the same time, a high polarization was achieved.

Figure: Energy density and efficiency of Sm-doped BaTiO3-BiFeO3 thin films for molar doping fractions of Sm from 0 to 0.45.

Hao Pan et al., "Ultrahigh energy storage in superparaelectric relaxor ferroelectrics", Science 374 100–104 (2021) 1 October 2021

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