Bismuth layer-structured Bi4Ti3O12-CaBi4Ti4O15 intergrowth ferroelectric films for high-performance dielectric energy storage on Si substrate

Bismuth layer-structured ferroelectrics (BLSFs) have shown a great design capability for electrical energy storage, due to a highly anisotropic lattice and dielectric property. In this work, we add another notch to their qualifications as high energy density dielectrics, by demonstrating an ultrahigh recyclable energy density (Wrec 151.1 J/cm3 @ 4 MV/cm) and a good energy efficiency (q 72.0%) in Bi4Ti3O12-CaBi4Ti4O15 intergrowth ferroelectric films integrated on Si. This performance was achieved by the combination of a high spontaneous polarization (Ps) of the intergrown superlattice, and a polycrystalline nanograin microstructure. The high Ps is obtained through design of a special lattice, which determines the up limit of the energy density. On the other hand, the nanograin structure corresponds to a reduce remnant polarization, an intermediate dielectric constant and a delayed polarization saturation, all are ideal features for achieving a high recyclable energy density and energy efficiency. Such a structure is the consequence of a limited grain growth under the effect of a buffer layer. Lastly, a remarkable fatigue-resistance and an excellent charge-retaining ability were exhibited by these lead-free BLSF films. We expect this work will pave the way for designing high performance bismuth layer-structured ferroelectric films targeted for dielectric energy storage applications.