Strain-driven high energy storage in BaTiO₃-based lead-free epitaxial thin films

In this work, the epitaxial 0.85BaTiO₃-0.15Bi(Mg_1/2Ti_1/2)O₃ (BT-BMT) films with large compressive strain were fabricated on SrTiO₃ (001). The expansion of the unit cell volume and out-of-plane lattice parameter and the large built-in electric field (E_bi) in BT-BMT films indicate the existence of defect dipoles. It was found that the polarization and the breakdown strength can be optimized by the strain and the defects, respectively. Ultimately, a desirable energy density of 90.3 J/cm³ with efficiency of 62.3% was achieved. It suggests that strain can serve as a practical means to modulate the energy storage performance of ferroelectric epitaxial film capacitors.