Super-tetragonal ferroelectric barium titanate through anionic overstoichiometry

Overview & Synopsis

Ferroelectric oxides, characterized by an electrical polarization that is switchable with an electric field, are an appealing class of materials for energy-efficient computing, electronics, and photonics. In thin films, the properties of ferroelectrics are commonly tuned using substrate-imposed epitaxial strain, an approach limited to biaxial strain states and a finite number of available substrates. Here, we demonstrate that is is possible to move beyond conventional epitaxial growth by using pulsed laser deposition under highly non-equilibrium conditions. Specifically, we show that this unconventional processing route allows us to stabilize a super-tetragonal phase of ferroelectric $\text{BaTiO}_3$. The key to this stabilization lies in the insertion of surplus oxygen atoms into the unit cell, resulting in peroxide bond formation that give rise to an aspect ratio of as high as 1.08. Notably, this super-tetragonal phase exhibits an enhanced ferroelectric polarization, reduced coercivity, lower leakage currents, and increased cycling endurance compared to conventional bulk-like $\text{BaTiO}_3$ films. These results, thus, showcase the potential of non-equilibrium growth for defect engineering to obtain emergent phases in complex oxides and tune their physical properties in thin films expanding the scope of traditional epitaxy.