Revealing the mechanism of electric-field-induced phase transition in antiferroelectric NaNbO₃ by in situ high-energy x-ray diffraction

Antiferroelectric materials exhibit electric field-induced phase transitions between antiferroelectric and ferroelectric states, which enable their use in energy storage and other applications. However, the mechanisms of these transitions are insufficiently understood. Here, we considered the electric field-induced phase transition in the lead-free antiferroelectric NaNbO$_3$. Macroscopic measurements of polarization and longitudinal, transverse, and volumetric strain were complemented with simultaneous structural investigations using high-energy x-ray radiation, yielding crystallographic strain and unit cell volume changes. The field-induced behavior can be divided into the structural antiferroelectric–ferroelectric phase transition at about 8 kV/mm and the clearly decoupled polarization switching process at about 12 kV/mm, which is associated with a large increase in polarization and strain. Decoupling of the field-induced phase transition and polarization switching is related to the randomly oriented grains and mechanical stress present at the phase boundary