Thin films of NaNbO3were grown on various
substrates
to investigate the effect of epitaxial strain on their structural
and electrical properties. Reciprocal space maps confirmed the presence
of epitaxial strain from +0.8% to −1.2%. A bulk-like antipolar
ground state was detected via structural characterization for NaNbO3thin films grown with strains ranging from a compressive
strain of 0.8% to small tensile strains, up to −0.2%. For larger
tensile strains on the other hand, no indication of antipolar displacements
can be detected, even beyond the relaxation of the film at larger
thicknesses. Electrical characterization revealed a ferroelectric
hysteresis loop for thin films under a strain of +0.8% to −0.2%,
while the films under larger tensile strain showed no out-of-plane
polarization component. However, the films with a compressive strain
of 0.8% present a saturation polarization of up to 55 μC·cm–2, more than twice as large for films grown under conditions
with small strain, which is also larger than the highest values reported
for bulk materials. Our results indicate the high potential for strain
engineering in antiferroelectric materials, as the antipolar ground
state could be retained with compressive strain. The observed enhancement
of the saturation polarization by strain allows for substantial increase
of energy density of the capacitors with antiferroelectric materials.