Thickness dependence and strain effects in NaNbO₃ thin films

NaNbO₃ is one of the most complex perovskite oxides, with room-temperature antiferroelectricity and several temperature-dependent phase transitions in bulk^1,2. Despite extensive studies in bulk^3,4, relatively little is known about the evolution of structure and properties in NaNbO₃ thin films. Here, we explore the effects of thickness and misfit strain on the structure and electrical properties of NaNbO₃ thin-film heterostructures. Using pulsed laser deposition, we synthesize epitaxially-strained NaNbO₃ thin films on SrTiO₃ (001) and DyScO₃ (110) substrates. Using X-ray diffraction and scanning transmission electron microscopy, we characterize the crystal structures and compute polarization via atomic displacements. We observe strain-induced ferroelectricity and characterize this via electrical measurements and piezoresponse force microscopy to measure the polarization-electric field hysteresis loops and ferroelectric domain structures. This work provides new insights into the structure and electrical property evolution of these lead-free ferroelectric thin films.

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2. H.D. Megaw Ferroelectrics 7, 87–89 (1974).

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4. Y. I. Yuzyuk et al. J. Phys.: Condens. Matter 17, 4977 (2005).