Ferroelectric phase transitions in tensile-strained NaNbO3 epitaxial films probed by in situ x-ray diffraction
2Department of Nanostructures & Layers, Leibniz Institut für Kristallzüchtung, Berlin, Germany
3Department of Microstructure, Paul-Drude-Institut für Festkörperelektronik (PDI), Berlin, Germany
4Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, School of Electronic Science and Engineering & The International Joint Laboratory for Micro/Nano Manufacturing and M, Xi’an Jiaotong University, Xi'an, China
Polymorphic phase boundaries are of fundamental and technological interest because of the anomalies and improvement of piezo- and ferroelectric properties observed in these regions.[1] Specifically, NaNbO3 is a perovskite that has been extensively studied as bulk material due to its complex series of thermal phase transitions.[2] The changes in its crystal structure lead to different anti-, ferro- and paraelectric phases, which can be particularly relevant for microelectronics. For such applications it is advantageous for materials to be incorporated as thin films.
In this context, strain engineering is a valuable tool, for allowing tuning of the piezo-/ferroelectric properties of the film. However, in contrast to bulk NaNbO3, not much is known about the phase transitions of NaNbO3 epitaxial thin films.
In the present work we have studied tensile-strained NaNbO3 thin films epitaxially grown on (110) DyScO3 orthorhombic substrates.[3] In situ synchrotron x-ray diffraction was used to identify a ferroelectric-to-ferroelectric phase transition in the temperature range between 230 and 350 °C, along with a wide-range thermal hysteresis. While at room temperature an in-plane a1a2 monoclinic phase was observed, a slightly distorted a1/a2 orthorhombic phase was found at high temperatures. The phase symmetry and the associated domain morphology at high temperatures showed great similarities to those observed in K0.9Na0.1NbO3 thin films on (110) NdScO3.[4]
[1] H. D. Chen, K. R. Udayakumar, C. J. Gaskey, and L. E. Cross, Appl. Phys. Lett. 67, 3411-3413 (1995).
[2] G. Shirane, R. Newnham, and R. Pepinsky, Phys. Rev. 96, 581–588 (1954).
[3] M. de Oliveira Guimarães, C. Richter, M. Hanke, S. Bin Anooz, Y. Wang, J. Schwazkopf, M. Schmidbauer, J. Appl. Phys. 132, accepted for publication (doi: 10.1063/5.0113949).
[4] M. Schmidbauer, L. Bogula, B. Wang, M. Hanke, L. von Helden, A. Ladera, J.-J. Wang, L.-Q. Chen, and J. Schwarzkopf, J. Appl. Phys. 128, 184101 (2020)
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