Hydrothermal Epitaxy of I:V Perovskite Thin Films
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Hydrothermal Epitaxy of I:V Perovskite Thin Films
Gregory K. L. Goh* and Suresh K. Donthu Institute of Materials Research and Engineering 3 Research Link, Singapore 117602, Singapore *Corresponding author: [email protected] ABSTRACT Although epitaxial II:IV perovskite films like BaTiO3 and Pb(Zr,Ti)O3 have been grown by the hydrothermal method, there are hardly any reports on the growth of I:V perovskite thin films by this low temperature technique. In this study, thin films of NaNbO3, KTaO3 and KNbO3 were grown on (100) oriented single crystal SrTiO3 substrates by the hydrothermal method at 200oC and below. X-ray diffraction (XRD) revealed that the as-synthesized films were epitaxial with one of their original cubic axes normal to the substrate (100) plane. Scanning electron microscopy (SEM) showed that the films formed by an island growth mechanism. KTaO3 was also used as a buffer layer in the growth of KNbO3 films in order to investigate the effect of lattice mismatch on surface morphology and epitaxial quality, as determined by SEM and XRD rocking curve measurements, respectively.
INTRODUCTION KNbO3 is a very promising material for electro-optic, non-linear optical and photorefractive applications such as frequency doubling, wave guiding and holographic storage [1-3]. KTaO3 exhibits a dielectric nonlinearity at low temperatures near the transition temperature of high Tc superconductors and can be used as a tunable element in microwave circuits. As such, it has been used as a substrate for the growth of high Tc superconductors such as YBa2Cu3O7-δ [4-6]. Its close lattice match with KNbO3 also makes KTaO3 an ideal substrate or buffer layer for the growth of KNbO3 films [7]. As NaNbO3 is anti-ferroelectric at room temperature, it has attracted comparatively less attention than the potassium compounds. Recently though, it has been shown that when combined with KNbO3 in solid solution, (Na,K)NbO3 is a promising candidate for applications in non-volatile memory, surface acoustic wave devices, micro-sensors and actuators [8,9]. Hydrothermal epitaxy is a technique that utilizes aqueous chemical reactions that occur at low temperatures to form heteroepitaxial thin films. As only temperatures around 200oC and lower are used in this method of film growth, problems associated with high processing temperatures that are detrimental to device properties such as residual thermal stresses, interdiffusion and reactions at the film/substrate interface, can be avoided. This, and the fact that ultrahigh vacuum equipment is not used, result in lower capital and operating costs. In addition, the use of less temperature resistant substrates like polymers becomes possible. To date, only epitaxial II:IV perovskite films like BaTiO3, SrTiO3 and Pb(Zr,Ti)O3 have been grown hydrothermally [10,11]. This paper reports the growth of epitaxial films of I:V perovskites like NaNbO3, KTaO3 and KNbO3 on (100) single crystal SrTiO3 substrates by the hydrothermal method. D10.13.1 Downloaded from https://www.cambridge.org/core. Access paid by the UC
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