Multilayered Structures of SrNb 0.1 Ti 0.9 O 3 /La 0.8 Sr 0.2 MnO 3 /SrTiO 3 Prepared by Laser Molecular Beam Epitaxy
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H.B. Lu, F. Chen, Z.H. Chen, and G.Z. Yang Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, 100080 Beijing, China (Received 11 September 2001; accepted 26 December 2001)
Multilayer oxides of SrNb0.1Ti0.9O3 /La0.8Sr0.2MnO3/SrTiO3 have been grown by computer-controlled laser molecular beam epitaxy and characterized by transmission electron microscopy. Electron microdiffractions and high-resolution imaging reveal that the as-prepared thin film of La0.8Sr0.2MnO3 with thickness of 200 nm is epitaxially grown on the SrTiO3(001) substrate and the SrNb0.1Ti0.9O3 with thickness of 250 nm epitaxially on the as-received La0.8Sr0.2MnO3 film. The microstructures in the La0.8Sr0.2MnO3 film are clarified in terms of the oriented microdomains. In contrast, microstructures in SNTO are featured by the formation of superstructures due to charge ordering. Crystallographic relationships of these domains are discussed on the basis of an orthorhombic cell and rationalized by theoretical calculations based on a geometrical model.
I. INTRODUCTION
Perovskite-based oxides have received much attention because of their promising electric, optical, and magnetic properties. In addition, recent studies have shown that multilayered oxides, combined at an atomic scale, provide quite different properties compared with single film of each of these oxides. For example, when ferroelectric BaTiO3 (BTO) and paraelectric SrTiO3 (STO) are stacked alternately, the dielectric constants H were greatly enhanced and the high H values were kept in a broad range of both thickness and temperature because of the in-plane stress resulting from the lattice mismatch between BTO and STO.1,2 Second-harmonic generation coefficients were also greatly enhanced by the BTO/STO superlattice structure with the maximum value of d33 ⳱ 156.5 pm /V, being more than 1 order of magnitude larger than that of bulk BTO crystal.3 It is believed that multilayer films and the artificial superlattice of the functional oxides have potential applications in the fields of physics and materials science. On the other hand, members of the La1−xAxMnO3 (A ⳱ Ca, Sr, Ba) compound family, which have a perovskite-based structure, have been the focus of much attention since the discovery of the colossal magnetoresistance (CMR) in these oxides. 4–7 And a)
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J. Mater. Res., Vol. 17, No. 3, Mar 2002 Downloaded: 16 Mar 2015
in the past few years, thin films of La1−xAxMnO3 (A ⳱ Ca, Sr, Ba) have been grown on several substrates by variant techniques such as pulsed laser deposition,5 metalorganic chemical vapor deposition,8 and dc magnetron sputtering.9 Both CMR La0.8Sr0.2MnO3 and paraelectric SrTiO3 are of technological interest. It was proposed that a thinfilm combination of these two oxides might provide much more promising properties. To the best of our knowledge, little work has been done on the layer combination of CMR material and paraelectric oxide. In this work, m
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