The influence of crystallization route on the SrBi 2 Nb 2 O 9 thin films
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The influence of crystallization route on the SrBi2 Nb2 O9 thin films S. M. Zanetti, E. R. Leite, and E. Longo Departamento de Qu´ımica, UFSCar, P.O. Box 676, 13560-905 S˜ao Carlos, SP, Brazil
J. A. Varela Instituto de Qu´ımica, UNESP, P.O. Box 355, 14801-970 Araraquara, SP, Brazil (Received 29 January 1998; accepted 6 August 1998)
Polycrystalline SrBi2 Nb2 O9 -layered ferroelectric thin films were synthesized on PtyTiySiO2ySi substrate using the polymeric precursors solution. The dip-coated films were specular and crack-free and crystallized during firing at 700 ±C. Single-, double-, and triple-layered films were obtained by several dips in the deposition solution, and the influence of crystallization between each dip was studied. Microstructure and morphological evaluation were followed by grazing incident x-ray diffraction (GIXRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Multilayered films obtained using the intermediate-crystallized layer route present a dense microstructure with spherical grains, with a preferential orientation in the k215l direction; films obtained using the intermediate-amorphous layer route are polycrystalline and present elongated grains around 250 nm in size. I. INTRODUCTION
The bismuth-based, layer-structured perovskites include a broad family of structural forms (Am21 Bm O3m11 )21 (Bi2 O2 )22 , e.g., SrBi4 Ti4 O15 (SBIT), SrBi2 Ta2 O9 (SBT), and SrBi2 Nb2 O9 (SBN). These kinds of materials have attracted much attention due to the possibility of applications such as nonvolatile memory devices. Nonvolatile memory is an application which truly utilizes the ferroelectric nature of the films and has potentially great practical impact. Pb(Zr, Ti)O3 (PZT) has been widely studied for application to nonvolatile memory devices. However, PZT films on Pt electrodes present serious problems of degradation due to oxygen vacancies created at the interface. In addition, PZT capacitors do not maintain good electrical properties when PZT layer is ,100 nm. Recent studies have reported that these bismuth-layered materials have presented good ferroelectric properties.1,2 Several preparation methods of Bi-layer thin films such as laser ablation,1,3,4 sputtering,5 metalorganic chemical vapor deposition (MOCVD),6 – 8 sol-gel,9,10 and metalorganic decomposition,11–13 have been employed. Normally, physical methods have the disadvantage of requiring sophisticated and expensive equipment. Although the sol-gel method is considered very good in terms of stoichiometric control and introduction of dopants, it presents a serious problem of solution aging. The aging may alter the film microstructure, causing significant ferroelectric loss.14 Recently, a new approach for thin film chemical synthesis, based on the process developed by Pechini,15 has been experienced successfully for some mixed oxide compounds.16,17 The Pechini process is based on the polymeric precursors originated from a polyesterifica1026
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