Structural and electrical properties of strontium barium niobate thin films crystallized by conventional furnace and rap
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Arau´joa) Universidade Estadual Paulista, Departamento de Fı´sica e Quı´mica, Grupo de Vidros e Ceraˆmicas, Caixa Postal 31, 15385-000 Ilha Solteira, SP, Brazil
J.A. Eiras Universidade Federal de Sa˜o Carlos, Departamento de Fı´sica, Grupo de Ceraˆmicas Ferroele´tricas, Caixa Postal 676, 13565-670 Sa˜o Carlos, SP, Brazil (Received 5 September 2000; accepted August 6, 2001)
Strontium barium niobate (SBN) thin films were crystallized by conventional electric furnace annealing and by rapid-thermal annealing (RTA) at different temperatures. The average grain size of films was 70 nm and thickness around 500 nm. Using x-ray diffraction, we identified the presence of polycrystalline SBN phase for films annealed from 500 to 700 °C in both cases. Phases such as SrNb2O6 and BaNb2O6 were predominantly crystallized in films annealed at 500 °C, disappearing at higher temperatures. Dielectric and ferroelectric parameters obtained from films crystallized by conventional furnace and RTA presented essentially the same values.
I. INTRODUCTION
The tungsten bronze family is one of several ferroelectric materials. Since 1949, when the tungsten bronze structure was deduced by Magneli,1 numerous tungsten bronzes have been synthesized. The tungsten bronze family includes niobates such as (Sr,Ba)Nb2O6 (SBN), (Pb,Ba)Nb2O6 (PBN), and (Pb,K)Nb2O6 (PKN). PBN and PKN are orthorhombic tungsten bronze structure with a point group mm2. On the other hand, SBN (Srx Ba1−x Nb2O6), with 0.25 < x < 0.75, presents a tetragonal (4mm) phase at room temperature. A solid solution of SBN exists in the binary SrNb2O6–BaNb2O6 system. Investigations using x-ray diffraction (XRD) suggested a morphotropic phase boundary around x ⳱ 0.25, which is characterized by the coexistence of the tetragonal and orthorhombic phases.2 The excellent ferroelectric and electro-optic properties exhibited by SBN make this material promising for a variety of applications. SBN has received great attention as a ferroelectric material due to its large pyroelectric coefficient,3 piezoelectric,4 and electro-optic properties.5
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 10, Oct 2001
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In recent years, the development of integrated optical devices has stimulated the demand for thin films using attractive materials such as SBN. SBN thin films have been prepared by several techniques like sol-gel processing,6 pulsed laser deposition,7 and metalorganic chemical vapor deposition (MOCVD).8 Large-scale processing of high-quality thin films requires lowtemperature synthesis, high reproducibility, simplicity in all processing steps, and low cost. Due to this fact, the search for new routes for film preparation remains an interesting and open subject in order to improve the stability of complex solutions, the control of the stoichiometry of the film composition, or to reduce the cost of the process. Very recently, the preparation of SBN thin films by a chemical method based on a
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