Nonisothermal reaction kinetics and preparation of ferroelectric strontium bismuth niobate with a layered perovskite str
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Ferroelectric layered perovskite SrBi2Nb2O9 has been successfully prepared through a new process using BiNbO4 as a precursor. The SrBi2Nb2O9 formation mechanism was investigated using a nonisothermal analysis method at constant heating rates. The weight loss recorded in thermal analysis under different heating rates was analogized to the reaction conversion. A combination of the differential and integral methods was introduced to solve the reaction mechanisms. Analysis using the differential method revealed that two kinds of diffusion-controlled models have higher linear correlation coefficients than other models. Based on the integral method principle, a new integral equation combining the Arrhenius equation and the Lobatto approximation was derived in this study. The established equation significantly simplified the conventional calculation process and improved the accuracy for predicting the reaction models. Analysis using the integral method corroborated that the SrBi2Nb2O9 formation mechanism is governed by Jander’s diffusion controlled model, and the activation energy was calculated to be 192.1 kJ/mol. The proposed methods and the derived equations can be further applied to other solid-state-reaction systems to elucidate their reaction kinetics and estimate the related kinetic parameters.
I. INTRODUCTION
Ferroelectric materials have attracted considerable worldwide interest for their applications to nonvolatile ferroelectric random-access memory (FeRAM).1,2 To improve the electric properties of ferroelectric materials, various kinds of materials have been intensively investigated. SrBi2Nb2O9 and SrBiTa2O9-related compounds have received increasing attention. Various research groups demonstrate that SrBiM2O9 (M ⳱ Nb, Ta) related materials exhibit fatigue-free characteristics, low leakage current, long data retention time, and stable imprint characteristics.3–8 SrBi2Nb2O9 material is a layered-type perovskite ferroelectric, as illustrated in Fig. 1. The chemical formula of SrBi2Nb2O9 is (Bi2O2)(My−1NyO3y+1). M and N represent cations with low and high valances in the structure, respectively. The spatial structure of SrBi2Nb2O9 has two layers of perovskitelike TaO6 octahedron separated by Bi2O2 layers in the c-axis direction. Although the preparation and properties of SrBi2Nb2O9 thin films a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0377 2956
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 10, Oct 2004 Downloaded: 04 Apr 2015
have been investigated,9–12 the powder preparation and the reaction kinetics of SrBi2Nb2O9 formation have not been studied in detail. Understanding the preparation and reaction kinetics of SrBi2Nb2O9 powders is crucial for preparing targets with high chemical purity and high sintering density to produce high-quality thin films using physical vapor deposition techniques. In this study, SrBi2Nb2O9 powders were first synthesized using a new process employing BiNbO4 as a precursor, and the SrBi2Nb2O9 reaction kinetics were ex
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