Mechanosynthesized BiFeO3 Nanoparticles with Highly Reactive Surface and Enhanced Magnetization

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• 作者：Klebson L. Da Silva ; Dirk Menzel ; Armin Feldhoff ; Christian Ku虉bel ; Michael Bruns ; Andrea Paesano ; Jr. ; Andre Du虉vel ; Martin Wilkening ; Mohammad Ghafari ; Horst Hahn ; Fred J. Litterst ; Paul Heitjans ; Klaus D. Becker ; Vladimir S虒epela虂k
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：April 21, 2011
• 年：2011
• 卷：115
• 期：15
• 页码：7209-7217
• 全文大小：1096K
• 年卷期：v.115,no.15(April 21, 2011)
• ISSN：1932-7455

文摘

A one-step synthesis of nanostructured bismuth ferrite (BiFeO₃) via mechanochemical processing of a 伪-Fe₂O₃/Bi₂O₃ mixture at room temperature is reported. The mechanically induced phase evolution of the mixture is followed by XRD and ⁵⁷Fe M枚ssbauer spectroscopy. It is shown that the mechanosynthesis of the rhombohedrally distorted perovskite BiFeO₃ phase is completed after 12 h. Compared to the traditional synthesis route, the mechanochemical process used here represents a one-step, high-yield, low-temperature, and low-cost procedure for the synthesis of BiFeO₃. High-resolution TEM and XRD studies reveal a nonuniform structure of mechanosynthesized BiFeO₃ nanoparticles consisting of a crystalline core surrounded by an amorphous surface shell. The latter is found to exhibit an extraordinarily high metastability causing a rapid crystallization of nanoparticles under irradiation with electrons. In situ high-resolution TEM observations of the crystallization clearly show that the heterogeneous processes of nucleation and growth of bismuth iron oxide crystallites are spatially confined to the amorphous surface regions. This fact provides access to the elucidation of the mechanism of mechanosynthesis. It is demonstrated that the mechanosynthesized ferrite nanoparticles exhibit a partial superparamagnetism at room temperature. Quantitative information on the short-range structure and hyperfine interactions, provided by the nuclear spectroscopic technique, is complemented by an investigation of the magnetic behavior of nanostructured BiFeO₃ on a macroscopic scale by means of SQUID technique. As a consequence of canted spins in the surface shell of nanoparticles, the mechanosynthesized BiFeO₃ exhibits an enhanced magnetization, an enhanced coercivity, and a shifted hysteresis loop.