Single Crystalline La0.7Sr0.3MnO3 Molecular Sieve Nanowires with High Temperature Ferromagnetism

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• 作者：Adri谩n Carretero-Genevrier ; Jaume G谩zquez ; Juan Carlos Idrobo ; Judith Or贸 ; Jordi Arbiol ; Mar铆a Varela ; Etienne Ferain ; Juan Rodr铆guez-Carvajal ; Teresa Puig ; Narc铆s Mestres ; Xavier Obradors
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：March 23, 2011
• 年：2011
• 卷：133
• 期：11
• 页码：4053-4061
• 全文大小：1223K
• 年卷期：v.133,no.11(March 23, 2011)
• ISSN：1520-5126

文摘

Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO₂ and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates. Because of the confined nucleation in high aspect ratio nanopores and of the high temperatures attained, new structures with novel physical properties have been produced. During the calcination process, the nucleation and crystallization of 蔚-MnO₂ nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 渭m long and flexible hexagonal nanowires at mild growth temperatures (T_g = 700 掳C) as a consequence of the large crystallographic anisotropy of 蔚-MnO₂. The nanocrystallites of MnO₂ formed at low temperatures serve as seeds for the growth of La_0.7Sr_0.3MnO₃ nanowires at growth temperatures above 800 掳C, through the diffusion of La and Sr into the empty 1D-channels of 蔚-MnO₂. Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 脳 4) monoclinic nanowires with composition La_0.7Sr_0.3MnO₃ and with ordered arrangement of La³⁺ and Sr²⁺ cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T_c > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.