A neutron diffraction study and mode analysis of compounds of the system Lab>1?xb>Srb>xb>FeOb>3?xb>Fb>xb> (x=1, 0.8, 0.5, 0.2) and an investigation of their

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• 作者：Oliver Clemens ; Frank J. Berry ; Adrian J. Wright ; Kevin S. Knight ; J.M. Perez-Mato ; J.M. Igartua ; Peter R. Slater
• 关键词：Neutron diffraction ; Antiferromagnetism ; Perovskite ; Fluorination ; Iron
• 刊名：Journal of Solid State Chemistry
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：206
• 期：Complete
• 页码：158-169
• 全文大小：2375 K

文摘

We report here a detailed study of the system Lab>1?xb>Srb>xb>FeOb>3?xb>Fb>xb>, by neutron powder diffraction- and magnetic-measurements. All the compounds are robust antiferromagnetics with ordering temperatures well above room temperature. Magnetic moments are shown to align parallel to the c-axis. FC-ZFC measurements indicate a small canting of the magnetic moments, resulting in a ferromagnetic component with a maximum for Lab>0.5b>Srb>0.5b>FeOb>2.5b>Fb>0.5b>. We show that the system exhibits a composition-driven transition from a phase, for low fluorination levels (x¡Ü0.5), with Pnma symmetry and the usual system of octahedral tiltings, to a phase with space group Imma for higher fluorine contents, where a correlated distortion of the oxygen octahedra plays a significant role. The consistency of the structural models, with respect to the expected continuity of the amplitudes of the different distortion modes and the invariance of their internal form, was monitored through the symmetry mode decomposition of the structures.