Structures and Magnetism of the Rare-Earth Orthochromite Perovskite Solid Solution LaxSm1鈥?i>xCrO3

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• 作者：Luke M. Daniels ; Mads. C. Weber ; Martin R. Lees ; Mael Guennou ; Reza J. Kashtiban ; Jeremy Sloan ; Jens Kreisel ; Richard I. Walton
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：October 21, 2013
• 年：2013
• 卷：52
• 期：20
• 页码：12161-12169
• 全文大小：481K
• 年卷期：v.52,no.20(October 21, 2013)
• ISSN：1520-510X

文摘

A new mixed rare-earth orthochromite series, La_xSm_1鈥?i>xCrO₃, prepared through single-step hydrothermal synthesis is reported. Solid solutions (x = 0, 0.25, 0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by the hydrothermal treatment of amorphous mixed-metal hydroxides at 370 掳C for 48 h. Transmission electron microscopy (TEM) reveals the formation of highly crystalline particles with dendritic-like morphologies. Rietveld refinements against high-resolution powder X-ray diffraction (PXRD) data show that the distorted perovskite structures are described by the orthorhombic space group Pnma over the full composition range. Unit cell volumes and Cr鈥揙鈥揅r bond angles decrease monotonically with increasing samarium content, consistent with the presence of the smaller lanthanide in the structure. Raman spectroscopy confirms the formation of solid solutions, the degree of their structural distortion. With the aid of shell-model calculations the complex mixing of Raman modes below 250 cm^鈥? is clarified. Magnetometry as a function of temperature reveals the onset of low-temperature antiferromagnetic ordering of Cr³⁺ spins with weak ferromagnetic component at N茅el temperatures (T_N) that scale linearly with unit cell volume and structural distortion. Coupling effects between Cr³⁺ and Sm³⁺ ions are examined with enhanced susceptibilities below T_N due to polarization of Sm³⁺ moments. At low temperatures the Cr³⁺ sublattice is shown to undergo a second-order spin reorientation observed as a rapid decrease of susceptibility.