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• 作者：Tao Yang ; Mark Croft ; Alexander Ignatov ; Israel Nowik ; Rihong Cong ; Martha Greenblatt
• 刊名：Chemistry of Materials
• 出版年：2010
• 出版时间：November 9, 2010
• 年：2010
• 卷：22
• 期：21
• 页码：5876-5886
• 全文大小：1285K
• 年卷期：v.22,no.21(November 9, 2010)
• ISSN：1520-5002

文摘

Solid solutions of Ca_1−δFe_2−xMn_xO₄ (0.45 ≤ x ≤ 2) were synthesized from CaCl₂ as flux at 850 °C in air. The entire series, even with x = 2, crystallizes in the CaFe₂O₄-type structure (Pnma), rather than in the CaMn₂O₄-type structure (Pbcm). Rietveld refinements confirmed mixed-valency Mn³⁺/Mn⁴⁺ and a substantial level of Ca²⁺ deficiency (δ ≈ 0.25) at high x. With increasing x, the unit-cell dimensions a and b decrease, while that of c increases. Detailed structural analyses, together with Mn K-edge X-ray absorption and ⁵⁷Fe Mssbauer spectroscopy studies, revealed that the stabilization of CaFe₂O₄-type structure, even at high values of x, is due to the existence of non-Jahn−Teller active Mn⁴⁺ (and Fe³⁺), which is compensated by the formation of the Ca²⁺ deficiencies in the one-dimensional (1D) channels of Ca_1−δFe_2−xMn_xO₄ during the flux synthesis. Antiferromagnetic (AFM) long-range ordering is achieved for all compounds at low temperature, because of strong AFM interactions between Mn³⁺/Mn⁴⁺ and Fe³⁺. In addition, a spin (or cluster) glass component was also observed, as expected, because of the extensive Mn/Fe structural and Mn³⁺/Mn⁴⁺ charge disordering.