Electrochemical, Magnetic, and Structural Investigation of the Lix(MnyFe1-y)PO4

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• 作者：Atsuo Yamada ; Yuki Takei ; Hiroshi Koizumi ; Noriyuki Sonoyama ; Ryoji Kanno ; Keiji Itoh ; Masao Yonemura ; and Takashi Kamiyama
• 刊名：Chemistry of Materials
• 出版年：2006
• 出版时间：February 7, 2006
• 年：2006
• 卷：18
• 期：3
• 页码：804 - 813
• 全文大小：421K
• 年卷期：v.18,no.3(February 7, 2006)
• ISSN：1520-5002

文摘

A series of synthetic heterosite-purpurite, (Mn_yFe_1-y)PO₄ (y < 0.8), with negligible disorder andimpurities, was obtained by chemical oxidation of the well-crystallized isotypic tryphillite-lithiophiliteseries, Li(Mn_yFe_1-y)PO₄ (ordered olivine structure, space group Pnma). Comparative magnetic and X-ray/neutron powder diffraction investigations of the two solid-solution lines were performed as a functionof Mn content to increase understanding of the electrochemical activity loss of Mn³⁺/Mn²⁺ in theLi_x(Mn_yFe_1-y)PO₄ electrode system. Introducing Mn ions into the 4c site did not cause significant changein the local geometry of M²⁺O₆ and PO₄ polyhedra, while the M³⁺O₆ octahedra became severely distortedwith an increase in the number of Jahn-Teller active Mn³⁺ ions. The edge-sharing geometry of M³⁺O₆and PO₄ polyhedra fixed the shared O3'-O3' interatomic distance, causing selective strong elongationof the M³⁺-O3' distance with small shrinkage of other M³⁺-O1, M³⁺-O2, and M³⁺-O3 bond lengths.The overall distortion of the MO₆ octahedra with M = Mn³⁺ was much larger than the correspondingchange in the unit-cell orthorombicity and significantly increased asymmetry in the M-O-Msuperexchange interaction. All samples exhibited antiferromagnetism; however, the trivalent series hadmore than a sevenfold larger decrease in Neel temperature T_N (from ca. 130 K at y = 0 to ca. 50 K aty = 0.8) compared to the divalent series (from ca. 52 K at y = 0 to ca. 35 K at y =1) as a function ofthe Mn content y.