On the observation of a huge lattice contraction and crystal habit modifications in LiMn₂O₄ prepared by a fuel assisted solution combustion

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• 作者：K. Ragavendran ; D. Sherwood ; D. Vasudevan ; Bosco Emmanuel
• 关键词：Mixed valence ; Lithium manganate ; Lattice contraction ; Crystal shape algorithm ; Crystal habit ; Poly vinyl alcohol ; Geo physics
• 刊名：Physica B
• 出版年：2009
• 出版时间：1 August 2009
• 年：2009
• 卷：404
• 期：16
• 页码：2166-2171
• 全文大小：430 K

文摘

Two batches of poly-crystalline lithium manganate were prepared by a fuel assisted solution combustion method. LiMn₂O₄(S) was prepared using starch as the fuel and LiMn₂O₄(P) was prepared using poly vinyl alcohol (PVA) as the fuel. XRD studies indicated a significant and consistent shift in the 2θ values of all the hkl peaks to higher values in LiMn₂O₄(P) compared to LiMn₂O₄(S) indicating a lattice contraction in the former. TG/DTA studies indicated a higher formation temperature (25 °C higher) for LiMn₂O₄(P). The higher formation temperature most likely promotes the oxidation of some Mn³⁺ to Mn⁴⁺ with a lower ionic radius causing a lattice contraction. This hypothesis is confirmed through XPS studies which indicated the presence of a higher fraction of Mn⁴⁺ in LiMn₂O₄(P) than that present in LiMn₂O₄(S). A crystal shape algorithm was used to generate the crystal habits of lithium manganate from their XRD data leading to an understanding on the exposed hkl planes in these materials. From the atomic arrangement on the exposed hkl planes it is predicted that LiMn₂O₄(P) would be less prone to manganese dissolution and hence would possess a higher cycle life when compared to LiMn₂O₄(S).