Density Functional Theory-Based Bond Pathway Decompositions of Hyperfine Shifts: Equipping Solid-State NMR to Characterize Atomic Environments in Paramagnetic Materials

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• 作者：Derek S. Middlemiss ; Andrew J. Ilott ; Rapha毛le J. Cl茅ment ; Fiona C. Strobridge ; Clare P. Grey
• 刊名：Chemistry of Materials
• 出版年：2013
• 出版时间：May 14, 2013
• 年：2013
• 卷：25
• 期：9
• 页码：1723-1734
• 全文大小：496K
• 年卷期：v.25,no.9(May 14, 2013)
• ISSN：1520-5002

文摘

Solid-state nuclear magnetic resonance (NMR) of paramagnetic samples has the potential to provide a detailed insight into the environments and processes occurring in a wide range of technologically-relevant phases, but the acquisition and interpretation of spectra is typically not straightforward. Structural complexity and/or the occurrence of charge or orbital ordering further compound such difficulties. In response to such challenges, the present article outlines how the total Fermi contact (FC) shifts of NMR observed centers (OCs) may be decomposed into sets of pairwise metal鈥揙C bond pathway contributions via solid-state hybrid density functional theory calculations. A generally applicable 鈥渟pin flipping鈥?approach is outlined wherein bond pathway contributions are obtained by the reversal of spin moments at selected metal sites. The applications of such pathway contributions in interpreting the NMR spectra of structurally and electronically complex phases are demonstrated in a range of paramagnetic Li-ion battery positive electrodes comprising layered LiNiO₂, LiNi_0.125Co_0.875O₂, and LiCr_0.125Co_0.875O₂ oxides; and olivine-type LiMPO₄ and MPO₄ (M = Mn, Fe, and Co) phosphates. The FC NMR shifts of all ^6/7Li and ³¹P sites are decomposed, providing unambiguous NMR-based proof of the existence of local Ni³⁺-centered Jahn鈥揟eller distortions in LiNiO₂ and LiNi_0.125Co_0.875O₂, and showing that the presence of M²⁺/M³⁺ solid solutions and/or M/M鈥?isovalent transition metal (TM) mixtures in the olivine-type electrodes should lead to broad and potentially interpretable NMR spectra. Clear evidence for the presence of a dynamic Jahn鈥揟eller distortion is obtained for LiNi_xCo_1鈥?i>xO₂. The results emphasize the utility of solid-state NMR in application to TM-containing battery materials and to paramagnetic samples in general.

Keywords:

paramagnetism; disorder; nuclear magnetic resonance; density functional theory; hyperfine interactions; Fermi contact; transition metals; Jahn鈭扵eller effect; energy materials; batteries; electrode phases