Magnetic Ordering and Local Atomic Environments in Na0.67Fe1-yMnyO2-Cathode Materials for Na-Ion Batteries

R. Idczaka, K. Walczakb, R. Koniecznya, P. Sobotaa, c, W. Nowaka, c, V.H. Tranc aInstitute of Experimental Physics, University of Wrocław, pl. M. Borna 9, 50-204 Wrocław, Poland bFaculty of Energy and Fuels, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland cInstitute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-422 Wrocław, Poland

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The Na0.67Fe1-yMnyO2 (y=0.5 and 0.8) samples were investigated using 57Fe Mössbauer spectroscopy at temperatures ranging from 4.5 to 700 K and superconducting quantum interference device magnetometer at temperatures ranging from 2 to 300 K. It was found that both materials order antiferromagnetically below Néel temperature TN=9.5(5) K. Above this temperature, the samples exhibit a local-moment paramagnetism contributed from the Fe3+, Mn3+, and Mn4+ ions in high-spin state. The collected temperature-dependent Mössbauer spectra give clear evidence that they cannot be described using one component attributed to the iron atoms, which occupy only one crystallographic position in the hexagonal P63/mmc (P2-type) structure. The presence of the second component in all measured transmission Mössbauer spectroscopy spectra is ascribed to the highly distorted FeO6 octahedra, which are caused by a deficiency of Na atoms in the vicinity of the Mössbauer 57Fe probes. The Debye temperatures ΘpD=554(29) K (for y=0.5) and 437(42) K (for y=0.8) were obtained.

DOI:10.12693/APhysPolA.146.244 topics: Na-ion batteries, Mössbauer spectroscopy, magnetic ordering