title: First-order metal-insulator transition and infrared identification of shape-controlled magnetite nanocrystals.
abstract: The first-order metal-insulator transition (MIT) in magnetite has been known for a long time but is still controversial in its nature. In this study, well-defined magnetite nanocrystals (NCs) with controllable size, shape and terminated surface are first employed to elucidate this important issue, and new discoveries such as a highly suppressed phase transition temperature are identified by monitoring the variable-temperature electric resistance and infrared spectroscopy. Significantly, by carefully comparing the infrared vibrational bands of the as-prepared magnetite NCs with octahedral and cubic shapes, respectively, we found that these two forms of magnetite NCs exhibited different transmittance changes and frequency shifts of the infrared characteristics, presumably due to the differences in the lattice distortions on the corresponding {001} and {111}  terminal surfaces. This result produced evidence in support of the charge ordering of Fe atoms along the low dimensionality at octahedral B sites undergoing the MIT. Taken together, infrared identification was proposed to be an available characterization strategy for MIT, which can reflect more information on the elusive lattice distortion of crystallographic structure or exposed surfaces.
authors.affiliation: Department of Nanomaterials and Nanochemistry, Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui, People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: Zheng
authors.forename: Wei
authors.initials: W
authors.lastname: Su
authors.forename: Zeming
authors.initials: Z
authors.lastname: Qi
authors.forename: Yang
authors.initials: Y
authors.lastname: Xu
authors.forename: Min
authors.initials: M
authors.lastname: Zhou
authors.forename: Yi
authors.initials: Y
authors.lastname: Xie