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.
Nanotechnology. 2011 Dec 2;22(48):485706. doi: 10.1088/0957-4484/22/48/485706. Epub 2011 Nov 9.
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.
很久以来，人们一直都知道磁铁矿中的一级金属-绝缘体转变（MIT），但其本质仍存在争议。在这项研究中，我们首次采用具有可控尺寸、形状和终止表面的规则磁铁矿纳米晶体（NC）来阐明这一重要问题，并通过监测变温电阻和红外光谱，发现了相变温度被高度抑制等新发现。值得注意的是，通过仔细比较所制备的八面体和立方体形磁铁矿 NCs 的红外振动带，我们发现这两种形式的磁铁矿 NCs 表现出不同的红外特征透过率变化和频移，这可能归因于相应的{001}和{111}端面上的晶格畸变差异。这一结果为 Fe 原子在八面体 B 位沿低维方向的电荷有序化导致 MIT 提供了证据。总的来说，红外识别被提议作为 MIT 的一种可行的表征策略，它可以反映出晶体结构或暴露表面的难以捉摸的晶格畸变的更多信息。
