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.

Gold-decorated magnetic nanoparticles design for hyperthermia applications and as a potential platform for their surface-functionalization

“…The small bump observed in the FC branch at the same temperature supports this interpretation. The shift of the Verwey transition to lower temperatures has been already reported in Fe 3 O 4 NPs with sizes smaller than ≈15 nm, and attributed to size 34 or shape 35 effects. The origin of the second bump at T 1 ≈ 45 K is not clear and might be related to thermal relaxation/unblocking processes of the smallest Fe 3 O 4 (<10 nm) cores observed in TEM images, which is consistent also with the increase of the FC curves at low temperatures due to weak inter-particle interactions of small particles.

Figure 2( a ) DC magnetization curves obtained in zero-field-cooled (ZFC, lower branch) and field-cooled (H FC = 2.39 kA/m, upper branch) modes for PEI-Fe 3 O 4 (filled black circles) and Au@PEI-Fe 3 O 4 (open red circles) NPs.

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Laser Processed Antimicrobial Nanocomposite Based on Polyaniline Grafted Lignin Loaded with Gentamicin-Functionalized Magnetite

“…Such a phenomenon is related to the grafting process and the formation of binary blends between PANI and LIG, due to the successful interaction of lignin with the conductive polyaniline through their hydroxyl and carbonyl groups. However, the MAPLE processed PANI-LIG coating presents similar infrared maxima as in the case of DC specimen, the identified absorption peaks being in good accordance with the results described in the literature for PANI-based materials [55,56].…”

Ultrathin Nanosheets of Half‐Metallic Monoclinic Vanadium Dioxide with a Thermally Induced Phase Transition

“…However, the traditional variable‐temperature XRD, differential scanning calorimetry (DSC), and resistance measurements for identification of the insulator‐to‐metal transition (IMT) accompanied with SPT are only performed on the bulk sample 27. Fortunately, the far‐IR spectroscopy with the advantage of excluding the influence of the grain boundaries provides sensitive spectral response to the intrinsic lattice vibrations during the phase transition of finite‐sized nanomaterials 28. 29 As shown in Figure 4, we found that, for both of the nanosheet and the bulk, the IR transmittance shows strong steplike peaks (ca.…”