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Xing W, Zhang Y, Cui J, Liang S, Meng F, Zhu J, Yu R. Atomic structures of twin boundaries in CoO. Phys Chem Chem Phys 2021; 23:25590-25596. [PMID: 34783799 DOI: 10.1039/d1cp04112f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The twinning plane of crystals with a face-centered-cubic (FCC) structure is usually the (111) plane, as found in FCC metals and oxides with FCC sublattices of oxygen, like rock-salt-type NiO and spinel-type Fe3O4. Surprisingly, we found in this work that the twinning plane of rock-salt-type CoO is the (112) plane, although Co is adjacent to Ni in the periodic table. The atomic and electronic structures of the CoO(112) twin boundary with in-plane shift vector 1/2[111] have been studied combining aberration-corrected scanning transmission electron microscopy (STEM), electron-energy-loss spectroscopy (EELS), and density functional theory (DFT) calculations. It was found that the atoms at the twin boundary have nominal oxidation states, and the twin boundary remains insulating and antiferromagnetically coupled. Importantly, through the electronic structures and the crystal orbital Hamilton population (COHP) analyses, the (112) twin boundary is found to be more stable than the (111) twin boundary.
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Affiliation(s)
- Wandong Xing
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, Key Laboratory of Advanced Materials of Ministry of Education of China, State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China.
| | - Yang Zhang
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, Key Laboratory of Advanced Materials of Ministry of Education of China, State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China.
| | - Jizhe Cui
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, Key Laboratory of Advanced Materials of Ministry of Education of China, State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China.
| | - Shiyou Liang
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, Key Laboratory of Advanced Materials of Ministry of Education of China, State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China.
| | - Fanyan Meng
- Department of Physics, University of Science and Technology Beijing, Beijing 100083, China.
| | - Jing Zhu
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, Key Laboratory of Advanced Materials of Ministry of Education of China, State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China.
| | - Rong Yu
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, Key Laboratory of Advanced Materials of Ministry of Education of China, State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China.
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Plummer LK, Hutchison JE. Understanding the Effects of Iron Precursor Ligation and Oxidation State Leads to Improved Synthetic Control for Spinel Iron Oxide Nanocrystals. Inorg Chem 2020; 59:15074-15087. [PMID: 33006469 DOI: 10.1021/acs.inorgchem.0c02040] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Iron oxide nanocrystals have the potential for use in a wide variety of applications if we can finely control and tune the diverse structural attributes that lead to specific, desired properties. At the high temperatures utilized for thermal decomposition based syntheses, commonly used Fe(III) alkylcarboxylate precursors are inadvertently reduced and produce wüstite (FeO), which is paramagnetic, as opposed to the desired ferrimagnetic spinel phases of magnetite (Fe3O4) and maghemite (γ-Fe2O3). To circumvent this issue, we carried out syntheses at lower temperatures (∼230 °C) using an esterification-mediated approach. Under these conditions, formation of the FeO phase can be avoided. However, we found that the precursor oxidation state and ligation had a surprisingly strong influence on the morphologies of the resulting nanocrystals. To investigate the cause of these morphological effects, we carried out analogous nanocrystal syntheses with a series of precursors. The use of Fe(III) oleate precursors yielded highly crystalline, largely twin-free nanocrystals; however, small amounts of acetylacetonate ligation yielded nanocrystals with morphologies characteristic of twin defects. During synthesis at 230 °C, the Fe(III) oleate precursor is partially reduced, providing sufficient quantities of Fe(II) that are needed to grow the Fe3O4 nanocrystals (wherein one-third of the iron atoms are in the Fe(II) state) without twinning. Our investigations suggest that the acetylacetonate ligands prevent reduction of Fe(III) to Fe(II), leading to twinned structures during synthesis. Harnessing this insight, we identified conditions to predictably and continuously grow octahedral, spinel nanocrystals as well as conditions to synthesize highly twinned nanocrystals. These findings also help explain observations in the thermal decomposition synthesis literature which suggest that iron oxide nanocrystals produced from Fe(acac)3 are less prone to FeO contamination in comparison to those produced from Fe(III) alkylcarboxylates.
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Affiliation(s)
- L Kenyon Plummer
- Department of Chemistry and Biochemistry and Materials Science Institute, University of Oregon, Eugene, Oregon 97403, United States
| | - James E Hutchison
- Department of Chemistry and Biochemistry and Materials Science Institute, University of Oregon, Eugene, Oregon 97403, United States
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Bhattacharjee S, Banerjee A, Mazumder N, Chanda K, Sarkar S, Chattopadhyay KK. Negative capacitance switching in size-modulated Fe 3O 4 nanoparticles with spontaneous non-stoichiometry: confronting its generalized origin in non-ferroelectric materials. NANOSCALE 2020; 12:1528-1540. [PMID: 31854416 DOI: 10.1039/c9nr07902e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Persistent low-frequency negative capacitance (NC) dispersion has been detected in half-metallic polycrystalline magnetite (Fe3O4) nanoparticles with varying sizes from 13 to 236 nm under the application of moderate dc bias. Using the Havriliak-Negami model, 3D Cole-Cole plots were employed to recapitulate the relaxation times (τ) of the associated oscillating dipoles, related shape parameters (α, β) and resistivity for the nanoparticles with different sizes. The universal Debye relaxation (UDR) theory requires a modification to address the shifted quasi-static NC-dispersion plane in materials showing both +ve and -ve capacitances about a transition/switching frequency (f0). A consistent blue-shift in 'f0' is observed with increasing external dc field and decreasing particle size. Based on this experimental data, a generalized dispersion scheme is proposed to fit the entire positive and negative capacitance regime, including the diverging transition point. In addition, a comprehensive model is discussed using phasor diagrams to differentiate the underlying mechanisms of the continuous transition from -ve to +ve capacitance involving localized charge recombination or time-dependent injection/displacement currents, which has been adequately explored in the scientific literature, and the newly proposed 'capacitive switching' phenomenon. An inherent non-stoichiometry due to iron vacancies [Fe3(1-δ)O4], duly validated from first principles calculations, builds up p-type nature, which consequently promotes more covalent and heavier dipoles and slows the dipolar relaxations; this is incommensurate with Maxwell-Wagner interfacial polarization (MWIP) dynamics. This combinatorial effect is likely responsible for the sluggish response of the associated dipoles and the stabilization of NC.
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Chen C, Li H, Seki T, Yin D, Sanchez-Santolino G, Inoue K, Shibata N, Ikuhara Y. Direct Determination of Atomic Structure and Magnetic Coupling of Magnetite Twin Boundaries. ACS NANO 2018; 12:2662-2668. [PMID: 29480718 DOI: 10.1021/acsnano.7b08802] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Clarifying how the atomic structure of interfaces/boundaries in materials affects the magnetic coupling nature across them is of significant academic value and will facilitate the development of state-of-the-art magnetic devices. Here, by combining atomic-resolution transmission electron microscopy, atomistic spin-polarized first-principles calculations, and differential phase contrast imaging, we conduct a systematic investigation of the atomic and electronic structures of individual Fe3O4 twin boundaries (TBs) and determine their concomitant magnetic couplings. We demonstrate that the magnetic coupling across the Fe3O4 TBs can be either antiferromagnetic or ferromagnetic, which directly depends on the TB atomic core structures and resultant electronic structures within a few atomic layers. Revealing the one-to-one correspondence between local atomic structures and magnetic properties of individual grain boundaries will shed light on in-depth understanding of many interesting magnetic behaviors of widely used polycrystalline magnetic materials, which will surely promote the development of advanced magnetic materials and devices.
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Affiliation(s)
- Chunlin Chen
- Shenyang National Laboratory for Materials Science , Institute of Metal Research, Chinese Academy of Sciences , Shenyang 110016 , China
- Advanced Institute for Materials Research , Tohoku University , 2-1-1 Katahira , Aoba-ku, Sendai 980-8577 , Japan
| | - Hongping Li
- Advanced Institute for Materials Research , Tohoku University , 2-1-1 Katahira , Aoba-ku, Sendai 980-8577 , Japan
- Institute for Advanced Materials, School of Materials Science and Engineering , Jiangsu University , Zhenjiang 212013 , China
| | - Takehito Seki
- Institute of Engineering Innovation , The University of Tokyo , 2-11-16 Yayoi , Bunkyo-ku, Tokyo 113-8656 , Japan
| | - Deqiang Yin
- Advanced Institute for Materials Research , Tohoku University , 2-1-1 Katahira , Aoba-ku, Sendai 980-8577 , Japan
- College of Aerospace Engineering , Chongqing University , Chongqing 400044 , China
| | - Gabriel Sanchez-Santolino
- Institute of Engineering Innovation , The University of Tokyo , 2-11-16 Yayoi , Bunkyo-ku, Tokyo 113-8656 , Japan
| | - Kazutoshi Inoue
- Advanced Institute for Materials Research , Tohoku University , 2-1-1 Katahira , Aoba-ku, Sendai 980-8577 , Japan
| | - Naoya Shibata
- Institute of Engineering Innovation , The University of Tokyo , 2-11-16 Yayoi , Bunkyo-ku, Tokyo 113-8656 , Japan
| | - Yuichi Ikuhara
- Advanced Institute for Materials Research , Tohoku University , 2-1-1 Katahira , Aoba-ku, Sendai 980-8577 , Japan
- Institute of Engineering Innovation , The University of Tokyo , 2-11-16 Yayoi , Bunkyo-ku, Tokyo 113-8656 , Japan
- Nanostructures Research Laboratory , Japan Fine Ceramics Center , 2-4-1 Mutsuno , Atsuta, Nagoya 456-8587 , Japan
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Nedelkoski Z, Kepaptsoglou D, Ghasemi A, Achinuq B, Hasnip PJ, Yamada S, Hamaya K, Ramasse QM, Hirohata A, Lazarov VK. Controlling the half-metallicity of Heusler/Si(1 1 1) interfaces by a monolayer of Si-Co-Si. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:395003. [PMID: 27501822 DOI: 10.1088/0953-8984/28/39/395003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co2(Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si-Co-Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si. We show that such a layer is energetically favourable to exist at the interface. This was further confirmed by direct observations of CoSi2 nano-islands at the interface, by employing atomic resolution scanning transmission electron microscopy.
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Affiliation(s)
- Zlatko Nedelkoski
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | | | - Arsham Ghasemi
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Barat Achinuq
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Philip J Hasnip
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Shinya Yamada
- Department of Systems Innovation, Osaka University, Osaka 560-8531, Japan
| | - Kohei Hamaya
- Department of Systems Innovation, Osaka University, Osaka 560-8531, Japan
| | - Quentin M Ramasse
- SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK
| | | | - Vlado K Lazarov
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
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Lai CC, Lo CY, Nguyen DH, Huang JZ, Tsai WS, Ma YR. Atomically smooth hybrid crystalline-core glass-clad fibers for low-loss broadband wave guiding. OPTICS EXPRESS 2016; 24:20089-20106. [PMID: 27607618 DOI: 10.1364/oe.24.020089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We demonstrate direct evidence for the first realization of atomically smooth sapphire crystalline fiber cores with a surface variation of only ~1.9 Å. The hybrid glass-clad crystalline cores were grown by a laser-based fiber drawing technique. Because of the improvement in crystal fiber quality, we were able, for the first time, to comprehensively and quantitatively elucidate the correlation between fiber nanostructure and optical loss. We also experimentally demonstrated that high-temperature treatment has a significant impact on defect relaxation and promotes excellent crystallinity, and hence enables low-loss optical wave guiding. The experimentally measured propagation losses in the order of 0.01-0.1 dB/cm are the lowest ever reported among conventional Ti:sapphire channel waveguides and ultrafast-laser-inscribed waveguides, and agree well with the theory. Through experiments and numerical calculation, we have demonstrated that low threshold and high efficiency of Ti:sapphire crystal fiber lasers are possible with the atomic-level roughness, low-loss propagation, and high crystallinity of the Ti:sapphire crystalline core.
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Polar Spinel-Perovskite Interfaces: an atomistic study of Fe3O4(111)/SrTiO3(111) structure and functionality. Sci Rep 2016; 6:29724. [PMID: 27411576 PMCID: PMC4944391 DOI: 10.1038/srep29724] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 06/21/2016] [Indexed: 11/09/2022] Open
Abstract
Atomic resolution scanning transmission electron microscopy and electron energy loss spectroscopy combined with ab initio electronic calculations are used to determine the structure and properties of the Fe3O4(111)/SrTiO3(111) polar interface. The interfacial structure and chemical composition are shown to be atomically sharp and of an octahedral Fe/SrO3 nature. Band alignment across the interface pins the Fermi level in the vicinity of the conduction band of SrTiO3. Density functional theory calculations demonstrate very high spin-polarization of Fe3O4 in the interface vicinity which suggests that this system may be an excellent candidate for spintronic applications.
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