I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[17273]
Open Access
Abstract: The mechanisms by which organisms control the stability of amorphous calcium carbonate (ACC) are yet not fully understood. Previous studies have shown that the intrinsic properties of ACC and its environment are critical in determining ACC stability. Here, the question, what is the effect of bulk incorporation versus surface adsorption of additives on the stability of synthetic ACC, is addressed. Using a wide range of in situ characterization techniques, it is shown that surface adsorption of poly(Aspartic acid) (pAsp) has a much larger stabilization effect than bulk incorporation of pAsp and only 1.5% pAsp could dramatically increase the crystallization temperature from 141 to 350 °C. On the contrary, surface adsorption of PO43− ions and OH− ions does not effectively stabilize ACC. However, bulk incorporation of these ions could significantly improve the ACC stability. It is concluded that the stabilization mechanism of pAsp is entirely different from that of PO43− and OH− ions: while pAsp is effectively inhibiting calcite nucleation at the surface of ACC particle, the latter acts to modify the ion mobility and delay crystal propagation. Thus, new insights on controlling the stability and crystallization processes of metastable amorphous materials are provided.
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Apr 2020
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I06-Nanoscience
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Weiwei
Li
,
Bonan
Zhu
,
Ruixue
Zhu
,
Qiang
Wang
,
Ping
Lu
,
Yuanwei
Sun
,
Clodomiro
Cafolla
,
Zhimin
Qi
,
Aiping
Chen
,
Peng
Gao
,
Haiyan
Wang
,
Qing
He
,
Kelvin H. L.
Zhang
,
Judith L.
Macmanus‐driscoll
Diamond Proposal Number(s):
[17284]
Open Access
Abstract: Control of BO6 octahedral rotations at the heterointerfaces of dissimilar ABO3 perovskites has emerged as a powerful route for engineering novel physical properties. However, its impact length scale is constrained at 2–6 unit cells close to the interface and the octahedral rotations relax quickly into bulk tilt angles away from interface. Here, a long‐range (up to 12 unit cells) suppression of MnO6 octahedral rotations in La0.9Ba0.1MnO3 through the formation of superlattices with SrTiO3 can be achieved. The suppressed MnO6 octahedral rotations strongly modify the magnetic and electronic properties of La0.9Ba0.1MnO3 and hence create a new ferromagnetic insulating state with enhanced Curie temperature of 235 K. The emergent properties in La0.9Ba0.1MnO3 arise from a preferential occupation of the out‐of‐plane Mn d 3z 2−r 2 orbital and a reduced Mn eg bandwidth, induced by the suppressed octahedral rotations. The realization of long‐range tuning of BO6 octahedra via superlattices can be applicable to other strongly correlated perovskites for exploring new emergent quantum phenomena.
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Aug 2020
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James
Byrne
,
Victoria
Coker
,
Eva
Cespedes
,
Paul L.
Wincott
,
David J.
Vaughan
,
Richard
Pattrick
,
Gerrit
Van Der Laan
,
Elke
Arenholz
,
Floriana
Tuna
,
Martin
Bencsik
,
Jonathan R.
Lloyd
,
Neil
Telling
Abstract: The magnetic moments of magnetite nanoparticles are dramatically enhanced through the addition of zinc in a microbiologically driven synthesis procedure. The particles are produced through the reduction of Fe(III)-compounds containing Zn(II) by the iron reducing bacterium Geobacter sulfurreducens .
Results indicate a signifi cant increase in the saturation magnetization by over 50% compared to magnetite at both room and low temperatures for relatively minor quantities of zinc substitution. A maximum saturation magnetization of nearly 100 emu g −1 of sample is measured at room temperature. Analysis of the cation site ordering reveals a complex dependence on the Zn content, with the combined effect of Zn substitution of Fe 3+ ions on tetrahedral sites, together with Fe 2+ cation oxidation, leading to the observed magnetization enhancement for low Zn doping levels. The improved magnetic properties give superior performance in MRI applications with an MRI contrast enhancement among the largest values reported, being more than 5 times larger than a commercial contrast agent (Feridex) measured under identical conditions.The synthesis technique applied here involves an environmentally benign route and offers the potential to tune the magnetic properties of magnetic
nanoparticles, with increased overall magnetization desirable for many different commercial applications.
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May 2014
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I06-Nanoscience
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Diamond Proposal Number(s):
[123]
Abstract: We report a novel microwave plasma enhanced chemical vapor deposition strategy for the efficient synthesis of multilayer graphene nanoflake films (MGNFs) on Si substrates. The constituent graphene nanoflakes have a highly graphitized knife-edge structure with a 2–3?nm thick sharp edge and show a preferred vertical orientation with respect to the Si substrate as established by near-edge X-ray absorption fine structure spectroscopy. The growth rate is approximately 1.6?µm min?1, which is 10 times faster than the previously reported best value. The MGNFs are shown to demonstrate fast electron-transfer (ET) kinetics for the Fe(CN)63?/4? redox system and excellent electrocatalytic activity for simultaneously determining dopamine (DA), ascorbic acid (AA) and uric acid (UA). Their biosensing DA performance in the presence of common interfering agents AA and UA is superior to other bare solid-state electrodes and is comparable only to that of edge plane pyrolytic graphite. Our work here, establishes that the abundance of graphitic edge planes/defects are essentially responsible for the fast ET kinetics, active electrocatalytic and biosensing properties. This novel edge-plane-based electrochemical platform with the high surface area and electrocatalytic activity offers great promise for creating a revolutionary new class of nanostructured electrodes for biosensing, biofuel cells and energy-conversion applications.
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Oct 2008
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Abstract: Combinatorial atmospheric pressure chemical vapor deposition (APCVD) is used to deposit anatase TiO2 with a graded level of F-doping between 1.10 ≤ F:Ti (at%) ≤ 2.57 from the reaction of titanium tetrachloride, ethyl acetate and trifluoroacetic acid at 500 °C on glass. The photocatalytic activity and electrical resistivity of 200 allotted positions across a grid are screened using high-throughput techniques. A blue region of film is singled out for containing the lowest electrical resistivities of any previously reported doped or undoped TiO2-based system formed by APCVD (ρ ≈ 0.22–0.45 Ω cm, n = 0.8–1.2 × 1018 cm−3, μ = 18–33 cm2 V−1 s−1). The blue region contains a lower fluorine doping level (F:Ti ≈ 1.1–1.6%, Ebg ≈ 3.06 eV) than its neighboring colorless region (F:Ti ≈ 2.3–2.6%, Ebg ≈ 3.15–3.21 eV, ρ ≈ 0.61–1.3 Ω cm). State-of-the-art hybrid density functional theory calculations were employed to elucidate the nature of the different doping behaviors. Two distinct fluorine doping environments were present. At low concentrations, F substituting for O (FO) dominates, forming blue F:TiO2. At high concentrations, negatively charged fluorine interstitials (Fi−1) begin to dominate, forming transparent F:TiO2.
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Mar 2014
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[14701]
Open Access
Abstract: Crystallizable, high-mobility conjugated polymers have been employed as secondary donor materials in ternary polymer solar cells in order to improve device efficiency by broadening their spectral response range and enhancing charge dissociation and transport. Here, contrasting effects of two crystallizable polymers, namely, PffBT4T-2OD and PDPP2TBT, in determining the efficiency improvements in PTB7-Th:PC71BM host blends are demonstrated. A notable power conversion efficiency of 11% can be obtained by introducing 10% PffBT4T-2OD (relative to PTB7-Th), while the efficiency of PDPP2TBT-incorporated ternary devices decreases dramatically despite an enhancement in hole mobility and light absorption. Blend morphology studies suggest that both PffBT4T-2OD and PDPP2TBT are well dissolved within the host PTB7-Th phase and facilitate an increased degree of phase separation between polymer and fullerene domains. While negligible charge transfer is determined in binary blends of each polymer mixture, effective energy transfer is identified from PffBT4T-2OD to PTB7-Th that contributes to an improvement in ternary blend device efficiency. In contrast, energy transfer from PTB7-Th to PDPP2TBT worsens the efficiency of the ternary device due to inefficient charge dissociation between PDPP2TBT and PC71BM.
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Dec 2017
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[9282]
Open Access
Abstract: A room temperature magnetoelectric multiferroic is of interest as, e.g., magnetoelectric random access memory. Bulk samples of the perovskite (1−x)BiTi(1−y)/2FeyMg(1−y)/2O3–xCaTiO3 (BTFM–CTO) are simultaneously ferroelectric, weakly ferromagnetic, and magnetoelectric at room temperature. In BTFM–CTO, the volatility of bismuth oxide, and the complex subsolidus reaction kinetics, cause the formation of a microscopic amount of ferrimagnetic spinel impurity, which complicates the quantitative characterization of their intrinsic magnetic and magnetoelectric properties. Here, a controlled synthesis route to single-phase bulk samples of BTFM–CTO is devised and their intrinsic properties are determined. For example, the composition x = 0.15, y = 0.75 shows a saturated magnetization of 0.0097μB per Fe, a linear magnetoelectric susceptibility of 0.19(1) ps m−1, and a polarization of 66 μC cm−2 at room temperature. The onset of weak ferromagnetism and linear magnetoelectric coupling are shown to coincide with the onset of bulk long-range magnetic order by neutron diffraction. The synthesis strategy developed here will be invaluable as the phase diagram of BTFM–CTO is explored further, and as an example for the synthesis of other compositionally complex BiFeO3-related materials.
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Feb 2016
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Zilu
Liu
,
Tianjun
Liu
,
Christopher N.
Savory
,
José P.
Jurado
,
Juan Sebastián
Reparaz
,
Jianwei
Li
,
Long
Pan
,
Charl F. J.
Faul
,
Ivan P.
Parkin
,
Gopinathan
Sankar
,
Satoru
Matsuishi
,
Mariano
Campoy‐quiles
,
David O.
Scanlon
,
Martijn A.
Zwijnenburg
,
Oliver
Fenwick
,
Bob C.
Schroeder
Open Access
Abstract: Organometallic coordination polymers (OMCPs) are a promising class of thermoelectric materials with high electrical conductivities and thermal resistivities. The design criteria for these materials, however, remain elusive and so far material modifications have been focused primarily on the nature of the metal cation to tune the thermoelectric properties. Herein, an alternative approach is described by synthesizing new organic ligands for OMCPs, allowing modulation of the thermoelectric properties of the novel OMCP materials over several orders of magnitude, as well as controlling the polarity of the Seebeck coefficient. Extensive material purification combined with spectroscopy experiments and calculations furthermore reveal the charge‐neutral character of the polymer backbones. In the absence of counter‐cations, the OMCP backbones are composed of air‐stable, ligand‐centered radicals. The findings open up new synthetic possibilities for OMCPs by removing structural constraints and putting significant emphasis on the molecular structure of the organic ligands in OMCP materials to tune their thermoelectric properties.
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Jun 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[1203]
Abstract: A range of optical probes are used to study the nanoscale-structure and electronic-functionality of a photovoltaic-applicable blend of the carbazole co-polymer poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3 '-benzothiadiazole) (PCDTBT) and the electronic accepting fullerene derivative (6,6)-phenyl C70-butyric acid methyl ester (PC70BM). In particular, it is shown that the glass transition temperature of a PCDTBT:PC70BM blend thin-film is not sensitive to the relative blend-ratio or film thickness (at 1:4 blending ratio), but is sensitive to casting solvent and the type of substrate on which it is deposited. It is found that the glass transition temperature of the blend reduces on annealing; an observation consistent with disruption of pp stacking between PCDTBT molecules. Reduced pp stacking is correlated with reduced hole-mobility in thermally annealed films. It is suggested that this explains the failure of such annealing protocols to substantially improve device-efficiency. The annealing studies demonstrate that the blend only undergoes coarse phase-separation when annealed at or above 155 degrees C, suggesting a promising degree of morphological stability of PCDTBT:PC70BM blends.
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Apr 2012
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B18-Core EXAFS
I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[16168, 16460]
Abstract: Perovskite‐like NaNbO3‐Bi1/3NbO3 solid solutions are studied to understand the interactions between octahedral rotations, which dominate the structural behavior of NaNbO3 and displacive disorder of Bi present in Bi1/3NbO3. Models of instantaneous structures for representative compositions are obtained by refining atomic coordinates against X‐ray total scattering and extended X‐ray‐absorption fine structure data, with additional input obtained from transmission electron microscopy. A mixture of distinct cations and vacancies on the cuboctahedral A‐sites in Na1−3x Bix NbO3 (x ≤ 0.2) results in 3D nanoscale modulations of structural distortions. This phenomenon is determined by the inevitable correlations in the chemical composition of adjacent unit cells according to the structure type—an intrinsic property of any nonmolecular crystals. Octahedral rotations become suppressed as x increases. Out‐of‐phase rotations vanish for x > 0.1, whereas in‐phase tilts persist up to x = 0.2, although for this composition their correlation length becomes limited to the nanoscale. The loss of out‐of‐phase tilting is accompanied by qualitative changes in the probability density distributions for Bi and Nb, with both species becoming disordered over loci offset from the centers of their respective oxygen cages. Symmetry arguments are used to attribute this effect to different strengths of the coupling between the cation displacements and out‐of‐phase versus in‐phase rotations. The displacive disorder of Bi and Nb combined with nanoscale clustering of lattice distortions are primarily responsible for the anomalous broadening of the temperature dependence of the dielectric constant.
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Jun 2020
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