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Espen Drath Bøjesen

Bio: Espen Drath Bøjesen is an academic researcher from Aarhus University. The author has contributed to research in topics: Hydrothermal synthesis & Crystallite. The author has an hindex of 18, co-authored 43 publications receiving 1050 citations. Previous affiliations of Espen Drath Bøjesen include Monash University & Monash University, Clayton campus.


Papers
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TL;DR: Adjustment of the synthesis temperature and precursor concentration not only allows control over nanoparticle size and morphology but also the structure, and particles as small as ~2 nm can be synthesized.
Abstract: The formation and growth mechanisms in the hydrothermal synthesis of SnO2 nanoparticles from aqueous solutions of SnCl4·5H2O have been elucidated by means of in situ X-ray total scattering (PDF) measurements. The analysis of the data reveals that when the tin(IV) chloride precursor is dissolved, chloride ions and water coordinate octahedrally to tin(IV), forming aquachlorotin(IV) complexes of the form [SnClx(H2O)6–x](4–x)+ as well as hexaaquatin(IV) complexes [Sn(H2O)6–y(OH)y](4–y)+. Upon heating, ellipsoidal SnO2 nanoparticles are formed uniquely from hexaaquatin(IV). The nanoparticle size and morphology (aspect ratio) are dependent on both the reaction temperature and the precursor concentration, and particles as small as ∼2 nm can be synthesized. Analysis of the growth curves shows that Ostwald ripening only takes place above 200 °C, and in general the growth is limited by diffusion of precursor species to the growing particle. The c-parameter in the tetragonal lattice is observed to expand up to 0.5% ...

171 citations

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TL;DR: The nucleation of pristine crystalline ceria nanoparticles originated from previously unknown cerium dimer complexes and the nanoparticle growth was highly accelerated under supercritical conditions.
Abstract: Supercritical growth: The formation and evolution of ceria nanoparticles during hydrothermal synthesis was investigated by in situ total scattering and powder diffraction. The nucleation of pristine crystalline ceria nanoparticles originated from previously unknown cerium dimer complexes. The nanoparticle growth was highly accelerated under supercritical conditions.

92 citations

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TL;DR: In this paper, in situ results obtained for ten different material systems, and show that nucleation of nanoparticles in solvothermal reactions expose a fascinating chemical richness spanning from mono-metal to complex polymer precursor species, which, through a specific system-dependent multistep reaction mechanism, develop into pristine nanocrystals.
Abstract: Nucleation phenomena are of critical importance in numerous areas of science and everyday life. For decades the prevailing models to explain nucleation have been based on thermodynamic arguments without consideration of the chemical nature of the specific system. Even though newer models have included system-dependent variables, the quantitative atomistic differences are largely ignored. As a consequence, nucleation processes are treated on a “particle” or “monomer” level without discussion of the true atomic scale “chemistry of nucleation”. In the past couple of years, in situ studies of solvothermal reactions have considerably changed the experimental insight into nucleation phenomena, and especially the measurement of X-ray total scattering data and the subsequent pair distribution function analysis have proven to be vital tools. Here we discuss in situ results obtained for ten different material systems, and show that nucleation of nanoparticles in solvothermal reactions expose a fascinating chemical richness spanning from mono-metal to complex polymer precursor species, which, through a specific system-dependent multistep reaction mechanism, develop into pristine nanocrystals. It is argued that it is time to introduce a paradigm shift in the general nucleation theory and move away from the “one model fits all” to a chemistry-based approach rooted in atomic scale insight.

85 citations

Journal ArticleDOI
TL;DR: In this article, the crystal structure and defect chemistry of hydrothermally synthesized LiFe1-xMnxPO4 (x = 0, 0.25, and 0.50) particles have been characterized by simultaneous neutron and X-ray Rietveld refinement as well as Xray and neutron pair distribution function (PDF) analysis, crystallinity determination, Mossbauer spectroscopy, ion coupled plasma (ICP) studies, and scanning electron microscopy (SEM).
Abstract: The crystal structure and defect chemistry of hydrothermally synthesized LiFe1-xMnxPO4 (x = 0, 0.25, and 0.50) particles have been characterized by simultaneous neutron and X-ray Rietveld refinement as well as X-ray and neutron pair distribution function (PDF) analysis, crystallinity determination, Mossbauer spectroscopy, ion coupled plasma (ICP) studies, and scanning electron microscopy (SEM). The very detailed structural refinements show that fast hydrothermal synthesis causes partial Fe-occupancy and vacancies on the Li (M1) site, while the Fe (M2) site is always fully occupied by iron. Thus, the defect is not merely a Li/Fe antisite defect, and excessive amounts of Fe are the origin of the disorder in the structure. Neutron and X-ray total scattering with PDF analysis show that after fast hydrothermal synthesis, the crystalline, defective LixFeyPO4 coexists with amorphous Li/Fe-PO4 structures having just short-range order. Iron excess is only seen in the crystalline part of the particles, and as the c...

81 citations

Journal ArticleDOI
06 Oct 2014-ACS Nano
TL;DR: The formation and growth of maghemite nanoparticles from ammonium iron(III) citrate solutions in hydrothermal synthesis conditions have been studied by in situ total scattering to identify the primary transformation from amorphous clusters to nanocrystallites.
Abstract: The formation and growth of maghemite (γ-Fe2O3) nanoparticles from ammonium iron(III) citrate solutions (C6O7H6·xFe3+·yNH4) in hydrothermal synthesis conditions have been studied by in situ total scattering. The local structure of the precursor in solution is similar to that of the crystalline coordination polymer [Fe(H2cit(H2O)]n, where corner-sharing [FeO6] octahedra are linked by citrate. As hydrothermal treatment of the solution is initiated, clusters of edge-sharing [FeO6] units form (with extent of the structural order <5 A). Tetrahedrally coordinated iron subsequently appears, and as the synthesis continues, the clusters slowly assemble into crystalline maghemite, giving rise to clear Bragg peaks after 90 s at 320 °C. The primary transformation from amorphous clusters to nanocrystallites takes place by condensation of the clusters along the corner-sharing tetrahedral iron units. The crystallization process is related to large changes in the local structure as the interatomic distances in the cluste...

70 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: Current research on materials is summarized and discussed and future directions for SIBs are proposed to provide important insights into scientific and practical issues in the development of S IBs.
Abstract: Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.

3,009 citations

Posted Content
TL;DR: The two-step solution-phase reactions to form hybrid materials of Mn(3)O(4) nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications should offer a new technique for the design and synthesis of battery electrodes based on highly insulating materials.
Abstract: We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

1,587 citations

Journal Article
TL;DR: In this article, the authors used in situ transmission electron microscopy to show that platinum nanocrystals can grow either by monomer attachment from solution onto the existing particles or by coalescence between the particles.
Abstract: It is conventionally assumed that the growth of monodisperse colloidal nanocrystals requires a temporally discrete nucleation followed by monomer attachment onto the existing nuclei. However, recent studies have reported violations of this classical growth model, and have suggested that inter-particle interactions are also involved during the growth. Mechanisms of nanocrystal growth still remain controversial. Using in situ transmission electron microscopy, we show that platinum nanocrystals can grow either by monomer attachment from solution onto the existing particles or by coalescence between the particles. Surprisingly, an initially broad size distribution of the nanocrystals can spontaneously narrow. We suggest that nanocrystals take different pathways of growth based on their size- and morphology-dependent internal energies. These observations are expected to be highly relevant for other nanocrystal systems.

949 citations