Recent Highlights

 

Charge-ordering transition in iron oxide Fe4O5 involving competing dimer and trimer formation

Phase transitions that occur in materials, driven, for instance, by changes in temperature or pressure, can dramatically change the materials’ properties. Discovering new types of transitions and understanding their mechanisms is important not only from a fundamental perspective, but also for practical applications. Here we investigate a recently discovered Fe4O5 that adopts an orthorhombic CaFe3O5-type crystal structure that features linear chains of Fe ions. On cooling below ∼150 K, Fe4O5 undergoes an unusual charge-ordering transition that involves competing dimeric and trimeric ordering within the chains of Fe ions. This transition is concurrent with a significant increase in electrical resistivity. Magnetic-susceptibility measurements and neutron diffraction establish the formation of a collinear antiferromagnetic order above room temperature and a spin canting at 85 K that gives rise to spontaneous magnetization. We discuss possible mechanisms of this transition and compare it with the trimeronic charge ordering observed in magnetite below the Verwey transition temperature.

Nature Chemistry, 2016

 

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B,C, Examples of reciprocal lattices of X-ray diffraction intensities at 260 K (B) and 100 K (C). a* and b* are the axes of reciprocal lattices.

Mechanistic Studies as a Tool for the Design of Copper-Based Heterostructures

Under control of X-rays, the composition of copper heterostructures can be precisely tuned on a scale spanning from that of an individual heterojunction to the macroscale. This is achieved via in situ powder X-ray diffraction studies and facilitates their technological application.

Advanced Materials Interfaces, 2015

 

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Superionic Conduction of Sodium and Lithium in Anion-Mixed Hydroborates Na3BH4B12H12 and (Li0.7Na0.3)3BH4B12H12

Novel mixed-anion compounds Na3BH4B12H12 and (Li0.7Na0.3)3BH4B12H12 show superionic conduction corresponding to highly disordered cations and continuous migration paths in the structure. Na-rich Na3BH4B12H12 with a room-temperature conductivity of 0.5 × 10−3 S cm−1 provides a light-weight solution for the electrolyte in Na-based, all solid-state batteries. (Li0.7Na0.3)3BH4B12H12 favors ionic conductivity for both Li and Na cations, but only above 500 K.

Advanced Energy Materials, 2015

 

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Structure and properties of complex hydride perovskite materials

Perovskite materials host an incredible variety of functionalities. Although the lightest element, hydrogen, is rarely encountered in oxide perovskite lattices, it was recently observed as the hydride anion H−, substituting for the oxide anion in ​BaTiO3. Here we present a series of 30 new complex hydride perovskite-type materials, based on the non-spherical ​tetrahydroborate anion ​BH4− and new synthesis protocols involving rare-earth elements. Photophysical, electronic and ​hydrogen storage properties are discussed, along with counterintuitive trends in structural behaviour. The electronic structure is investigated theoretically with density functional theory solid-state calculations. BH4-specific anion dynamics are introduced to perovskites, mediating mechanisms that freeze lattice instabilities and generate supercells of up to 16 × the unit cell volume in AB(BH4)3. In this view, homopolar hydridic di-hydrogen contacts arise as a potential tool with which to tailor crystal symmetries, thus merging concepts of molecular chemistry with ceramic-like host lattices. Furthermore, anion mixing ​BH4−←X− (X−=Cl−, Br−, I−) provides a link to the known ABX3 halides.

 

Nature Communications, 2014
 

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The origin of antiferroelectricity in PbZrO3

Antiferroelectrics are essential ingredients for the widely applied piezoelectric and ferroelectric materials. Despite their technological importance, the reason why materials become antiferroelectric has remained allusive since their first discovery. Tagantsev et al. performed an exhaustive study of the phenomena by means of synchrotron radiation inelastic and diffuse scattering - 2 techniques being intensively developed right now. The analysis reveals that the paraelectric to antiferroelectric phase transition is driven by the softening of a single lattice mode via flexoelectric coupling. These findings resolve the mystery of the origin of antiferroelectricity in lead zirconate and suggest an approach to treat other complex phase transitions in ferroics.

 

Nature Communications, 2013
 

Distributions of the diffuse scattering intensity at 550 K.

 

Giant negative linear compressibility in zinc dicyanoaurate

The counterintuitive phenomenon of negative linear compressibility (NLC) is a highly desirable but rare property exploitable in the development of artificial muscles, actuators and next-generation pressure sensors. In all cases, material performance is directly related to the magnitude of intrinsic NLC response. Here we show the molecular framework material zinc(II) dicyanoaurate(I), Zn[Au(CN)2]2, exhibits the most extreme and persistent NLC behaviour yet reported: under increasing hydrostatic pressure its crystal structure expands in one direction at a rate that is an order of magnitude greater than both the typical contraction observed for common engineering materials and also the anomalous expansion in established NLC candidates. This extreme behaviour arises from the honeycomb-like structure of Zn[Au(CN)2]2 coupling volume reduction to uniaxial expansion, and helical Au…Au ‘aurophilic’ interactions accommodating abnormally large linear strains by functioning as supramolecular springs.

Nature Materials, 2013
 
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Design of zeolite by inverse sigma transformation

Although the search for new zeolites has traditionally been based on trial and error, more rational methods are now available. The theoretical concept of inverse σ transformation of a zeolite framework to generate a new structure by removal of a layer of framework atoms and contraction has for the first time been achieved experimentally.



Nature Materials, 2012
 
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Features of the secondary structure of a protein molecule from

powder diffraction data

Protein powder diffraction is shown to be suitable for obtaining de novo solutions to the phase problem at low resolution via phasing methods such as the isomorphous replacement method. Two heavy-atom derivatives (a gadolinium derivative and a holmium derivative) of the tetragonal form of hen egg-white lysozyme were crystallized at room temperature.

Acta Crystallographica Section D: Biological Crystallography, 2010
 
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Tracking Flavin Conformations in Protein Crystal Structures with

Raman Spectroscopy and QM/MM Calculations

Damaged goods? Detailed knowledge of the cofactor conformation is essential for the functional analysis of flavoenzyme crystal structures. However, photoelectrons generated by X-rays during crystal-data collection can reduce the flavin cofactor and thus change its geometry (see picture). Monitoring of the flavin vibrational modes by Raman spectroscopy during X-ray crystal-data collection provided important information on the actual flavin state.

 

Angewandte Chemie International Edition, 2010
 
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Hydrogen cars coming closer
(http://www.youtube.com/watch?v=3Eo7a7bO8fM
)

 

Superhard Semiconducting Optically Transparent High Pressure Phase of Boron

 

An orthorhombic (space group Pnnm) boron phase was synthesized at pressures above 9 GPa and high temperature, and it was demonstrated to be stable at least up to 30 GPa. The structure, determined by single-crystal x-ray diffraction, consists of B12 icosahedra and B2 dumbbells. The charge density distribution obtained from experimental data and ab initio calculations suggests covalent chemical bonding in this phase.

Phys. Rev. Lett., 2009
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Graphite oxide: Pressure to expand



When pressurized in water, graphite oxide expands

 

Materials that expand when compressed are rare, and are the result of liquid molecules being incorporated into nanoscale pores. The phenomenon has been previously observed in materials such as zeolites, where small unit-cell increases of around 2% have been reported.

Angewandte Chemie International Edition, 2008
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Physico-chemical characterization of the high-silica zeolite catalyst SSZ-74  suggested that it, like the related materials TNU-9  and IM-5 , has a multidimensional 10-ring channel system. Such pore systems are ideal for many petrochemical applications, and indeed SSZ-74 has been shown to be a good catalyst for a wide variety of reactions  Nature Materials, 2008

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An in situ combined high-temperature high-pressure synchrotron radiation diffraction study has been
carried out on LiBH4. The phase diagram of LiBH4 is mapped to 10  GPa and 500  K, and four phases
are identified. The corresponding structural distortions are analyzed in terms of symmetry-breaking
atomic position shifts and anion ordering. Group-theoretical and crystal-chemical considerations reveal
a nontrivial layered structure of LiBH4. The layers and their deformations define the structural stability of the observed phases.
Suggestion.jpg   (Phys. Rev. B, 2008)

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Using high-pressure synchrotron powder diffraction, two new modifications of LiBH4 have been found.
The phase observed at 1.2–10 GPa reveals a novel structural arrangement, where the BH4 group
has an unprecedented square coordination by four Li atoms. The structure exhibits a strikingly
short H···H contact between adjacent BH4 anions, and may show completely different
hydrogen-storage properties if stabilized by chemical substitution at ambient pressure.
(Angew. Chem. Int., 2008)

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Location and disorder of hydrogen atoms in H-rich material, LiBH4, has been established by the scientists of SNBL 
(Yaroslav Filinchuk, Dmirty Chernyshov). This work was awarded a Poster Prize by Oxford Cryosystems at
the 24th European Crystallographic Meeting held in Marrakech in August 2007

 

   



  

 

 

 

 

 

Giant swelling in MOF materials. The reversible "breathing" motion was analyzed in terms of cell dimensions
(extent of breathing), movements within the framework (mechanism of transformation), and the interactions
between the guests and the skeleton. In situ techniques show that these flexible solids are highly selective      absorbents and that this selectivity is strongly dependent on the nature of the organic linker
( Science, 2007 )

  

 

 

Structure solved by enhanced charge. Presentation a charge-flipping structure-solution algorithm,
extended to facilitate the combined use of powder diffraction and electron microscopy data.
( Science, 2007 )

 

 

Complex phenomena in simple metals. A combined in situ high-temperature high-pressure synchrotron
radiation diffraction study has been carried out on In alloys with Cd, Pb, and Sn. The negative thermal
expansion of In and some of the In alloys is a phase-dependent effect resulting from a competition between
spontaneous strain induced by a proper ferroelastic transformation and normal thermal expansion.( Phys.Rev. B, 2007 )

 

 

Raman-Assisted Crystallography. The impact of X-radiation on crystalline taurine has been investigated by time
resolved synchrotron X-ray powder and single crystal diffraction and Raman spectroscopy. Multiple data sets
have been collected at 120 and 296 K.  PCCP, 2007)

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