Structure and interstitial iodide migration in hybrid perovskite methylammonium lead iodide

Hybrid perovskites form an emerging family of exceptional light harvesting compounds. However, the mechanism underpinning their photovoltaic effect is still far from understood, which is impeded by a lack of clarity on their structures. Here we show that iodide ions in the methylammonium lead iodide migrate via interstitial sites at temperatures above 280 K. This coincides with temperature dependent static distortions resulting in pseudocubic local symmetry. Based on bond distance analysis, the migrating and distorted iodines are at lengths consistent with the formation of I2 molecules, suggesting a 2I→I2+2e redox couple. The actual formula of this compound is thus (CH3NH3)PbI3−2x(I2)x where x0.007 at room temperature. A crucial feature of the tetragonal structure is that the methylammonium ions do not sit centrally in the A-site cavity, but disordered around two off-centre orientations that facilitate the interstitial ion migration via a gate opening mechanism.

Nature Communications 8, 2017





A disorder-enhanced quasi-one-dimensional superconductor

A powerful approach to analysing quantum systems with dimensionality d>1 involves adding a weak coupling to an array of one-dimensional (1D) chains. The resultant quasi-1D (q1D) systems can exhibit long-range order at low temperature, but are heavily influenced by interactions and disorder due to their large anisotropies. Real q1D materials are therefore ideal candidates not only to provoke, test and refine theories of strongly correlated matter, but also to search for unusual emergent electronic phases. Here we report the unprecedented enhancement of a superconducting instability by disorder in single crystals of Na2−δMo6Se6, a q1D superconductor comprising MoSe chains weakly coupled by Na atoms. We argue that disorder-enhanced Coulomb pair-breaking (which usually destroys superconductivity) may be averted due to a screened long-range Coulomb repulsion intrinsic to disordered q1D materials. Our results illustrate the capability of disorder to tune and induce new correlated electron physics in low-dimensional materials.

Nature Communications 7, 2016





Spiral spin-liquid and the emergence of a vortex-like state in MnSc2S4

Spirals and helices are common motifs of long-range order in magnetic solids, and they may also be organized into more complex emergent structures such as magnetic skyrmions and vortices. A new type of spiral state, the spiral spin-liquid, in which spins fluctuate collectively as spirals, has recently been predicted to exist. Here, using neutron scattering techniques, we experimentally prove the existence of a spiral spin-liquid in MnSc2S4 by directly observing the ‘spiral surface’—a continuous surface of spiral propagation vectors in reciprocal space. We elucidate the multi-step ordering behaviour of the spiral spin-liquid, and discover a vortex-like triple-q phase on application of a magnetic field. Our results prove the effectiveness of the J1J2 Hamiltonian on the diamond lattice as a model for the spiral spin-liquid state in MnSc2S4, and also demonstrate a new way to realize a magnetic vortex lattice through frustrated interactions.

Nature Physics, 2016




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



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



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



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


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

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

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



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



Hydrogen cars coming closer


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


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
talyzin copie.jpg


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




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)

highlight_vip_prb copie.jpg



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)




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)