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Journal of synchrotron radiation 28(5), 28 (2021). doi:10.1107/S1600577521007335, The European XFEL delivers up to 27000 intense (>1012 photons) pulses per second, of ultrashort (≤50 fs) and transversely coherent X-ray radiation, at a maximum repetition rate of 4.5 MHz. Its unique X-ray beam parameters enable groundbreaking experiments in matter at extreme conditions at the High Energy Density (HED) scientific instrument. The performance of the HED instrument during its first two years of operation, its scientific remit, as well as ongoing installations towards full operation are presented. Scientific goals of HED include the investigation of extreme states of matter created by intense laser pulses, diamond anvil cells, or pulsed magnets, and ultrafast X-ray methods that allow their diagnosis using self-amplified spontaneous emission between 5 and 25 keV, coupled with X-ray monochromators and optional seeded beam operation. The HED instrument provides two target chambers, X-ray spectrometers for emission and scattering, X-ray detectors, and a timing tool to correct for residual timing jitter between laser and X-ray pulses., Published by Wiley-Blackwell, [S.l.]

Journal of synchrotron radiation 28(3), 688 - 706 (2021). doi:10.1107/S1600577521002551, The high-precision X-ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X-ray Free-Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X-ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X-ray heating and diffraction of Bi under pressure, obtained using 20 fs X-ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC., Published by Wiley-Blackwell, [S.l.]

The journal of physical chemistry letters 12(12), 3246 - 3252 (2021). doi:10.1021/acs.jpclett.1c00150, The ultrafast synthesis of ε-Fe$_3$N$_{1+x}$ in a diamond-anvil cell (DAC) from Feand N$_2$ under pressure was observed using serial exposures of an X-ray free electron laser (XFEL). When the sample at 5 GPa was irradiated by a pulse train separated by 443 ns, the estimated sample temperature at the delay time was above 1400 K, confirmed by in situ transformation of $α$- to $γ$-iron. Ultimately, the Fe and N$_2$ reacted uniformly throughout the beam path to form Fe$_3$N$_{1.33}$, as deduced from its established equation of state (EOS). We thus demonstrate that the activation energy provided by intense X-ray exposures in an XFEL can be coupled with the source time structure to enable exploration of the time-dependence of reactions under high-pressure conditions., Published by ACS, Washington, DC

Other contributors: Markus Hoelzel, Carsten Baehtz, Isabel Sobrados, Jesús Sanz. Sodium hexatitanate Na2Ti6O13 with a tunnel structure has been proposed to be an attractive anode material for lithium ion batteries because of its low insertion voltage, structural stability and good reversibility. In order to obtain a full understanding of the properties of this titanate, a combination of in situ synchrotron X-ray diffraction, neutron diffraction and 7Li MAS solid-state NMR spectroscopy is used in the present work. During the first insertion stage (centered at 1.3 V) lithium is allocated in square planar LiO4 2c (Li1) sites, minimizing electrostatic repulsion with Na ions. During the second lithium uptake (centered at 1.1 V), Li ions pass from 2c to empty 4i (Li2) sites of y/b = 0.5 planes, near Ti3+ cations. Distribution of Li+ and Na+ ions with respect to Ti3+ cations was deduced from Fourier map differences (Rietveld technique) and NMR quantitative analyses in LiNa2Ti6O13 and Li2Na2Ti6O13 samples. 7Li MAS-NMR analysis showed that Li ions occupy three fourfold coordinated sites with reasonable Li+-O-Ti3+ bond distances, while Na cations remain at eightfold coordinated positions near Ti4+ cations as deduced from 23Na MAS-NMR spectroscopy. 7Li MAS-NMR recorded at increasing temperatures suggests that Li ions move along sinusoidal paths to reduce Li-Na electrostatic interactions. Li mobility along the b-axis is favored by partial occupation of interstitial 4i sites (Li3) located at both sides of Na cations in y/b = 0 planes. In lithium inserted samples the most probable - Li1(2c) → Li3(4i) → Li1(2c) - conduction paths were deduced. However, formation of Li pairs at y/b=0 planes (Li2 sites), where Li ions are located near Ti3+ cations, reduce the amount of mobile Li ions that participate in conduction processes. Proximity of lithium to Li and Na ions limits insertion to ca. 2 Li ions per structural formula. [preprint]

Small angle x-ray scattering (SAXS) is a well established technique to detect nanometer scale structures in matter. In a typical setup, this diagnostic uses a detector with a direct line of sight to the scattering target. However, in the harsh environment of high intensity laser interaction, intense secondary radiation and high-energy particles are generated. Such a setup would therefore suffer a significant increase of noise due to this background, which could eventually prevent such measurements. In this paper, we present a novel tool consisting of a mosaic graphite crystal that works as a mirror for the SAXS signal and allows us to position the detector behind appropriate shielding. This paper studies the performance of this mirror both by experiment at the European XFEL (X-Ray Free-Electron Laser Facility) laboratory and by simulations.

Successive crystallization of amorphous Cr-Zr-O thin films, formation of the (Cr,Zr)2O3/(Zr,Cr)O2 nanocomposites and the thermally induced changes in the hexagonal crystal structure of metastable (Cr,Zr)2O3 were investigated by means of in situ high-temperature synchrotron diffraction experiments up to 1100 °C. The thin films were deposited at room temperature by using reactive ion beam sputtering, and contained 3–15 at.% Zr. At low Zr concentrations, chromium-rich (Cr,Zr)2O3 crystallized first, while the crystallization of zirconium-rich (Zr,Cr)O2 was retarded. Increasing amount of zirconium shifted the onset of crystallization in both phases to higher temperatures. For 3 at.% of zirconium in amorphous Cr-Zr-O, (Cr,Zr)2O3 crystallized at 600 °C. At 8 at.% Zr in the films, the crystallization of (Cr,Zr)2O3 started at 700 °C. At 15 at.% Zr, the Cr-Zr-O films remained amorphous up to the annealing temperature of 1000 °C. Metastable hexagonal (Cr,Zr)2O3 accommodated up to ~ 3 at.% Zr. Excess of zirconium formed tetragonal zirconia, which was stabilized by chromium.

In this study we investigated the correlation between microstructure and residual strain relaxation in nanocrystalline Pt films with a thickness of about 20 nm produced by different deposition techniques: magnetron sputtering and ion beam sputtering. X-ray diffractometry was carried out using synchrotron radiation. The out-of-plane interplanar distance was measured during isothermal in situ annealing at temperatures between 130 °C und 210 °C. The thermoelastic expansion coefficient is equal for both types of nanocrystalline Pt films and slightly lower than for coarse grained Pt. The relaxation of residual out-of-plain strain depends on temperature and is significantly stronger in the case of the magnetron sputtered films than for the ion beam sputtered films. Different relaxation of compressive stress is ascribed to the different microstructures which evolve during deposition via the corresponding deposition technique. Thickness fringes around the (1 1 1) Bragg peak deposited via magnetron sputtering reveal that these films are essentially composed of columnar (1 1 1) oriented grains which cover the whole film thickness. In contrast, no thickness fringes are observed around the (1 1 1) Bragg peak of films prepared by ion beam sputtering indicating a significantly different microstructure. This is confirmed by Electron Backscatter Diffraction which reveals a (1 1 1) texture for both types of films. The (1 1 1) texture, however, is significantly stronger in the case of the magnetron sputtered films. Grain growth at low homologous temperatures is considered to be an important contribution to relaxation of residual stress.

Ferromagnetic GaMnP layers were prepared by ion implantation and pulsed laser annealing (PLA). We present a systematic investigation on the evolution of microstructure and magnetic properties depending on the pulsed laser annealing energy. The sample microstructure was analyzed by high-resolution X-ray diffraction (HR-XRD), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), ultraviolet Raman spectroscopy (UV-RS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The presence of X-ray Pendellösung fringes around GaP (004) and RBS channeling prove the epitaxial structure of the GaMnP layer annealed at the optimized laser energy density (0.40 J/cm(2)). However, a forbidden TO vibrational mode of GaP appears and increases with annealing energy, suggesting the formation of defective domains inside the layer. These domains mainly appear in the sample surface region and extend to almost the whole layer with increasing annealing energy. The reduction of the Curie temperature (TC) and of the uniaxial magnetic anisotropy gradually happens when more defects and the domains appear as increasing the annealing energy density. This fact univocally points to the decisive role of the PLA parameters on the resulting magnetic characteristics in the processed layers, which eventually determine the magnetic (or spintronics) figure of merit.

The diffusion bonding of Ti-6Al-4V to NiTi alloys assisted by Ni/Ti reactive multilayer thin films indicates the diffusion of Ni from the filler material towards bulk Ti-6Al-4V. As a consequence, the fragile NiTi2 intermetallic phase is formed at the joint interface. In this context, the aim of this work is to investigate the occurrence of Ni diffusion from Ni/Ti nanomultilayers towards Ti-6Al-4V substrates. For this purpose, multilayer coated Ti alloys were studied in situ at increasing temperatures using synchrotron radiation. After heat treatment, scanning electron microscopy (SEM) analyses were carried out and elemental map distributions were acquired by electron probe microanalysis (EPMA). The EPMA maps confirm the occurrence of Ni diffusion, the presence of Ni in the substrate regions immediately underneath the nanomultilayers is clearly indicated and becomes more pronounced as the temperature increases. The presence of Ni is observed in the same locations where V is found, thus in &beta, Ti grains of Ti-6Al-4V. At the same time, the synchrotron results together with SEM analyses allow the increase of the amount of &beta, Ti phase in Ti-6Al-4V to be identified, while the thin films are mainly constituted by NiTi2. Therefore, the presence of the brittle NiTi2 intermetallic phase can be avoided if Ni diffusion is prevented.

X-ray diffraction using synchrotron radiation was used for real-time investigation of the phase evolution of Ni/Ti multilayer thin films during annealing. These multilayers were deposited onto Ti–6Al–4V substrates by dc magnetron sputtering from pure Ni and Ti targets. The deposition parameters were adjusted in order to obtain a near equiatomic chemical composition and modulation periods (Λ) below 25 nm. Along the entire thickness of the films, well-defined structures with alternate Ni- and Ti-rich layers are observed, even for Λ = 4 nm. In this case, a halo characteristic of an amorphous structure is obtained, while for Λ of 12 and 25 nm the as-deposited thin films are nanocrystalline being possible to identify the (111) Ni and (002) Ti diffraction peaks. The nanolayered structure vanishes during annealing due to interdiffusion followed by reaction. The reaction between Ni and Ti to produce NiTi in the cubic B2 structure occurs in a short delay of time and within a narrow temperature range. For Λ of 25, 12 and 4 nm, the reaction temperature is close to 320, 350 and 385 °C, respectively. For higher temperatures, in addition to the austenitic phase, the NiTi 2 phase is identified. The diffusion of Ti from the substrate and Ni towards the substrate could favour the precipitation of NiTi 2 .

The combination of powerful optical lasers and an x-ray free-electron laser (XFEL) provides unique capabilities to study the transient behavior of matter in extreme conditions. The high energy density science instrument (HED instrument) at the European XFEL will provide the experimental platform on which an unique x-ray source can be combined with various types of high-power optical lasers. In this paper, we highlight selected scientific examples together with the associated x-ray techniques, with particular emphasis on femtosecond (fs)-timescale pump–probe experiments. Subsequently, we present the current design status of the HED instrument, outlining how the experiments could be performed. First user experiments will start at the beginning of 2018, after which various optical lasers will be commissioned and made available to the international scientific community.

Relaxation of stress and point defects in ion-beam-sputtered Pt films with a thickness of 20 and 40 nm during isothermal annealing was investigated. First, isothermal differential dilatometry measurements based on X-ray analysis were carried out between 130 and 400 °C. They show that the relaxation of compressive stress is associated with the formation of vacancies at the surface. From the measurements, an activation enthalpy of 0.14 eV was estimated for the stress relaxation process. In addition, self-diffusion experiments of Pt were carried out on the same type of films using stable 194Pt tracer. From secondary ion mass spectrometry on samples annealed for longer times, an activation enthalpy of 0.5 eV for Pt diffusion in grain boundaries was estimated. The influence of vacancy creation at the surface, vacancy transport, and the annihilation of non-equilibrium bulk interstitials and thermally created vacancies on stress relaxation is discussed.

The isostructural decomposition of the titanium aluminium nitride supersaturated solid solution crystallising in the face centred cubic (fcc) crystal structure into the titanium-rich fcc-(Ti,Al)N and almost titanium-free fcc-(Al,Ti)N and the transformation of metastable fcc-(Ti,Al)N into the wurtzitic aluminium nitride are discussed from the crystallographic point of view by taking the observed orientation relationships between the adjacent phases into account. It is shown that the isostructural decomposition of fcc-(Ti,Al)N into Ti-rich fcc-(Ti,Al)N and fcc-(Al,Ti)N and the transformation of the metastable fcc-(Ti,Al)N into the thermodynamically stable wurtzitic phase are concurrent processes, which are controlled not only by the thermodynamic stability of the respective compound and by the diffusivity of Al and Ti, but also by the local lattice strains. A part of the local lattice strains is regarded to result from the lattice misfit at the interfaces between the titanium aluminium nitrides having different [Al]/[Ti] concentration ratios and, in the case of the fcc/wurtzite-type interface, also having different crystal structures. The phase transition of the fcc-(Ti,Al)N to the wurtzitic one was predicted to be facilitated by stacking faults. The results of crystallographic considerations were verified experimentally by using in situ high-temperature synchrotron diffraction experiments that were performed on cathodic arc evaporated (Ti,Al)N thin films containing titanium and aluminium in different amounts.

The electrochemical properties of TiO2 with the hollandite structure (TiO2(H)) as a negative electrode material for sodium-ion batteries are reported. TiO2(H) was obtained from hollandite K0.21TiO2 by an oxidation–ion extraction process. Na/TiO2(H) cells exhibit a large first discharge capacity of 280 mA h g−1 down to 0.2 V. After the first discharge the Na/TiO2(H) cells develop a reversible charge–discharge capacity of 85 mA h g−1 at C/8 rate in the 2.5–0.2 V voltage range; this corresponds to the reversible insertion of 0.25 Na per TiO2(H) formula unit. Chronoamperometry and potentiostatic intermittent titration techniques were used to further characterize the electrochemical reaction mechanism. Structural changes in the TiO2(H) electrode upon sodium insertion and extraction have been studied by ex situ XRD and high resolution in situ synchrotron diffraction techniques, for which appropriately modified coin-type cells were used. It is seen that sodium insertion into TiO2(H) is commenced with a single-phase solid solution followed by a structural transition from tetragonal I4/m to monoclinic I2/m symmetry, in which the skeleton framework is retained. The reversible transition includes few structural changes with a small volume change of only 1.1%. Fourier difference maps deduced from SXRD patterns revealed the location of Na ions in 4i sites in the tunnel space. The coordination arrangement around Na ions is distorted capped trigonal prisms formed by seven oxygen atoms. Although still far from the theoretical capacity (335 mA h g−1), the cycling properties at a low insertion potential together with the host framework stability indicate the feasibility of TiO2 with the hollandite structure as a negative electrode material for Na-ion batteries.

Complementary in situ X-ray photoelectron spectroscopy (XPS), X-ray diffractometry, and environmental scanning electron microscopy are used to fingerprint the entire graphene chemical vapor deposition process on technologically important polycrystalline Cu catalysts to address the current lack of understanding of the underlying fundamental growth mechanisms and catalyst interactions. Graphene forms directly on metallic Cu during the high-temperature hydrocarbon exposure, whereby an upshift in the binding energies of the corresponding C1s XPS core level signatures is indicative of coupling between the Cu catalyst and the growing graphene. Minor carbon uptake into Cu can under certain conditions manifest itself as carbon precipitation upon cooling. Postgrowth, ambient air exposure even at room temperature decouples the graphene from Cu by (reversible) oxygen intercalation. The importance of these dynamic interactions is discussed for graphene growth, processing, and device integration.

Nickel–Titanium (Ni–Ti) thin film shape memory alloys (SMAs) have been widely projected as novel materials which can be utilized in microdevices. Characterization of their physical properties and its correlation with phase transformations has been a challenging issue. In the present study, X-ray beam diffraction has been utilized to obtain the structural information at different temperatures while cooling. Simultaneously, electrical resistivity (ER) was measured in the phase transformation temperature range. The variation of ER and integral area of the individual diffraction peaks of the different phases as a function of temperature have been compared. A mismatch between the conventional interpretation of ER variation and the results of the XRD data has been clearly identified.

International audience; In order to optimize materials for phase change random access memories (PCRAM), the effect of Ge doping on Ga-Sb alloy crystallization was studied using combined in situ synchrotron x-ray techniques, electrical measurements, and static laser testing. The present data emphasize that the crystallization temperature can be increased up to 390 degrees C with subsequent higher thermal stability of the amorphous phase; phase segregation is evidenced with GaSb, Sb, and Ge phases that crystallize in a two-step crystallization process. The Ge-doped GaSb films exhibit a larger electrical contrast as compared to undoped GaSb alloy (up to x 100). The optical contrast measured by laser testing is shown to follow the mass density change variations upon crystallization, with a negative contrast (higher value in amorphous state) whatever Ge-doping levels. In situ x-ray reflectivity measurements show that zero mass density change can be achieved by low Ge-doping. Ge-doped GaSb alloys look promising since a phase change material with zero mass density change and higher crystallization temperature satisfactorily fulfills the specifications for reliable PCRAM cells in terms of endurance and data retention. (C) 2016 AIP Publishing LLC.

In this work we investigated the structural re-organization of thin nanocrystalline Pt films in the temperature range between 250 °C and 400 °C by in-situ XRD, GIXRD and XRR synchrotron experiments. A re-orientation of (111) atomic planes and a relaxation of residual stress occurs. After heating up, Bragg peak fringes can be observed in the diffractograms. They are a direct proof that the Pt films are built of (111) columnar grains which essentially reach the whole film thickness of about 40 nm. During isothermal annealing a relaxation of the dispersion parameter of the atomic planes takes place which is associated with an activation energy of (0.4 ± 0.1) eV.

The development of a scalable, economical production technique for monoand few-layer graphene (M-/FLG) is a key requirement to exploit its unique properties for applications. Catalytic chemical vapour deposition (CVD) has emerged as one of the most promising and versatile methods for M-/FLG growth. The generic principle of catalytic, rather than pyrolytic, CVD is to expose a catalyst template to a gaseous precursor at temperatures/conditions for which the precursor preferentially dissociates on the catalyst. Hence, the catalyst is key to M-/FLG formation, in particular its role in precursor dissociation, C dissolution, M-/FLG nucleation and domain growth/merging. Although the structure of as-formed graphitic layers on crystalline transition metal surfaces under ultra-high vacuum conditions has been extensively studied in surface science, a central question remains: what M-/FLG quality can be achieved with CVD, in particular, if for cost effectiveness sacrificial polycrystalline metal films/foils and less stringent vacuum/CVD process conditions are used. There have been numerous recent reports of large area M-/FLG CVD on for instance poly-crystalline Ni and Cu, including integrated roll-to-roll processing. However, there is currently very limited understanding of the detailed growth mechanisms, and the mostly empirical process calibrations provide little fundamental insight in to how the process and M-/FLG quality/domain size can be optimised. Herein, we study M-/FLG CVD by complementary in situ probing under realistic process conditions with the aim of revealing the key growth mechanisms. We focus on poly-crystalline Ni films and simple one-step hydrocarbon exposure conditions. However, as highlighted by Figure 1, even for such seemingly simple CVD conditions, the parameter space is manifold which leads to ambiguity in the interpretation of post-growth process characterisation and motivates our in situ approach. For catalyst metals with a high C solubility, such as Ni, current literature typically assumes C precipitation upon cooling as the main growth process. 8] M-/FLG precipitation has been studied in detail for slow, near thermodynamic equilibrium thermal cycling of C doped crystals. 9] For CVD, however, the conditions are distinctly different (Figure 1): an isothermal C precursor exposure phase, which represents a variation in composition rather than temperature, is followed by a typically fast cooling or thermal quenching. Hence kinetic aspects are important. Additionally, competing processes might influence the growth outcome such as etching of M-/FLG in a reactive atmosphere, for example, hydrogen or water, during the CVD process. By combining in situ, timeand depth-resolved X-ray photoelectron spectroscopy (XPS) and in situ X-ray diffraction (XRD), we can clearly show that M-/FLG growth occurs during isothermal hydrocarbon exposure and is not limited to a precipitation process upon cooling. While the fraction of M-/FLG due to isothermal growth and precipitation upon cooling strongly depends on process conditions, we show that the former is dominant for the low-temperature CVD conditions used. We find that M-/FLG nucleation is preceded by an increase in (subsurface) dissolved C with the formation of a solid solution of C in the Ni film, which indicates that graphene CVD is not a purely surface process. We discuss our data here in the context of simple considerations of C solubility and diffusivity as well as rate equations of the basic contributing processes, in order to establish a framework to guide future improvements in graphene CVD by a more fundamental understanding. We perform in situ XPS during low-pressure CVD of M-/FLG from hydrocarbon precursors on Ni(550 nm) films. Figure 2A Figure 1. Illustrative processing profile for a simple one-step hydrocarbon exposure consisting of four major phases: catalyst pretreatment, C dissolution into the catalyst during initial precursor exposure, isothermal M-/FLG growth with continued precursor exposure, M-/FLG growth by precipitation upon cooling. The key catalyst and M-/FLG properties that may be defined at each phase of growth are also listed.

The influence of the microstructure of the as-deposited cathodic arc evaporated Ti 1-x Al x N coatings and, in particular, the influence of the intrinsic lattice strains on their thermal stability were investigated by in-situ synchrotron high temperature glancing angle X-ray diffraction (HT-GAXRD) experiments up to 850 °C. The microstructure of the as-deposited coatings was adjusted by the bias voltage (U B = −40 V, U B = −80 V and U B = −120 V) and by the [Al]/([Ti] + [Al]) ratio (0.4, 0.5 and 0.6) of the used Ti–Al targets. The microstructure evolution during annealing was described in terms of the phase composition of the coatings, the aluminium content, aluminium distribution and residual lattice strains in fcc-(Ti,Al)N. Independent of the deposition parameters ([Al]/([Ti] + [Al]) ratio and bias voltage), all coatings contained a mixture of fcc-(Ti,Al)N, fcc-AlN and w-AlN after annealing at 850 °C. The [Al]/([Ti] + [Al]) ratio was found to control the amount of fcc-(Ti,Al)N, whereas the bias voltage was mainly responsible for the relative amount of fcc-AlN and w-AlN. Finally, the interplay between lattice strains and the kinetics of the spinodal decomposition of fcc-(Ti,Al)N was illustrated.

Three magnesium-based alloys, Mg 90 Ni 10 , Mg 80 Ni 10 Y 10 and Mg 85 Cu 5 Ni 5 Y 5 , were prepared by melt-spinning and compared regarding their hydrogen desorption properties. Their hydrogen desorption kinetics after activation and hydrogenation was investigated by thermogravimetry at different temperatures in the range from 150 °C to 250 °C. It was found that Mg 80 Ni 10 Y 10 exhibits a much faster desorption kinetics in comparison to Mg 90 Ni 10 and Mg 85 Cu 5 Ni 5 Y 5 of up to 1.3 wt.%-H 2 /min. The corresponding crystal phase transformations were investigated in detail by in situ synchrotron X-ray diffraction. It was found that the kinetics of hydrogenation is controlled by different reaction pathways for Mg 90 Ni 10 , Mg 80 Ni 10 Y 10 and Mg 85 Cu 5 Ni 5 Y 5 .

Actuation frequencies in thermally triggered Shape Memory Alloy (SMA) thin films are limited by the slow heat transport into/out of the films. Carbon Nanotubes (CNTs) are known to exhibit an exceptionally high thermal conductivity. Thus, we propose to thermally contact SMA films with CNTs to increase SMA actuation frequencies by enhanced heat transport through the CNTs. The basic requirement for this envisaged nanotube application is to obtain CNT forest growth on a SMA material while retaining a reversible martensitic transformation, as required for Shape Memory Effect exploitation. We show how such growth can be achieved on thin films of the SMA material NiTi. Future work is needed to measure thermal properties and obtainable cycling frequencies of CNT-SMA structures.

The thermodynamics of structural phase transformations in thin films depends on the mechanical stress that can be released by plastic deformation. For thin films below a critical film thickness, plastic deformation is energetically unfavourable: thus, the system stays coherent and stress remains. For PdHc films less than 22 nm thick, a new situation emerges: while the interfaces between matrix and hydride precipitates remain coherent throughout the complete phase transition, misfit dislocations form between the hydride phase and the substrate.

Electrodes consisting of composites of nanosized-LaPO4/Carbon-Super P yield irreversible capacities as large as 872 mAh/g carbon (down to 0.2 V), which would be equivalent to the reaction of 0.9 lithium ions with LaPO4. Increasing the crystallite size of LaPO4 drastically decreases the specific capacity delivered by the cell, reaching a minimum value of 330 mAh/g carbon for micrometer-LaPO4. A significant capacity is also detected in nanosized LaPO4 /Carbon-KS6 and LaPO4/Ni electrodes. An in situ XRD investigation proves that the bulk of LaPO4 does not react with lithium, evidencing that LaPO4 is useless as electrode material for lithium cells. The reactivity of the electrode is likely due to the electrolyte decomposition on the surface of both the electronic conductor additives (C or Ni) and the LaPO4 nanoparticles.

Two nanocrystalline magnesium-rich alloys, Mg 90 Ni 10 and Mg 80 Ni 10 Y 10 , were produced by melt-spinning. After hydrogenation they consist of a MgH 2 matrix with finely dispersed Mg 2 NiH 4 grains of about 2 μm in size. In the case of Mg 80 Ni 10 Y 10 , nanocrystalline YH 3 grains are found, additionally. The desorption kinetics of hydrogenated Mg 90 Ni 10 and Mg 80 Ni 10 Y 10 was investigated by thermogravimetry at different temperatures in the range from 150 °C to 250 °C. It was observed that Mg 80 Ni 10 Y 10 exhibits a much faster desorption kinetics in comparison to Mg 90 Ni 10 of up to 1.3 wt.% H 2 /min. Differential scanning calorimetry indicates that these alloys undergo a two-step desorption process. The corresponding phase transformations were investigated in detail by in situ synchrotron X-ray diffraction, thus, the different hydrogen desorption kinetics can be explained.

A 3 V cathode material for lithium ion batteries, Li 0.33 MnO 2 , was synthesized by solid-state reaction. Two Mn crystallographic positions, Mn (1) and Mn (2) , were determined by X-ray diffraction analysis. The [Mn (2) O 6 ] octahedron had a lower symmetrical degree than that of [Mn (1) O 6 ], which was attributed to the geometrical effects of the non-symmetrical environment around Mn (2) . Li 0.33 MnO 2 delivered a reversible discharge capacity ∼140 mA h g −1 . In situ synchrotron diffraction clearly showed a reversible phase transition of Li 0.33 MnO 2 during electrochemical process. The analysis of X-ray absorption near edge spectroscopy observed the conversion of Mn 4+ to Mn 3+ with Li + intercalation into Li 0.33 MnO 2 , accompanied by the formation of more severely distorted [MnO 6 ] octahedron.

In situ synchrotron diffraction experiments were performed to study the behaviour of the cathode material LiNi0.8Co0.2O2 at high cycle numbers. The battery-cell was cycled 140 times between 4.2 and 2.7 V. The initial cycle and several cycles at proceeded degradation of the cell were investigated. In between the cell was cycled ex situ. The evolution of the lattice parameters during cycling was determined for the different stages of degradation by means of Rietveld refinement. Comparing the initial cycle of the cell with the higher cycle numbers, the mechanism of lithium insertion/extraction does not change significantly. But, the range in which the lattice parameters change during one cycle becomes smaller. This can be attributed to interface layer formation and to slightly less lithium exchange in the same voltage window.

Single phase spinel solid solutions of LixMn3-x-yFeyO4 series with range of 0.5≤x≤1.0 and 0.2≤y≤1.0, have been synthesized by a solid state reaction. By refining the high-resolution X-ray diffraction patterns with Rietveld profile analysis, the lattice parame- ters, interatomic distances and cation distribution were determined. The Fe-for-Mn substitu- tion increases the spinel unit cell constant from a = 8.27A to a = 8.38A, for the Fe/(Fe+Mn) mole ratio of 0.1 and 0.472, respectively. Evidence is given that the lithium ions occupy the tetrahedral sites exclusively, for the molar ratio 0� Fe/(Mn+Fe) � 0.3.

X-ray powder diffraction was employed to reveal the structural changes occurring upon annealing of quenched, hexagonal Ni1.50Sn below its equilibrium ordering temperature, leading finally to long-range ordered, orthorhombic Ni1.50Sn. The changes in the diffraction patterns indicate that the features of the low-temperature phase develop gradually in two main stages. Ex situ and in situ time-resolved X-ray powder diffraction analysis of the first stage was employed to monitor at various temperatures the time dependence of the lattice axial ratio c/a associated with the formation of long-range order in small domains. Data evaluation using an ‘equivalence-time’ method gave a value of 165–170 kJ/mol for the activation energy of the ordering, indicative of lattice-site changes of Ni atoms.

Neutron powder diffraction studies of Na{sub 1/2}La{sub 1/2}TiO{sub 3} and Na{sub 1/2}Tb{sub 1/2}TiO{sub 3}, and a synchrotron X-ray powder diffraction study of Na{sub 1/2}Eu{sub 1/2}TiO{sub 3} have been carried out. Rietveld refinement of the structures confirmed that Na{sub 1/2}Eu{sub 1/2}TiO{sub 3} and Na{sub 1/2}Tb{sub 1/2}TiO{sub 3} crystallizes in GdFeO{sub 3} type of structure (space group Pbnm). The ambiguity in the literature regarding the crystal structure of Na{sub 1/2}La{sub 1/2}TiO{sub 3} has been resolved and the correct space group is found to be R3-bar c. A detailed list of refined structural parameters of these compounds is presented for the first time.

The morphology of micrometer-sized beta-hematin crystals (synthetic malaria pigment) was determined by TEM images and diffraction, and by grazing incidence synchrotron X-ray diffraction at the air-water interface. The needle-like crystals are bounded by sharp {100} and {010} side faces, and capped by {011} and, to a lesser extent, by {001} end faces, in agreement with hemozoin (malaria pigment) crystals. The beta-hematin crystals grown in the presence of 10% chloroquine or quinine took appreciably longer to precipitate and tended to be symmetrically tapered toward both ends of the needle, due to stereoselective additive binding to {001} or {011} ledges. Evidence, but marginal, is presented that additives reduce crystal mosaic domain size along the needle axis, based on X-ray powder diffraction data. Coherent grazing exit X-ray diffraction suggests that the mosaic domains are smaller and less structurally stable than in pure crystals. IR-ATR and Raman spectra indicate molecular based differences due to a modification of surface and bulk propionic acid groups, following additive binding and a molecular rearrangement in the environment of the bulk sites poisoned by occluded quinoline. These results provided incentive to examine computationally whether hemozoin may be a target of antimalarial drugs diethylamino-alkoxyxanthones and artemisinin. A variation in activity of the former as a function of the alkoxy chain length is correlated with computed binding energy to {001} and {011} faces of beta-hematin. A model is proposed for artemisinin activity involving hemozoin nucleation inhibition via artemisinin-beta-hematin adducts bound to the principal crystal faces. Regarding nucleation of hemozoin inside the digestive vacuole of the malaria parasite, nucleation via the vacuole's membranous surface is proposed, based on a reported hemozoin alignment. As a test, a dibehenoyl-phosphatidylcholine monolayer transferred onto OTS-Si wafer nucleated far more beta-hematin crystals, albeit randomly oriented, than a reference OTS-Si.

The influence of rapid quenching on the phase formation of Cu–Si alloys was investigated for silicon contents between 10 and 30 at.%. Rapid quenching leads to formation of different meta-stable states depending on the chemical composition. High temperature phases η, δ and κ can be preserved at room temperature. The formation of the room temperature phase ɛ can be suppressed by rapid quenching from the melt. The crystal structure of the high temperature phases was analysed by X-ray powder diffraction. Annealing of the rapidly quenched alloys at T = 500 °C leads to the transformations of the meta-stable phases. The equilibrium states exhibit phase compositions, which are in agreement with the generally accepted phase diagram.

HT-LiMnO2 was prepared by a solid-state reaction at 900 °C. Electrochemical charge–discharge cycling of HT-LiMnO2 showed an initial charge capacity 113 mA h g− 1, followed by a small first discharge of 25 mA h g− 1. The discharge capacity subsequently increased and reached up to ∼ 120 mA h g− 1 after 30 cycles. In situ synchrotron diffraction showed that HT-LiMnO2 transformed to a new phase (Phase II) during the first charge process, which was metastable and could easily convert to spinel LiMn2O4 in the following cycles. The progressive formation of this spinel phase was responsible for the capacity increase of the battery in the first cycles. The different cycling performance of HT-LiMnO2 and LT-LiMnO2 was attributed to the large stacking faults in LT-LiMnO2, which may facilitate the material to completely convert to spinel LiMn2O4 in the first charge without the medium transition to Phase II.

In situ synchrotron diffraction revealed a stepwise appearance of two new phases upon electrochemical lithium extraction from LiCoPO4. These phases were demonstrated to have the same olivine-like structure as the pristine compound. The lithium-deficient phases were proposed to be Li0.7CoPO4 and CoPO4. The completely delithiated phase appears to be unstable in air and undergoes amorphization. The phase transitions are reversible, but a slow kinetics of the initial delithiation was identified by in situ synchrotron diffraction and the potentiostatic intermittent titration technique. We demonstrated that the electrochemical extraction of lithium is accompanied by significant electrolyte decomposition, contributing to the capacity loss upon cycling. The galvanostatic intermittent titration technique combined with impedance spectroscopy revealed self-discharge of the cell in the charged state. This study argues different mechanisms of lithium extraction from LiCoPO4 in comparison with LiFePO4 and LiMnPO4.

The scalable chemical vapor deposition of monolayer hexagonal boron nitride (h-BN) single crystals, with lateral dimensions of ∼0.3 mm, and of continuous h-BN monolayer films with large domain sizes (>25 μm) is demonstrated via an admixture of Si to Fe catalyst films. A simple thin-film Fe/SiO2/Si catalyst system is used to show that controlled Si diffusion into the Fe catalyst allows exclusive nucleation of monolayer h-BN with very low nucleation densities upon exposure to undiluted borazine. Our systematic in situ and ex situ characterization of this catalyst system establishes a basis for further rational catalyst design for compound 2D materials.

Pd films can be used as a model system to examine the influence of microstructure and stress on the hydrogen absorption. In this work we study 500 nm Pd films deposited on different substrates with different binding strengths. The films were electrochemically loaded with hydrogen up to hydride concentration. Development of lattice constant during hydrogen loading of Pd films was investigated by in situ X-ray diffraction using synchrotron radiation. The influence of microstructure and mechanical stress in the films on the phase transition from Pd to Pd hydride was examined.

The fabrication of regularly ordered Ge quantum dot arrays on Si surfaces usually requires extensive preparation processing, ensuring clean and atomically ordered substrates, while the ordering parameters are quite limited by the surface properties of the substrate. Here, we demonstrate a simple method for fabrication of ordered Ge quantum dots with highly tunable ordering parameters on rippled Si surfaces. The ordering is achieved by magnetron sputter deposition, followed by an annealing in high vacuum. We show that the type of ordering and lattice vector parameters of the formed Ge quantum dot lattice are determined by the crystallographic properties of the ripples, i.e., by their shape and orientation. Moreover, the ordering is achieved regardless the initial amorphisation of the ripples surface and the presence of a thin oxide layer.

International audience; A quantitative analysis of in situ and operando X‐ray diffraction studies allows for deeper insight into the mechanism of Li2S formation and consumption. A two‐step reaction process is proposed for both discharge and charge. Changing selectivity for Li2S formation is estimated, with solely Li2S being formed during the earliest step, followed by possible concurrent formation of Li2S2 intermediate in the further step of discharge.

As-prepared and annealed (up to 3 days at 633 K and 673 K) e-Fe3N1.0 powders were studied by powder diffraction using synchrotron radiation and transmission electron microscopy. The data reveal the formation of γ'-Fe4N in few powder particles and enrichment of the remaining e-phase with N indicating inter-particle N transfer. Structural diffractionline broadening due to local composition fluctuations was identified in the X-ray line profiles by fitting applying a convolution procedure.

Investigations of the structure transformations of lithium deficient Li 0.95 Mn 2.05 O 4 , in the temperature range of 10–1173 K, have been undertaken with X-ray powder diffraction, using synchrotron radiation, at the HASYLAB high-resolution diffractometer (beamline B2). Single phase spinel-like oxide was obtained by a solid state reaction between α-Mn 2 O 3 and Li 2 CO 3 at 1073 K, followed by rapid quenching of the sample in the solid CO 2 . At the room temperature, the lithium deficient sample (with x = 0.95 in Li x Mn 3− x O 4 ) shows a tetragonally distorted spinel lattice, with c / a = 0.98. No phase transition has been observed when temperature decreased and the sample remained tetragonal in the range 300–10 K. A reversible phase transition appears, however, during very mild heating of Li 0.95 Mn 2.05 O 4 above the room temperature. The tetragonal spinel structure ( F 4 1 / ddm ) undergoes a transition into cubic form ( Fd 3 m ) at 393 K. A thermal treatment above 573 K causes a partial decomposition of the sample, resulting in a formation of a nearly stoichiometric LiMn 2 O 4 , with the admixture of manganese oxides.

The electrochemical performance of LiCoPO4-based electrodes was studied in dependence on synthetic conditions. The role of particle size distribution is illustrated. Structural changes occurring at lithium extraction–insertion were explored by ex situ and in situ synchrotron XRD measurements. For the samples annealed at temperature lower than 600 °C the amorphisation of the cathode material was identified. For a high-temperature sample the two-phase character of electrochemical reaction was confirmed. The character of structural changes observed at charge and discharge is different: the two-phase reaction LiCoPO4–“CoPO4” occurs during charging, while discharge induces a strong increase of the cell volume for the Li-poor phase.

An electrochemical in-situ cell for diffraction studies of battery materials has been developed. The cell works in transmission geometry with sample rotation, and the performance was characterized by experiments on the cathode material LiMn2O4. Several charge and discharge cycles can be studied over a few days without any misfunction of the cell. The quality of the obtained data allows for full structure refinements by the Rietveld method. The whole set-up is about 1 mm thin and consists of an aluminum piston as cathode current collector with a thickness below 0.1 mm in direct contact with a pellet of active cathode material, carbon black and binder. The lithium anode is separated from the cathode by a glass-fibre, soaked with electrolyte. The very good time and angular resolution of this set-up reveals three distinct spinel phases for different charging states of LiMn2O4, prepared by subsolidus reaction.

The influence of the annealing temperature on the degree of cation-disordering in the layered structures was examined for three different compositions of LiNiyCo1-yO2 (y = 0.2, 0.66 and 0.75, respectively). A minimum in cation-disorder is found for annealing temperatures between 700 and 800 °C for y = 0.75, between 750 and 810 °C for y = 0.66 and a less pronounced minimum between 795 and 870 °C for y = 0.2. One optimum annealed sample with y = 0.75 was used for an in situ characterisation using synchrotron radiation. The obtained structural data correlate well with the electrochemical data. The known phase transition occurring during the first cycle was closely observed by ADXRD (angular dispersive X-ray diffraction). The two states of the material during the first cycle could be distinguished and the obtained data were processed by Rietveld refinement.

From pure powders of forms I and II of phenobarbital, X-ray diffraction patterns were recorded at room temperature. The starting crystal structural models were found by a Monte-Carlo simulated annealing method. The structures of the two forms were obtained through Rietveld refinements. Soft restraints were applied on bond lengths and bond angles, all H-atom positions were calculated. The cell of form I is monoclinic with the space group P21/n, Z = 12, Z′ = 3. Form II has a triclinic cell, with the space group P\bar 1, Z = 6, Z′ = 3. For both forms, the crystal cohesion is achieved by networks of N—H...O hydrogen bonds along [101]. The broadening of the Bragg peak profiles is interpreted in terms of isotropic strain effects and anisotropic size effects.