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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]

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.

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 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.

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 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.

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.

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.

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.

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.

Three different samples of orthorhombic HZSM-5 were analyzed by high-temperature X-ray diffraction and differential scanning calorimetry in order to elucidate the differences in thermal expansion behavior between its hydrated and dehydrated form. The first sample was the as-received orthorhombic HZSM-5, containing three different water species (H 2 O, H 3 O + and OH). The second sample was previously heat treated in a tubular furnace at 550 °C, and, contained only H 2 O, reabsorbed on cooling. The third one was prepared to be completely dehydrated. The dehydrated orthorhombic HZSM-5 sample showed positive thermal expansion from room temperature to 300 °C and negative thermal expansion from 300 °C to 800 °C. On the other hand, the hydrated orthorhombic HZSM-5 exhibited, for the temperature range where water species are present, negative thermal expansion from room temperature to 300 °C (for lattice parameters a and c and volume) and positive thermal expansion from 300 °C to 500 °C. The mechanisms that could explain the thermal expansion behavior of HZSM-5 were discussed.

The isothermal compressibility and bulk thermal expansion of molybdenum diphosphide, MoP2, were measured by in-situ X-ray powder diffraction from ambient conditions to 6.8 GPa and 839 K, respectively. A small anisotropy of the compressibilities in MoP2 appears to be governed by non-bonding interactions in this layer-like material. The thermal expansion data are compared to molybdenum phosphide, MoP, which was measured to 1262 K.

Orthorhombic HZSM-5 zeolite, in hydrated form and with the silica/alumina molar ratio of 30, exhibits a complex thermal expansion behavior over the temperature range 40–840 °C. Strong negative average overall linear coefficient of thermal expansion ( α =−9.0×10 −6 K −1 ) was found in this region. Thermal expansion behavior of HZSM-5 is anisotropic, with the a and c axes contracting more than the b axis. Five different thermal expansion regions could be established over the overall studied temperature range. The first region, between 40 and 80 °C, demonstrated positive average thermal expansion with α =6.19×10 −6 K −1 . The second one, identified between 80 and 440 °C, displays negative average thermal expansion with α =−7.38×10 −6 K −1 . The next region between 440 and 520 °C shows a small positive average thermal expansion with α =3.89×10 −6 K −1 . The fourth region has a strong negative average thermal expansion with α =−6.22×10 −6 K −1 , while the last one exhibits a very strong negative average thermal expansion with α =−25.75×10 −6 K −1 . It could be concluded that the release of H 2 O molecules does not provoke negative average thermal expansion of HZSM-5. One can ascribe the negative thermal expansion behavior of orthorhombic HZSM-5 from 80 to 440 °C mainly to the action of H 3 O + species. The thermal expansion behavior in the range between 440 and 520 °C could be correlated to the processes of dehydroxylation. Above 520 °C the strong negative thermal expansion seems to be related to the intrinsic mechanism of negative thermal expansion, i.e., transverse vibrations of the bridging oxygen atoms between two rigid polyhedrons.

Magnesiumchromite, MgCr2O4, undergoes a structural transition from a cubic spinel structure [space group Fd3m, a=8.32768(4) Å at 16 K] into a tetragonal distorted structure [space group I41/amd, a=5.89199(5) Å, c=8.31677(8) Å at 10 K], isotypic with Hausmannite, Mn3O4. This phase transition is translationengleich and takes place very close or at the antiferromagnetic ordering temperature.

The capability of X-ray diffraction for the microstructure investigations of metastable systems is illustrated on supersaturated and partially decomposed thin films of titanium aluminium nitrides with high aluminium content. The anisotropy of the elastic constants and their role in these investigations is discussed., Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species.

The synthesis of fiber-textured Ti2AlN(0001) films on SiO2 was characterized by in-situ and ex-situ X-ray scattering and Rutherford backscattering spectrometry. Ti2AlN was formed by solid-state reaction between sequentially deposited Ti and AlN layers. A deposition at 275 °C yields a Ti(0001) outof-plane orientation which is maintained for the following AlN(0001)/Ti(0001) layers. Annealing to 600 °C yields AlN decomposition and diffusion of Al and N into Ti, with consecutive transformation into Ti3AlN(111) and Ti2AlN(0001) plus AlN residuals. Despite preferred Ti2AlN(0001) out-ofplane orientation, the in-plane distribution is random, as expected from the self-organized pseudo-epitaxial growth.

Carbon diffusion barriers are introduced as a general and simple method to prevent premature carbon dissolution and thereby to significantly improve graphene formation from the catalytic transformation of solid carbon sources. A thin Al2O3 barrier inserted into an amorphous-C/Ni bilayer stack is demonstrated to enable growth of uniform monolayer graphene at 600 °C with domain sizes exceeding 50 μm, and an average Raman D/G ratio of

Low-temperature (∼450 °C), scalable chemical vapor deposition of predominantly monolayer (74%) graphene films with an average D/G peak ratio of 0.24 and domain sizes in excess of 220 μm2 is demonstrated via the design of alloy catalysts. The admixture of Au to polycrystalline Ni allows a controlled decrease in graphene nucleation density, highlighting the role of step edges. In situ, time-, and depthresolved X-ray photoelectron spectroscopy and X-ray diffraction reveal the role of subsurface C species and allow a coherent model for graphene formation to be devised.

Results of simultaneous thermal analysis, synchrotron and neutron powder diffraction in the range from room temperature up to the melting point at 936 K on non-superionic orthorhombic β-AgCuS as well as on superionic hexagonal α- and cubic δ-AgCuS are reported. On heating the sample is only stable in argon. The following phase transitions occur in AgCuS at elevated temperatures: β 361 K −→ α 399 K −→ α + δ 439 K −→ δ. The volume changes at the superionic β −→ α and α −→ δ phase transitions are about 2.3 and 0.6%. The volume thermal expansion coefficients are 26 × 10−6, 130 × 10−6 and 85 × 10−6 K−1 for the pure β-, α-and δ-phases, respectively. Models forthe average structures of α-and δ-AgCuS are proposed and discussed. Ionic conductivity in δ-AgCuS may originate from cation jumps in ‘skewed’ (100) directions between nearest-neighbour tetrahedral sites via the peripheries of the octahedral cavities. A correlation between the temperature dependence of the cation redistribution in δ-AgCuS and the temperature dependence of the ionic conductivity is assumed. A two-dimensional nature of the ionic conductivity due to cation jumps in slabs perpendicular to the c-direction is supposed for α-AgCuS. There is no evidence for ionic diffusion through the (1/2, 1/2, 1/2) site in (111) directions in either superionic α-or δ-phases.

LiCoPO4 samples were synthesized by two different techniques (high-temperature solid-state reaction and lower-temperature synthesis using NH4CoPO4·H2O as precursor) and tested as cathode materials for 5-V lithium batteries. An irreversible lithium deinsertion was observed for the high-temperature sample. In contrast, the application of lower-temperature synthesis led to a significant improvement of the lithium storage reversibility. Different delithiation mechanisms in LiCoPO4 were found for the samples obtained by different synthetic techniques. The nature of capacity fading during cycling of the cells is discussed.

A.J.Cavaleiro, A.S. Ramos, and M.T. Vieira, CEMUC, Department of Mechanical Engineering, University of Coimbra, Coimbra, Portugal; R.M.S. Martins and F.M. Braz fernandes, CENIMAT I3 N, Materials Science Department, FCT/UNL, Monte de Caparica, Portugal; and C.Baehtz, Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany. Contact e-mails: andre.cavaleiro@dem.uc.pt, sofia.ramos@dem.uc.pt, rmsm@fct.unl.pt, baehtz@esrf.fr, teresa.vieira@dem.uc.pt, and fbf@ fct.unl.pt. JMEPEG (2014) 23:3412 ASM International DOI: 10.1007/s11665-014-1119

Combined in situ X-ray scattering techniques using synchrotron radiation were applied to investigate the crystallization behavior of Sb-rich Ga-Sb alloys. Measurements of the sheet resistance during heating indicated a reduced crystallization temperature with increased Sb content, which was confirmed by in situ X-ray diffraction. The electrical contrast increased with increasing Sb content and the resistivities in both the amorphous and crystalline phases decreased. It was found that by tuning the composition between Ga:Sb = 9:91 (in at.%) and Ga:Sb = 45:55, the change in mass density upon crystallization changes from an increase in mass density which is typical for most phase change materials to a decrease in mass density. At the composition of Ga:Sb = 30:70, no mass density change is observed which should be very beneficial for phase change random access memory (PCRAM) applications where a change in mass density during cycling is assumed to cause void formation and PCRAM device failure.

Electrochemical lithium extraction from LiMn0.6Fe0.4PO4 was revealed to proceed through two two-phase regions in contrast to the mechanism earlier reported. All phases appearing during charging of the cell have the same olivine-like structure with different cell parameters.