Synchrotron Diffraction Studies Research Articles

Heterogeneity in Li-S Batteries Resolved through Operando Synchrotron Diffraction Studies

Lithium-Sulfur (Li-S) batteries are promising candidates for electric vehicle applications due to their very high theoretical specific capacity (1670 mAh/g) and the tremendous availability and low cost of elemental sulfur. However, their practical capacity is substantially smaller (~1000 mAh/g) and their cycling performance is hindered by numerous technical challenges caused by issues on both cathode and anode sides of the system. While Li-S cells with extended cycling lifetimes can be built, they are typically only effective when using excess electrolytes and applied pressure, limiting their utility for practical applications. To gain deeper insights into the origin of missing capacity and the capacity fade of Li-S cells, we conducted operando studies on Li-S pouch cell batteries using synchrotron powder diffraction techniques. This approach enabled us to sensitively track the various crystalline phases involved in the cycling of Li-S batteries and to resolve a variety of inhomogeneities within cells that may affect their performance and lifetime.

Hypervalent hydridosilicate in the Na-Si-H system.

Hydrogenation reactions at gigapascal pressures can yield hydrogen-rich materials with properties relating to superconductivity, ion conductivity, and hydrogen storage. Here, we investigated the ternary Na-Si-H system by computational structure prediction and in situ synchrotron diffraction studies of reaction mixtures NaH-Si-H2 at 5-10GPa. Structure prediction indicated the existence of various hypervalent hydridosilicate phases with compositions NamSiH(4+m) (m = 1-3) at comparatively low pressures, 0-20GPa. These ternary Na-Si-H phases share, as a common structural feature, octahedral SiH6 2- complexes which are condensed into chains for m = 1 and occur as isolated species for m = 2, 3. In situ studies demonstrated the formation of the double salt Na3[SiH6]H (Na3SiH7, m = 3) containing both octahedral SiH6 2- moieties and hydridic H-. Upon formation at elevated temperatures (>500°C), Na3SiH7 attains a tetragonal structure (P4/mbm, Z = 2) which, during cooling, transforms to an orthorhombic polymorph (Pbam, Z = 4). Upon decompression, Pbam-Na3SiH7 was retained to approx. 4.5GPa, below which a further transition into a yet unknown polymorph occurred. Na3SiH7 is a new representative of yet elusive hydridosilicate compounds. Its double salt nature and polymorphism are strongly reminiscent of fluorosilicates and germanates.

Magneto-electronic coupling to the anomalous lattice expansion in Bi1.8Sb0.2Te[formula omitted] crystal

Our low-temperature synchrotron diffraction studies reveal an anomalous thermal expansion below ∼ 25 K (Tm). Below Tm, the Shubnikov-de Haas (SdH) oscillations are evident and anisotropic with respect to magnetic field, suggesting an anisotropic Fermi surface. Thermal variation of magnetization result shows a minimum around Tm, pointing to a significant magnetoelastic coupling. Paramagnetic singularities in the magnetization curve indicate the robust topologically-protected surface state. Careful comparison of the resistivity and magnetization results link the elastic coupling to the magnetic and electronic structure in Bi1.8Sb0.2Te3, which has not been explored in the well-studied pristine compound Bi2Te3.

C-S-H seeding activation of Portland and Belite cements: An enlightening in situ synchrotron powder diffraction study

C-S-H seeding in Portland cements is well known from basic scientific works and field applications. Moreover, this activation approach could be beneficial for low-CO2 cements under development where a general drawback is poor mechanical strengths during the first week of hydration. However, a mechanistic understanding of the different processes taking place when seeding is still not developed. Here, we contribute to this knowledge gap by studying one commercial Portland cement and two industrial-trial belite cements. Three different admixtures are employed, viz. two types of commercial C-S-H seeding and triisopropanolamine as a typical alkanolamine. A multitechnique approach is employed including calorimetry, ultrasonic pulse velocity, thermal analysis and Rietveld analysis of laboratory X-ray powder diffraction data. Chiefly, an in situ X-ray synchrotron diffraction study has allowed mapping out the evolution of every crystalline phase. Furthermore, the use of an internal standard permitted to measure the changes in the overall amorphous content. In a nutshell, alite and belite (phases) hydrations are not significantly accelerated by C-S-H seeding for the three studied cements. Conversely, sulphate and aluminate phase dissolutions are enhanced. Faster ettringite crystallisation contributes to the observed improved mechanical properties at early ages. Moreover, a synergistic effect between C-S-H seeding and alkanolamine addition is proved. The importance of these findings for the possible acceleration of low-CO2 cement hydration is discussed.

Structural distortion driven enhancement of exchange bias effect in Cu1−xCoxCr2O4

We investigate exchange bias (EB) effect in two members with x = 0.4 and 0.6 of multiferroic Cu1−xCoxCr2O4 series, which are close to the interface between two structures at room temperature and represent with structures having I41/amd and Fd3¯m space groups, respectively. Both the compounds exhibit EB effect having EB field (HE) of 244 and 870 Oe at 2 K for x = 0.4 and 0.6, respectively with a cooling field of 10 kOe, which decrease with increasing temperature and disappear near their ferrimagnetic ordering temperatures (TN) close to 100 K. We note that higher HE correlates the higher coercivity (HC), which is found highest for x = 0.6 in the entire series of compounds. Our low temperature synchrotron diffraction studies for x = 0.6 confirm magnetoelastic as well as electroelastic coupling observed close to TN and ferroelectric ordering temperature (TFE). A structural transition to a polar Ima2 structure from I41/amd is observed close to 154 K, which coincides with TFE. Below TFE, thermal variation of structural distortion defined by (a − b)/(a + b) demonstrates significant magnetoelastic coupling. More importantly, the distortion parameter is found significantly higher than the rest member of the series and provides a hint for the highest corecivity in the entire series and correlates the higher EB effect. Current study demonstrates a correlation between structural distortion and EB effect and provides a clue of improving EB effect through the crystal structural engineering.

In-situ synchrotron diffraction study on compressive deformation behavior of Mg92Y5Ni3 alloy mostly composed of LPSO

The compressive deformation behavior of the as-cast and as-extruded Mg92Y5Ni3 (at.%) alloy mostly composed of long period stacking ordered (LPSO) phase was studied by in-situ synchrotron radiation combined with the analysis of deformation traces after compression at different applied stress. The as-cast alloy has random texture, while the as-extruded alloy has a typical basal texture with basal plane parallel to extrusion (compression) direction. Prior to macro-yielding, some softly oriented grains are preferentially plastically deformed, leading to micro-yielding. The micro-yielding behavior of both as-cast and as-extruded alloys is controlled by basal slip, the as-extruded alloy has higher micro-yielding strength than the as-cast alloy. The activated deformation mode near the macro-yielding point is prismatic slip in both as-cast and as-extruded alloys, and as the hard oriented grains dominate in the as-extruded alloy, the compressive yield strength of the alloy is increased from 217 MPa to 535 MPa after extrusion. The kinking activated following the prismatic slip can introduce a large number of dislocations in the as-extruded alloy, resulting in high strain-hardening rate of 3000 MPa, high ultimate compressive strength of ∼800 MPa and plastic strains above 10%.

Phase-selective degree of hydration at setting: An in situ synchrotron diffraction study

Setting of Portland cements is still not well understood. Previous studies used techniques that analyse the pastes as a whole to correlate setting times with degree of hydration. Here, in-situ synchrotron X-ray diffraction analysed by the Rietveld method, with internal standard methodology, is used to derive alite dissolution rate and the crystallization kinetics of ettringite and portlandite in three commercial cements. Moreover, C–S–H gel precipitation pace has also been determined. C–S–H gel precipitation is key to account for setting. For grey Portland cements with w/c = 0.5, initial setting is attained when alite degree of hydration is close to 20% and the C−S−H gel content reached approximately 6 vol%.

Bulk Rashba Spin Splitting and Dirac Surface State in p‐Type (Bi0.9Sb0.1)2Se3 Single Crystal

Herein, bulk Rashba spin splitting (RSS) and associated Dirac surface state in (Bi0.9Sb0.1)2Se3, exhibiting dominant p‐type conductivity is reported. It is argued that the synchrotron diffraction studies that origin of the bulk RSS is due to a structural transition to a non‐centrosymmetric phase below ≈30 K. The Shubnikov–de Haas–Van oscillations are observed in the magnetoresistance curves at low temperature. The extrapolation of the linear plots for both the and component in the Landau level fan diagram meet at n = 0.40(6) for 1/H = 0, which is close to n = 0.5 is recommended for the Dirac particles. The magnetization results at low temperature exhibit substantial orbital magnetization consistent with the bulk RSS. The bulk RSS and Dirac surface states are confirmed by the first‐principles density functional theory calculations. The coexistence of orbital magnetism, bulk RSS, and Dirac surface state is unique for p‐type (Bi0.9Sb0.1)2Se3, making it an ideal candidate for spintronic applications.

High-Temperature Synthesis and Dielectric Properties of LaTaON2.

The development of new synthetic methodologies of perovskite oxynitrides is challenging but necessary for the search of new compounds and the investigation of new properties. Here, we report a new method of preparation of the perovskite LaTaON2 that has been investigated as a pigment and photocatalyst for water splitting. The synthesis proceeds through the solid-state reactions under N2 at 1500 °C between La2O3, LaN, and Ta3N5 or between LaN and TaON, which are completed after 3 h and lead to sintered, highly crystalline samples with particle sizes up to 1 μm. Nitrogen-deficient samples LaTaO1+xN2-x with x ≤ 0.35 are prepared by changing the N/O ratio in the mixture of reactants. Electron diffraction, synchrotron diffraction, and neutron diffraction studies on stoichiometric and nitrogen-deficient compounds indicate that they crystallize in the monoclinic space group I2/m with lattice parameters for LaTaON2 of a = 5.71458(7), b = 8.05987(10), c = 5.74772(6) Å, and β = 89.982(3)°. The three anion sites of the I2/m structure are partially occupied by oxygen and nitrogen, with a preference of nitride for two positions with occupancies of 77 and 88%. This anion distribution is different from that reported in previous studies of samples prepared by ammonolysis at lower temperature, suggesting that the synthesis conditions affect the anion order of this perovskite. Optical measurements indicate a band gap of about 1.9 eV, which is close to that observed in samples prepared by other methods. The determined dielectric permittivity for LaTaON2 εr ≈ 200, reported for the first time for a highly nitrided pseudocubic perovskite, is similar to that observed in perovskites with one nitrogen per formula.

Salt effects on Li-ion exchange kinetics and activation energies – systematic in situ synchrotron diffraction studies

Salt effects on Li-ion exchange kinetics and activation energies – systematic <i>in situ</i> synchrotron diffraction studies

Unraveling the valence state and phase transformation of iron-based electrocatalysts towards oxygen reduction reaction

The commercialization of fuel cells relies largely upon the development of highly active non-precious metal electrocatalysts. Insufficient understanding of the reaction mechanism of Fe-based electrocatalysts towards oxygen reduction reaction (ORR) limits the further improving of its catalytic performance. Herein the valence state and phase transformation of three Fe-based electrocatalysts comprising different valences of iron during the ORR in alkaline medium are investigated by in situ synchrotron radiation X-ray absorption and diffraction studies in direct borohydride fuel cell. There is a dynamic structure associated with the ‘Fe2+/3+’ redox transition confirmed by in situ X-ray absorption near edge structure spectra in Fe-PPy-C and FeS-PPy-C. The metallic Fe, FeS, and Fe2O3 of the three Fe-based electrocatalysts are all converted to FeOOH during ORR. The local structure of Fe atoms and valence transition barrier contribute to most of the ORR activities of the three Fe-based electrocatalysts.

An in-situ synchrotron diffraction study of stress relaxation in titanium: Effect of temperature and oxygen on cold dwell fatigue

There is a long-standing technological problem in which a stress dwell during cyclic loading at room temperature in Ti causes a drastic fatigue life reduction. To better understand the material characteristics that control or exacerbate this behaviour, evaluation of the time dependent plasticity of the main prismatic and basal slip systems is critical. Incorporating the influence of operating temperatures and common alloying elements on cold dwell fatigue will be beneficial for future alloy design to address this problem. In this work, characterisation of the time dependent plastic behaviour of two commercially pure titanium samples (grade 1 and grade 4) with different oxygen content at 4 different temperatures (room temperature, 75 °C, 145 °C and 250 °C) was performed during stress relaxation using synchrotron X-ray diffraction. Key parameters that govern the dislocation motion were determined for the major prismatic and basal slip systems as a function of temperature and oxygen content by calibrating a crystal plasticity finite element model with the measured lattice strain relaxation responses. From the temperatures assessed, 75 °C was found to be the worst-case scenario, where the macroscopic plastic strain accumulation was significant during a relaxation cycle due to the greatest activity of both prism and basal slip systems. As the temperature increases, the contribution of thermal energy becomes greater than mechanical energy for dislocation glide. Oxygen was found to have a stronger strengthening effect on prism slip over basal slip, through a significant change in their respective critical resolved shear stresses. This effect becomes more significant in high oxygen content commercially pure Ti.

In situ synchrotron diffraction study of a crack-free additively manufactured Ni base superalloy

The tensile deformation behaviour of a crack-free additively manufactured (AM) Ni base superalloy and its wrought (W) counterpart has been investigated by in-situ synchrotron X-ray diffraction. In order to understand the evolution of dislocation character, dislocation density (ρ), coherent scattering domain size (D) and dislocation arrangement parameter (M), the diffraction data corresponding to the first six{hkl} reflections have been analyzed using modified Williamson-Hall and modified Warren-Averbach methodologies. The ρ was found to be relatively higher in AM superalloy as compared to W superalloy during both the regimes of elastic and plastic deformation. In the plastic deformation regime, while the fraction of edge and screw dislocations was found to be nearly equal in proportion in W superalloy, the fraction of screw dislocations remained higher in AM superalloy. In view of the relatively high initial ρ and inefficacy of D in AM superalloy, heat treatment in as-built parts is suggested.

Rhombohedral distortion-driven ferroelectric order and exchange bias effect in geometrically frustrated ZnFe2O4

The rhombohedral distortion-driven occurrence of the spontaneous electric polarization at a reasonably high temperature $(T)$ and an exchange bias (EB) effect below the antiferromagnetic (AFM) N\'eel temperature $({T}_{N})$ are revealed in ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$. We observe the magnetic memory effect, suggesting a cooperative glassy magnetic state below ${T}_{N}$. The phase separation between the long-range AFM and the glassy magnetic component leads to the EB effect below ${T}_{N}$. The synchrotron diffraction studies confirm a structural transition to a polar $R3m$ structure from the cubic spinel structure, involving a strong rhombohedral distortion. This distortion correlates with the occurrence of the spontaneous electric polarization $(P)$ below $\ensuremath{\sim}110$ K $({T}_{\text{FE}1})$, which is accompanied by a short-range order (SRO). The $P$-value enhances further due to an additional rhombohedral distortion below ${T}_{N}$. A considerable magnetoelectric (ME) coupling is detected below ${T}_{\text{FE}1}$. The increase of $P$ is $\ensuremath{\sim}7.2$% for 5 T at the liquid nitrogen temperature. There has been a fundamental interest among the community in the unique result of the occurrence of ferroelectric (FE) order coexisting with SRO and having a significant ME coupling, which is accompanied by a strong rhombohedral structural distortion analogous to that observed in ${\mathrm{BiFeO}}_{3}$.

In-situ synchrotron diffraction study of the localized phase transformation and deformation behavior in NiTi SMA

The accumulation of dislocation defect was generally recognized as the origin of residual strain and the pseudoelastic instability in NiTi shape memory alloys (SMAs). In the present work, the pseudoelastic instability was studied by comparing the characteristics of Lüders-type and uniform transformation mechanism via in-situ synchrotron-based high-energy X-ray diffraction (XRD) characterization. The experimental results showed that the Lüders-type mechanism could result in an intense and sharp increase of stress-induced martensite at the expense of austenite. The residual austenite with high lattice strain within the Lüders band might be fully martensitic beyond the stress plateau of the ε-σ curve. With the accumulation of dislocation defect, the uniform martensitic transformation took place by the progressively homogeneous nucleation and growth of martensite in a local region. While the residual martensite and dislocation density was stabilized during mechanical cycling, the deformation of NiTi SMA turned into a mixture of (i) a balanced forward and reverse phase transformation between austenite and martensite, as well as (ii) the elastic deformation of the aggregate. There was no apparent increase in dislocation density detected during further cycling.

Na3FeH7 and Na3CoH6: Hydrogen-Rich First-Row Transition Metal Hydrides from High Pressure Synthesis.

The formation of ternary hydrogen-rich hydrides involving the first-row transition metals TM = Fe and Co in high oxidation states is demonstrated from in situ synchrotron diffraction studies of reaction mixtures NaH–TM–H2 at p ≈ 10 GPa. Na3FeH7 and Na3CoH6 feature pentagonal bipyramidal FeH73– and octahedral CoH63– 18-electron complexes, respectively. At high pressure, high temperature (300 < T ≤ 470 °C) conditions, metal atoms are arranged as in the face-centered cubic Heusler structure, and ab initio molecular dynamics simulations suggest that the complexes undergo reorientational dynamics. Upon cooling, subtle changes in the diffraction patterns evidence reversible and rapid phase transitions associated with ordering of the complexes. During decompression, Na3FeH7 and Na3CoH6 transform to tetragonal and orthorhombic low pressure forms, respectively, which can be retained at ambient pressure. The discovery of Na3FeH7 and Na3CoH6 establishes a consecutive series of homoleptic hydrogen-rich complexes for first-row transition metals from Cr to Ni.

L-Lysine Amino Acid Adsorption on Zeolite L: a Combined Synchrotron, X-Ray and Neutron Diffraction Study.

Invited for this month's cover are the groups of Annalisa Martucci and Luisa Pasti at the University of Ferrara (Italy). The cover picture shows L-lysine amino acid adsorption on zeolite L. The role of zeolite channels in the stabilization of the lysine absorbed and the effect of water on protein structure are elucidated at atomistic level. The stabilization of the L α-helical conformation is related to strong H-bonds between the tail aminogroups of lysine molecules and the Brønsted acid site as well as to complex intermolecular H-bond system between water molecules, zeolite and amino acid. Read the full text of their Full Paper at 10.1002/open.202000183.

Na-Ni-H Phase Formation at High Pressures and High Temperatures: Hydrido Complexes [NiH5]3- Versus the Perovskite NaNiH3.

The Na–Ni–H system was investigated by in situ synchrotron diffraction studies of reaction mixtures NaH–Ni–H2 at around 5, 10, and 12 GPa. The existence of ternary hydrogen-rich hydrides with compositions Na3NiH5 and NaNiH3, where Ni attains the oxidation state II, is demonstrated. Upon heating at ∼5 GPa, face-centered cubic (fcc) Na3NiH5 forms above 430 °C. Upon cooling, it undergoes a rapid and reversible phase transition at 330 °C to an orthorhombic (Cmcm) form. Upon pressure release, Na3NiH5 further transforms into its recoverable Pnma form whose structure was elucidated from synchrotron powder diffraction data, aided by first-principles density functional theory (DFT) calculations. Na3NiH5 features previously unknown square pyramidal 18-electron complexes NiH53–. In the high temperature fcc form, metal atoms are arranged as in the Heusler structure, and ab initio molecular dynamics simulations suggest that the complexes are dynamically disordered. The Heusler-type metal partial structure is essentially maintained in the low temperature Cmcm form, in which NiH53– complexes are ordered. It is considerably rearranged in the low pressure Pnma form. Experiments at 10 GPa showed an initial formation of fcc Na3NiH5 followed by the addition of the perovskite hydride NaNiH3, in which Ni(II) attains an octahedral environment by H atoms. NaNiH3 is recoverable at ambient pressures and represents the sole product of 12 GPa experiments. DFT calculations show that the decomposition of Na3NiH5 = NaNiH3 + 2 NaH is enthalpically favored at all pressures, suggesting that Na3NiH5 is metastable and its formation is kinetically favored. Ni–H bonding in metallic NaNiH3 is considered covalent, as in electron precise Na3NiH5, but delocalized in the polyanion [NiH3]−.

Long-range oxygen ordering linked to topotactic oxygen release in Pr2NiO4+δ fuel cell cathode material

Complex oxygen ordering evidenced for the oxygen membrane cathode material Pr2NiO4.25 at room temperature with translational periodicities attaining almost 100 Å by single-crystal synchrotron diffraction studies.

Tuning of multiferroic order with Co doping in CuCr2O4 : Interplay between structure and orbital order

We observe a ferroelectric (FE) order in an unexplored ${\mathrm{CuCr}}_{2}{\mathrm{O}}_{4}$ with a reasonably high value of the FE Curie temperature $({T}_{\mathrm{FE}})$ at 170 K, which is also much higher than the magnetic ordering temperature. The systematic substitution of Jahn-Teller (J-T) active divalent Cu ion by a non-Jahn-Teller active divalent Co ion causes a systematic shift of ${T}_{\mathrm{FE}}$ from 170 K for $x=0$ to 146 K for $x=0.8$ in ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$. The values of electric polarization vary from 0.0665 $\ensuremath{\mu}{\mathrm{C}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}}^{\ensuremath{-}2}$ to 0.1704 $\ensuremath{\mu}{\mathrm{C}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}}^{\ensuremath{-}2}$, which is maximum for $x=0.6$, associated with the highest value of the coercivity. The synchrotron diffraction studies of the compounds with $x=0.2$ and 0.8 confirm that a structural transition to a polar $Ima2$ space group from the tetragonally distorted $I{4}_{1}/amd$ structure gives rise to the ferroelectricity. In all the members of ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ series, the ${T}_{\mathrm{FE}}$ is observed at much higher temperature than the corresponding magnetic ordering temperatures $({T}_{N})$. These results are in contrast to that of the reported results of ${T}_{\mathrm{FE}}l{T}_{N}$ for the end member with $x=1$ or ${\mathrm{CoCr}}_{2}{\mathrm{O}}_{4}$, where the J-T active ${\mathrm{Cu}}^{2+}$ is absent. We propose that the J-T distortion in the entire series with $0\ensuremath{\le}x\ensuremath{\le}0.8$ holds the key, where interplay between the J-T distortion driven orbital order and the structural distortion correlates tuning of the ${T}_{\mathrm{FE}}$ in ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$.