Neutron Powder Diffraction Study Research Articles

Display of converse and direct magnetoelectric effect in double perovskite LaYFe2O6

This work reports the simultaneous observation of converse magnetoelectric (CME) and direct magnetoelectric (DME) effects in LaYFe2O6. The structural, magnetic, and magnetoelectric properties of LaYFe2O6, prepared by the sol-gel auto-combustion method and sintered at various temperatures, have been studied. The x-ray powder diffraction study suggests the double perovskite structure with symmetries P21nm (∼90%) and Pbnm (∼10%). The alternate ordering of La and Y ions is confirmed by the neutron powder diffraction (ND) study, which also suggests the antiferromagnetic (AFM) ordering of spins. AFM behavior is also manifested by the magnetic field-dependent magnetization (M) measurement. A higher P21nm phase content is desirable in the context of magnetoelectricity. Magnetic transition (∼700 K) is asserted in the temperature-dependent M measurement. The isothermal magnetization study shows weak ferromagnetism probably due to gradually increasing spin canting with temperature until the transition temperature. The highest CME coefficient (∼2.26 mOe cm/V) as well as DME coefficient (∼0.45 mV/cm Oe) in this material are recorded. True magnetoelectricity for temperature as high as 400 K opens up a new avenue on the playground of magnetoelectric (ME)-based applications.

Interplay of spin, phonon, and lattice degrees in a hole-doped double perovskite: Observation of spin–phonon coupling and magnetostriction effect

Unlike a typical spin–phonon coupling, an exhibition of unconventional spin–phonon coupling, which is mediated via magnetostriction effect, is reported in a hole-doped double perovskite Pr1.5Sr0.5CoMnO6. Various investigations including electronic and crystal structures, spin structure, transport property, lattice dynamics, and theoretical density of states analysis by density-functional theory (DFT) have been performed. A substantial increase in the mean oxidation states of Co ions and a concurrent abrupt decrease in the resistivity upon Sr doping is observed, thus altering its underlying transport mechanism. An insulating and ferromagnetic (FM) ground state is predicted by DFT calculations. The neutron diffraction data analysis reveals a complex crystal structure of Pr1.5Sr0.5CoMnO6, which consists of B-site disordered monoclinic (P21/n) and orthorhombic (Pnma) structures, highlighting the presence of an anti-site disorder in the system. The analysis also suggests an overall FM ordering of Co/Mn spins below 150 K for the monoclinic phase, whereas no such magnetic ordering is found for the orthorhombic phase. More interestingly, the neutron powder diffraction study perceives the presence of a strong magnetostriction effect in the system. Raman spectroscopy unravels the presence of a spin–phonon coupling, which is essentially mediated by the magnetostriction effect.

An Easy‐to‐Use Custom‐Built Cell for Neutron Powder Diffraction Studies of Rechargeable Batteries

AbstractInvited for this month's cover is the group of Daniel R. Sørensen at the University of Aarhus (Denmark) and at the University of Lund (Sweden). The cover picture shows a battery cell designed for in operando neutron powder diffraction. The picture seeks to illustrate the experiment process where lithium ions are moving into the crystal structure of the battery cathode during discharge. This leads to changes in the crystal structure that are very important to understand for optimizing the battery materials. These structural changes are probed in operando by neutron powder diffraction, and neutrons are especially suited for probing the location of Li‐ion compared with similar techniques such as X‐ray diffraction. The beauty of using neutrons is also that their penetrating power allows for investigating the battery without the need for windows of any kind. Read the full text of their Research Article at 10.1002/cmtd.202200046.

Beyond the ionic radii: A multifaceted approach to understand differences between the structures of LnNbO4 and LnTaO4 fergusonites

Synchrotron X-ray powder diffraction methods have been used to obtain accurate structures of the lanthanoid tantalates, LnTaO4, at room temperature. Three different structures are observed, depending on the size of the Ln cation: P21/c (Ln = La, Pr), I2/a (Ln = Nd-Ho), and P2/c (Ln = Tb-Lu). BVS analysis indicated that TaV is six-coordinate in these structures, with four short bonds and two longer bonds. Synchrotron X-ray powder diffraction methods were also used to observe the impact of Ta doping on the orthoniobates, Ln(Nb1-xTax)O4 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Yb, and Lu). Where both the niobate and tantalate oxide were isostructural (fergusonite structure, space group I2/a), complete solid solutions were prepared. In these solid solutions, the unit cell volume decreases as the Ta content increases. The subtle interaction evident between the LnO8 and BO6 sublattices in the fergusonite-type oxides was not observed in the related pyrochlore oxides. A combined synchrotron X-ray and neutron powder diffraction study of the series Ho(Nb1-xTax)O4 was used to determine accurate atomic positions of the anions, and hence, bond lengths. This revealed a change in the (Nb/Ta)-O bond lengths, reflective of the difference in the valence orbitals of Nb(4d) and Ta(5d). Examination of the partial density of states demonstrates differences in the electronics between Nb and Ta, leading to a difference in the bandgap. This study highlights the importance of the long B-O contacts in the fergusonite structures, and its potential impact on the I2/a to I41/a phase transition.

An Easy‐to‐Use Custom‐Built Cell for Neutron Powder Diffraction Studies of Rechargeable Batteries

AbstractIn operando powder diffraction remains one of the most powerful tools for non‐destructive investigation of battery electrode materials. While in operando X‐ray, especially synchrotron radiation, powder diffraction is by now a routine experimental technique, in operando neutron powder diffraction is still less established. We present a new electrochemical cell for in operando neutron powder diffraction, which is, first and foremost, easy to use, but can also cycle electrode materials under electrochemical conditions close to those achieved using standard laboratory cells. The cell has been designed in multiple sizes, and high‐quality electrochemical and neutron powder diffraction data is presented for sample sizes as low as 48 mg total active material. The cell handles lithium‐ion and sodium‐ion materials equally well, with no difference in how the cell is prepared and assembled. The cell is intended to be used as sample environment at powder diffractometers at the neutron facilities MLZ, ORNL and ACNS.

Experimental and computational insights into the anomalous thermal expansion of (NH4)ReO4

The temperature dependence of the structure and the ground state properties of scheelite-type NH4ReO4 have been studied using neutron powder diffraction (NPD) and Density Functional Theory (DFT), respectively. Despite the large incoherent background in the experimental NPD, associated with the presence of hydrogen, accurate and precise structural parameters were obtained. Comparison of the results of the NPD and DFT studies shows that the observed anomalous thermal contraction in NH4ReO4 is a consequence of thermally induced rotational disorder of the NH4 groups. Comparing the experimentally determined and optimized structures reveals deformation of the NH4 tetrahedra that is responsible for the unusual tetragonal distortion of this material. The Raman spectra of NH4ReO4 is presented and the modes are assigned based on the DFT calculations.

Neutron diffraction study of nitride perovskite LaReN3

AbstractNitride perovskites ABN3 are extremely rare with only two known instances of bulk‐phase materials, ThTaN3 and LaReN3. Here, we present a powder neutron diffraction study of the recently‐reported nitride perovskite LaReN3. A full structural model of LaReN3 at 300 K ( , a=5.58523(5), b=5.59297(5), c=7.90419(6) Å, α=89.9170(8), β=90.1729(7), γ=90.1709(7)°) has been refined simultaneously against powder neutron and previously‐collected synchrotron X‐ray diffraction data. This indicates that the triclinic distortion is due to cooperative electronic distortions of ReN6 octahedra, and also demonstrates that all nitrogen positions are fully occupied so the sample is stoichiometric LaReN3. Lattice strains derived from fits to variable temperature powder neutron data from 5 to 300 K indicate that LaReN3 undergoes structural transitions to higher symmetry perovskite tilt structures between 300 and 350 K.

(Digital Presentation) Understanding of Fast Charging in Li-Ion Batteries, an Operando Neutron Diffraction Study

Fast charging (<15 min) of lithium-ion batteries (LIBs) for electrical vehicles (EVs) is widely seen as the key factor that will greatly stimulate the EV markets, and its realization is mainly hindered by the sluggish diffusion of Li+. To have a mechanistic understanding of Li+ diffusion within LIBs, in this study, structural evolutions of electrodes for a Ni-rich LiNi0.6Mn0.2Co0.2O2 (NMC622) || graphite cylindrical cell with high areal loading are developed for operando neutron powder diffraction study at different charging rates. Via sequential Rietveld refinements, changes in structures of NMC622 and Li x C6 are obtained during moderate and fast charging (from 0.27 C to 4.4 C). NMC622 exhibits the same structural evolution regardless of C-rates. For phase transitions of Li x C6, the stage I (LiC6) phase emerges earlier during the stepwise intercalation at a lower state of charge when charging rate is increased. It is also found that the stage II (LiC12) → stage I (LiC6) transition is the rate-limiting step during fast charging. The LiC12 → LiC6 transition mechanism is further analyzed using the Johnson–Mehl–Avrami–Kolmogorov model. It is concluded as a diffusion-controlled, 1D phase transition with decreasing nucleation kinetics under increasing charging rates.

High-Pressure Structural Behavior of para-Xylene

A high-pressure neutron powder diffraction study was conducted on perdeuterated para-xylene (C8D10). para-Xylene crystallizes in the monoclinic crystal system (space group P21/n) at ambient temperature and ca. 0.1 GPa. The structure is consistent with the known low-temperature form. No further phase transitions were observed in the pressure range 0.11(1)–4.72(2) GPa. A complementary high-pressure single-crystal diffraction experiment was performed on hydrogenous para-xylene confirming the assigned space group P21/n. An isothermal equation of state was obtained [bulk modulus, B0 = 3.5(4) GPa] and structural changes of the material have been investigated as a function of pressure. This experimental study is supported by dispersion-corrected density functional theory calculations.

Neutron powder-diffraction study of phase transitions in strontium-doped bismuth ferrite: 1. Variation with chemical composition

We report results from a study of the crystal and magnetic structures of strontium-doped BiFeO3 using neutron powder diffraction and the Rietveld method. Measurements were obtained over a wide range of temperatures from 300–800 K for compositions between 10%–16% replacement of bismuth by strontium. The results show a clear variation of the two main structural deformations—symmetry-breaking rotations of the FeO6 octahedra and polar ionic displacements that give ferroelectricity—with chemical composition, but relatively little variation with temperature. On the other hand, the antiferromagnetic order shows a variation with temperature and a second-order phase transition consistent with the classical Heisenberg model. There is, however, very little variation in the behaviour of the antiferromagnetism with chemical composition, and hence with the degree of the structural symmetry-breaking distortions. We therefore conclude that there is no significant coupling between antiferromagnetism and ferroelectricity in Sr-doped BiFeO3 and, by extension, in pure BiFeO3.

The Structure, Magnetic and Magnetotransport Properties of Sr 1− x Y x CoO 3− δ Layered Cobaltites

The properties of Sr1−xYxCoO3−δ layered cobaltites are determined by synchrotron X-ray and neutron powder diffraction studies, by measurements of magnetic and magnetotransport properties. It is shown that the crystal structure changes from tetragonal P4/mmm (ap × ap × 2ap) to monoclinic A2/m (4√2ap × 2√2ap×4ap up to the magnetic ordering temperature and 2√2ap ×2√2ap × 4ap above) through the intermediate tetragonal I4/mmm (2ap × 2ap × 4ap) with alternating layers of CoO6 and CoO4+δ. The basic magnetic structure is G-type antiferromagnetic with Co3+ ions in a high spin/low spin (HS/LS) state mixture in both structural layers. The Co3+ magnetic moments in the CoO6 and CoO4+δ layers are 1.5 μB/Co and 2 μB/Co for x = 0.1 and 1.8 μB/Co and 2.7 μB/Co for x = 0.2, respectively. The antiferromagnetic–“ferromagnetic” transition in compounds with x > 0.2 is associated with the structural and orbital disorder. Magnetic transitions are accompanied by structural phase transitions. The presence of the ferromagnetic component is associated with the monoclinic distortions and canting of magnetic moments in anion-deficient layers due to orbital ordering. A sharp drop of the magnetization for x > 0.2 is caused by the LS Co3+ stabilization and orbital disordering. No spontaneous magnetization is found for compounds with x > 27%.

Pressure Tuning the Jahn-Teller Transition Temperature in NaNiO2.

NaNiO2 is a layered material consisting of alternating layers of NaO6 and Jahn–Teller-active NiO6 edge-sharing octahedra. At ambient pressure, it undergoes a broad phase transition from a monoclinic to rhombohedral structure between 465 and 495 K, associated with the loss of long-range orbital ordering. In this work, we present the results of a neutron powder diffraction study on powdered NaNiO2 as a function of pressure and temperature from ambient pressure to ∼5 GPa between 290 and 490 K. The 290 and 460 K isothermal compressions remained in the monoclinic phase up to the maximum pressures studied, whereas the 490 K isotherm was mixed-phase throughout. The unit-cell volume was fitted to a second-order Birch–Murnaghan equation of state, where B = 119.6(5) GPa at 290 K. We observe at 490 K that the fraction of the Jahn–Teller-distorted phase increases with pressure, from 67.8(6)% at 0.71(2) GPa to 80.2(9)% at 4.20(6) GPa. Using this observation, in conjunction with neutron diffraction measurements at 490 K on removing pressure from 5.46(9) to 0.342(13) GPa, we show that the Jahn–Teller transition temperature increases with pressure. Our results are used to present a structural pressure–temperature phase diagram for NaNiO2. To the best of our knowledge, this is the first diffraction study of the effect of pressure on the Jahn–Teller transition temperature in materials with edge-sharing Jahn–Teller-distorted octahedra and the first variable-pressure study focusing on the Jahn–Teller distortion in a nickelate.

Maximizing acetylene packing density for highly efficient C2H2/CO2 separation through immobilization of amine sites within a prototype MOF

• A new strategy to maximize the acetylene packing density has been developed. • The CAU-10-NH 2 exhibits very high C 2 H 2 /CO 2 selectivity with low Qst. • Recognition mechanism has been revealed by neutron powder diffraction. For practical separation applications, porous sorbents with high separation performance, low heat of adsorption, high stability and low production cost are highly desired. A plausible strategy is herein developed through immobilization of amine sites in a prototype MOF for maximized packing density and selectivity. The CAU-10-NH 2 material exhibits high packing density of 0.46 cm 3 /g, C 2 H 2 adsorption capacity (4.1 mmol/cm 3 , at 0.5 bar), and high C 2 H 2 /CO 2 selectivity of 10.8, which outperformed the unfunctionalized benchmark material CAU-10-H. Neutron powder diffraction study reveals the formation of densely packed C 2 H 2 as tetrameric clusters in the pore. The separation performance of CAU-10-NH 2 well remains in column separation conditions, with a remarkable dynamic selectivity of 10.9. The good water-stability and one-step synthesis from commercially available precursors make this material a promising candidate for practical C 2 H 2 /CO 2 separation.

Neutron powder diffraction study of the phase transitions in deuterated methylammonium lead iodide

We report the results of a neutron powder diffraction study of the phase transitions in deuterated methylammonium lead iodide, with a focus on the system of orientational distortions of the framework of PbI6 octahedra. The results are analysed in terms of symmetry-adapted lattice strains and normal mode distortions. The higher-temperature cubic–tetragonal phase transition at 327 K is weakly discontinuous and nearly tricritical. The variations of rotation angles and spontaneous strains with temperature are consistent with a standard Landau theory treatment. The lower-temperature transition to the orthorhombic phase at 165 K is discontinuous, with two systems of octahedral rotations and internal distortions that together can be described by 5 order parameters of different symmetry. In this paper we quantify the various symmetry-breaking distortions and their variation with temperature, together with their relationship to the spontaneous strains, within the formalism of Landau theory. A number of curious results in the low-temperature phase are identified, particularly regarding distortion amplitudes that decrease rather than increase with lowering temperature.

Ammonia Mono Hydrate IV: An Attempted Structure Solution

The mixed homonuclear and heteronuclear hydrogen bonds in ammonia hydrates have been of interest for several decades. In this manuscript, a neutron powder diffraction study is presented to investigate the structure of ammonia monohydrate IV at 170 K at an elevated pressure of 3–5 GPa. The most plausible structure that accounts for all features in the experimental pattern was found in the P21/c space group and has the lattice parameters a=5.487(3) Å, b=19.068(4) Å, c=5.989(3) Å, and β=99.537(16) deg. While the data quality limits discussion to a proton-ordered structure, the structure presented here sheds light on an important part of the ammonia–water phase diagram.

Synthesis and characterisation of the crystal structure and magnetic ordering of double perovskite La3Co2MoO9

The crystal structural and magnetic properties of the La3Co2MoO9 double perovskite ceramic sample have been studied by X-ray and neutron powder diffraction and magnetometry. Structural investigation indicated that sample is monoclinic perovskite with space group P21/n and unit cell parameters of a=5.5812(2) Å, b=5.7073(2)) Å, c=7.9279(3) Å, β=89.96(2)o, V=252.558(11)Å3 at room temperature. The two crystallographically-distinct 2d and 2c octahedral positions are occupied ordered by Co2+ (2d position) and Co2+ and Mo5+/Mo4+ (2c-position). Magnetometry data together with neutron powder diffraction study has shown that this perovskite is the ferrimagnetic (TC=147 K) with the uncompensated magnetic moment of 2 μB and the high value of coercive force HC (HC=75 kOe at 4.2 K}.

Doping site induced alteration of incommensurate antiferromagnetic ordering in Fe-doped MnNiGe alloys

The magnetic structure of Fe-doped MnNiGe alloys of nominal compositions ${\mathrm{MnNi}}_{0.75}{\mathrm{Fe}}_{0.25}\mathrm{Ge}$ and ${\mathrm{Mn}}_{0.85}{\mathrm{Fe}}_{0.15}\mathrm{NiGe}$ has been explored through detailed neutron powder diffraction (NPD) study in ambient and high-pressure (6 kbar) conditions. Both these alloys crystallize with ${\mathrm{Ni}}_{2}\mathrm{In}$-type hexagonal structure (with $P{6}_{3}/mmc$ space group) at room temperature and undergo a martensitic transition to low-temperature TiNiSi-type orthorhombic structure (with space group $Pnma$). Both the alloys show incommensurate antiferromagnetic ordering at the low-temperature martensitic phase. However, the modulation of the magnetic structures depends strongly on the doping site of Fe. The incommensurate propagation vector $\mathbf{k}$ for ${\mathrm{MnNi}}_{0.75}{\mathrm{Fe}}_{0.25}\mathrm{Ge}$ and ${\mathrm{Mn}}_{0.85}{\mathrm{Fe}}_{0.15}\mathrm{NiGe}$ alloys are found to be (0.1790(1),0,0) and (0.1543(3),0,0), respectively at 1.5 K, and these remain almost unchanged with increasing sample temperature under ambient conditions. The application of the external pressure results in a significant effect on both martensitic transition temperature and low-temperature magnetic structure. The propagation vectors $\mathbf{k}$ for both the alloys show a monotonic decrease with increasing sample temperature in the presence of external pressure. Interestingly, no sign of the magnetically ordered hexagonal austenite phase was observed in any alloys down to the lowest measurement temperature.

Structural Evolution and Transition Dynamics in Lithium Ion Battery under Fast Charging: An Operando Neutron Diffraction Investigation.

Fast charging (<15 min) of lithium‐ion batteries (LIBs) for electrical vehicles (EVs) is widely seen as the key factor that will greatly stimulate the EV markets, and its realization is mainly hindered by the sluggish diffusion of Li+. To have a mechanistic understanding of Li+ diffusion within LIBs, in this study, structural evolutions of electrodes for a Ni‐rich LiNi0.6Mn0.2Co0.2O2 (NMC622) || graphite cylindrical cell with high areal loading (2.78 mAh cm−2) are developed for operando neutron powder diffraction study at different charging rates. Via sequential Rietveld refinements, changes in structures of NMC622 and Li x C6 are obtained during moderate and fast charging (from 0.27 C to 4.4 C). NMC622 exhibits the same structural evolution regardless of C‐rates. For phase transitions of Li x C6, the stage I (LiC6) phase emerges earlier during the stepwise intercalation at a lower state of charge when charging rate is increased. It is also found that the stage II (LiC12) → stage I (LiC6) transition is the rate‐limiting step during fast charging. The LiC12 → LiC6 transition mechanism is further analyzed using the Johnson–Mehl–Avrami–Kolmogorov model. It is concluded as a diffusion‐controlled, 1D phase transition with decreasing nucleation kinetics under increasing chargingrates.

Effects of Ti substitution for Zr on the electrochemical characteristics and structure of AB2-type Laves-phase alloys as metal hydride anodes

The structural composition and electrochemical capacity of four AB2 Laves-type intermetallic alloys with various Ti/Zr ratios (TixZr1−xLa0.03Ni1.2Mn0.7V0.12Fe0.12, x = 0.12, 0.15, 0.18, and 0.22) were investigated in this study. The alloys were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. These data revealed the coexistence of the main phase of the C15-type FCC Laves-type AB2 compounds with a secondary La–Ni intermetallic that was present in minor amounts. Increasing the Ti substitution for Zr caused the gradual shrinkage of the unit cells of the C15 phase. The neutron powder diffraction studies demonstrated that in the trihydride (Ti, Zr, V)(Ni, Mn, Fe, V)2D3.2, D atoms filled A2B2 tetrahedra, whereas V atoms occupied not only conventional 16d sites but also partially replaced Zr/Ti at 8a sites. All studied alloys showed similar activation behaviors, wherein four cycles were required to realize the highest electrochemical capacity of the anodes. The Ti12/Zr88 alloy demonstrated excellent full discharge capacity that reached 466 mAh/g. The Ti22/Zr78 alloy electrode exhibited good cycling stability (retention rate of ~71%) after 500 cycles and a superior high-rate discharge capability (retention rate of ~71%) at a discharge current density of 400 mA/g. The cycling of the Ti22/Zr78 alloy electrode was studied by electrochemical impedance spectroscopy (EIS) to understand the reasons for the deterioration of cycling capacity, which was related with the pulverization of the alloys and increase in irreversible capacity.

Neutron powder diffraction studies of magnetic transitions in Fe-based orthorhombic perovskites

Neutron powder diffraction studies of magnetic transitions in Fe-based orthorhombic perovskites