TOF Neutron Powder Diffraction Research Articles

Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

Summary O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

Jahn-Teller and geometric frustration effects on the structural and magnetic ground states of substituted spinels (Ni,A)Cr2O4 (A = Mn/Cu)

Comparative study of the effects of substitution (25%) of Jahn-Teller (JT) active Cu2+ and non JT active Mn2+ cations, at the Ni2+ site, on the geometric frustration (GF) and cooperative JT distortion (CJTD) in multiferroic NiCr2O4 has been carried out with the help of low-temperature magnetization, x-ray diffraction and time of flight (TOF) neutron powder diffraction (NPD) measurements. On Mn2+ substitution the CJTD, which causes elongation of the NiO4 tetrahedra in I41/amd phase of NiCr2O4, gets suppressed at room-temperature (RT) and stabilizes the Fd-3m phase in (Ni0.75Mn0.25)Cr2O4. On the contrary the Cu2+ substitution inverts the effect of CJTD and the tetrahedra get flattened at RT, which in turn oppositely distorts the I41/amd lattice in Ni0.75Cu0.25Cr2O4. The frustration index decreases on substitution. Intriguingly, the tetragonal to orthorhombic phase transition and the antiferromagnetic ordering, which are clearly evident in the pristine NiCr2O4 and the Cu2+ substituted sample respectively at 30 K and 70 K, have not been observed for the Mn2+ substituted sample. This has been attributed to the change in Cr3+- Cr3+ direct magnetic-interaction on structural transition. However, the long-range ferrimagnetic order remains intact for all the three compositions i.e. NiCr2O4, Ni0.75Mn0.25Cr2O4 and Ni0.75Cu0.25Cr2O4 occurring at 75 K, 70 K and 95 K, respectively. The Mn2+ substituted compound shows short-range magnetic correlation at low-temperatures, as evident from the diffuse and broad hump in the intensity-vs-d spacing plot of TOF NPD data. This short-range magnetic order has been attributed to the known spiral magnetic order.

Synthesis of large and homogeneous single crystals of water-bearing minerals by slow cooling at deep-mantle pressures

The presence of water in the Earth’s deep mantle is an issue of increasing interest in the field of highpressure mineralogy. An important task for further advancing research in the field is to create homogeneous single crystals of candidate deep-mantle water-bearing minerals of 1 mm or larger in size, which is required for applying them for the time-of-flight (TOF) single-crystal Laue diffraction method with a third-generation neutron instrument. In this study, we perform several experiments to demonstrate an improved methodology for growing hydrous crystals of such large sizes at relevant transition zone and lower-mantle conditions via very slow cooling over a maximum period of 1 day. Successfully synthesized crystals using this methodology include dense hydrous magnesium silicate (DHMS) phase E, hydrous wadsleyite, hydrous ringwoodite, and bridgmanite (silicate perovskite). It is also demonstrated that these hydrous crystals can be grown from deuterium enriched starting materials in addition to those having a natural hydrogen isotope ratio. Magnitudes of chemical and crystallographic heterogeneities of the product crystals were characterized by comprehensive analysis of X-ray precession photography, single-crystal X-ray diffraction (SCXRD), field-emission scanning electron microscope (FE-SEM), electron probe microanalyzer (EPMA), secondary ion mass spectroscopy (SIMS), powder X-ray diffraction (PXRD), and TOF neutron powder diffraction (TOF-NPD). The product crystals were confirmed to be inclusion free and crystallographically homogeneous. Compositional and isotopic differences of major elements and hydrogen isotope abundances were lower than 1 and 3%, respectively, among intracrystals and intercrystals within each recovered sample capsule. Phase E crystals up to 600 μm in the largest dimension were grown at a constant temperature of 1100 °C kept for 3 h. Using a lattice parameter-to-temperature relation of phase E, the thermal gradient in the sample capsules for the phase E synthesis has been evaluated to be 20 °C/mm. Hydrous wadsleyite crystals up to 1100 μm in the largest dimension were grown at 1390 °C with a temperature reduction of 70 °C during heating for 10 h. Hydrous ringwoodite crystals up to 1000 μm in the largest dimension were grown at around 1400 °C with a temperature reduction of 110 °C during heating for 12 h. Bridgmanite crystals up to 600 μm in the largest dimension were grown at 1700 °C with a temperature reduction of 30 °C during heating for 12 h. A TOF single-crystal diffraction instrument has been successfully used for analyzing one of the hydrous wadsleyite crystals, which demonstrated that single crystals appropriate for their expected usage are created using the method proposed in the present study.

The birth of time‐of‐flight (TOF) neutron powder diffraction at pulsed neutron source (invited)

Behind every improvement there is a story.The early history of the TOF neutron powder diffraction technique is presented. Successes and problems in the application of this technique in material science are reported. Powder diffraction technique is very useful when materials, in a single crystal form, reveal complicated electric and magnetic domain structures. Finding and describing the magnetic structure of multiferroics is the great success of ultra‐high resolution TOF neutron diffraction. This unique role of the TOF method in discovery of the modulated magnetic structure of BiFeO3 is presented. To date, the TOF powder neutron diffraction technique gives the richest information on the long period modulated magnetic structure of BiFeO3 and its solid solutions. Determination of magnetic moment direction in a crystal lattice is the unique area of application of the TOF technique. The current status and perspectives of the application of the TOF neutron powder diffraction technique in material science are presented in the review.

Synthesis and characterization of perovskite-type SrxY1−xFeO3−δ (0.63≤x

Oxygen-deficient ferrates with the cubic perovskite structure SrxY1−xFeO3−δ were prepared in air (0.71≤x≤0.91) as well as in N2 (x=0.75 and 0.79) at 1573K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3−δ=2.79(2) for x=0.75 to 3−δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along 〈100〉p with G± ∼0.4〈100〉p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5–390K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5ppm/K in air at 298–673K. At 773–1173K TEC increases up to 17.2ppm/K due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1−yMyO3−δ (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79.

Ionic Conductivity and Structural Properties of Lithium Lanthanum Titanate Quenched into Liquid Nitrogen Studied by Neutron Powder Diffraction

For 7 Li-enriched La 2/3- x 7 Li 3 x TiO 3 samples quenched into liquid nitrogen and cooled in the furnace, impedance measurements and time-of-flight neutron powder diffraction (TOF-NPD) experiments were carried out in order to study the effect of the quenched-into-liquid-nitrogen treatment for the ionic conduction and the structural properties. It was found that the quenched-into-liquid-nitrogen treatment enhances the lithium ionic conductivity in the 7 Li-content range between 3 x ∼0.25 and 0.45. Furthermore, the local structure within 6 A did not change, according to the atomic pair density function (PDF) analysis.

Crystal Structure of Li7P3S11Studied by Neutron and Synchrotron X-ray Powder Diffraction

Time-of-flight neutron powder diffraction (TOF-NPD) and synchrotron X-ray powder diffraction (SXPD) experiments were carried out to study the crystal structure of 7 Li isotope enriched 7 Li 7 P 3 S 11 glass ceramics, which is a lithium superionic conductor. Combined X-ray/neutron Rietveld refinement informed us precise atomic coordinates, especially lithium. Furthermore, a network of neighboring Li + cations was visualized in the crystal structure of Li 7 P 3 S 11 with the triclinic system (space group: P 1 ) in order to predict the diffusion pathway of Li + cations.

Oxygen Non‐Stoichiometry and Thermal–Chemical Expansion of Ce0.8Y0.2O1.9−δ Electrolytes by Neutron Diffraction

A dense tubular solid electrolyte with the composition Ce0.8Y0.2O1.9−δ (CY20) was prepared. In situ time‐of‐flight neutron powder diffraction (TOF‐ND) was performed at 900°C in the oxygen partial pressure pO2 range from 10−1–10−18 atm, and TOF‐ND data were analyzed by the Rietveld method. Diffraction data showed that the lattice parameter moderately increased with decreasing pO2 in the range of pO2>10−14 atm, while a dramatic expansion (∼0.6%) of the fluorite structure occurred at a pO2 of 10−18 atm. By refining all reasonable structural parameters, an approximately linear relationship between lattice parameter and oxygen vacancy δ was observed, resulting in ɛc/δ=0.08 and corresponding to δ=0.10 at a pO2 of 10−18 atm, all in agreement with the data published in the literature. The relative change in lattice parameter Δa/a followed a −1/4 power relation with pO2 in a low‐pO2 regime. As several (often strongly correlated) structural parameters can affect the intensities in ND profiles, care was taken to select refinement variables. It was found that O atom thermal factors for CY20 increased as the oxygen vacancy concentration and lattice expansion increased.

Synthesis, crystal structure, and magnetic properties of new layered hexagonal perovskite Ba8Ta4Ru8/3Co2/3O24

A new hexagonal perovskite-type oxide Ba8Ta4Ru8/3Co2/3O24 was synthesized by the solid-state method at 1573K and characterized by electron diffraction (ED), time-of-flight (TOF) neutron powder diffraction, and magnetic susceptibility. Structure parameters of Ba8Ta4Ru8/3Co2/3O24 were refined by the Rietveld method from the TOF neutron powder diffraction data on the basis of space group P63/mcm and lattice parameters a=10.0075(1)Å and c=18.9248(2)Å as obtained from the ED data (Z=3). The crystal structure of Ba8Ta4Ru8/3Co2/3O24 consists of 8-layered (cchc)2 close-packed stacking of BaO3 layers along the c-axis. Corner-shared octahedra are filled by Ta only and face-shared octahedra are statistically occupied by Ru, Co, and vacancies. Similar compounds Ba8Ta4Ru8/3M2/3O24 with M=Ni and Zn were also prepared. Magnetic susceptibility measurements showed no magnetic ordering down to 5K.

New Frontiers of Materials Science and Engineering by the J-PARC Neutron Powder Diffractometers

New frontiers by the new neutron powder diffractometers in the JSNS/J-PARC facility have beendiscussed on the basis of the research works by the author and coworkers. The versatile new powder diffractometer SuperSirius should contribute to all the scientists and engineers in materials science and engineering with the help of supporting staffs. A very high-resolution neutron powder diffractometer can open new frontiers of materials science and engineering, because very small split of peaks with similar positions can be detectable, leading to considerable improvement of the accuracy of crystal parameters and phase transition temperature. Developments of the MEM analysis for the TOF neutron powder diffraction data are required. Short wavelength angle-dispersive type diffractometer is also necessary.

Synchrotron X-ray and TOF neutron powder diffraction study of a lyonsite-type oxide Co3.6Fe3.6(VO4)6

Co 3.6 Fe 3.6 (VO 4 ) 6 was synthesized by solid-state reaction at 900 °C, and its structure was determined by X-ray and neutron powder diffraction. Co 3.6 Fe 3.6 (VO 4 ) 6 is isotypic with lyonsite (space group: Pnma; Z =2), having lattice parameters of a =4.96480(9) Å, b =10.2245(2) Å, and c =17.2100(3) Å. Its structure parameters were refined by the Rietveld method with two sets of synchrotron X-ray (wavelengths: 0.85001 and 1.74500 Å) and time-of-flight neutron powder diffraction data. Co 2+ and Fe 3+ ions are distributed among three different metal sites M 1– M 3. Not Co 2+ ions but Fe 3+ ions are mainly contained in face-sharing M 3O 6 octahedra, forming single chains parallel to the [1 0 0] direction. Edge- and corner-sharing octahedra M 2O 6 build up layers perpendicular to the [0 0 1] direction. Edge-sharing trigonal prisms M 1O 6 form zig-zag single chains along the [1 0 0] direction. The M 1 and M 3 sites are about 6.0(2)% and 34.0(2)% deficient, respectively. The tendency for Co 2+ and Fe 3+ ions to distribute among the three metal sites is discussed on the basis of the electrostatic valence rule. Graphic

Synthesis and structures of lithium manganese oxide spinel, LiMn 2O 4− δ (0≤ δ≤0.27)

Lithium manganese oxides spinels were synthesized under various synthesis conditions and their structures were determined by TOF neutron powder diffraction measurements. Oxygen vacancies exist for the samples synthesized above 800°C, and the amount of vacancies was found to be sensitive to the synthesis conditions. The nearly stoichiometric spinels were synthesized at 750°C in O 2 followed by heating at 470°C. The transition temperatures of the cubic–orthorhombic transitions and the magnetic properties varied with the compositions. The stoichiometric spinel showed no cubic–orthorhombic phase transition.

The structures of the Ce and La N-phases RE3Si8 – xAlxN11 – xO4 + x (x≈ 1.75 for RE = Ce, x ≈ 1.5 for RE = La), determined by single-crystal X-ray and time-of-flight neutron powder diffraction, respectively

Single crystals of the sialon Ce N-phase Ce3Si8 − xAlxN11 − xO4 + x (x ≈ 1.75) were obtained via a novel route, i.e. by first preparing a fully compacted body with phase constitutions far away from thermal dynamic equilibrium by means of a fast densification technique, spark plasma sintering, and then heat treating this compact in a sialon powder bed at 1600 °C in N2 atmosphere for 24 h. The structure of the Ce N-phase was solved using MoKα single-crystal data and direct methods. It was refined in space group I2/a with a = 15.798(1), b = 4.8939(3), c = 17.990(1) Å, β = 114.816(4)°, V = 1262.4 Å3, to a weighted R(Fobs2) = 6.7% for 977 unique reflections. The isostructural La phase structure was refined with anisotropic thermal parameters for La and N/O atoms using time-of flight neutron powder diffraction data. The structure exhibits three structural kinds of N/O anions: 4/15 of these are N atoms which are triangularly coordinated by 3 Si/Al atoms, 2/15 are tetrahedron free apex O atoms which are in addition bonded to 3 Ce/La atoms while the remaining 9/15 are on sites that are statistically occupied by N and O atoms and which are bonded to 2 tetrahedral Si/Al atoms and 1–2 Ce/La atoms. Comparisons are made with a previous structural proposal deduced from solid state nuclear magnetic resonance spectra.

TOF neutron powder diffraction study of the helimagnetic structures in the Cr xFe 1− xVO 4-I system

The use of cold neutrons for long d-spacing time-of-flight neutron diffraction allows high-resolution data to be obtained for the solution and Rietveld refinement of complex magnetic structures. We have used the OSIRIS diffractometer at ISIS to collect data for Cr x Fe 1− x VO 4-I compounds with x=0.30, 0.35, 0.40 and 0.45 down to 2 K. The compounds order with a helimagnetic structure indexed by a propagation vector (0, k y, 1 2 ) , analogous to the previously reported x=0.25 and 0.50 samples. Our Rietveld refinements show that k y varies as a smooth function of x, which indicates that the structures are not locked into simple commensurate configurations. An alteration of the moment directions in the models reported for the x=0.25 and 0.50 magnetic structures was necessary in order to account for this high-resolution data.

Composite Copper Chalcogenide Halides: Neutron Powder Diffraction of CuClCu2TeS3 and Electrical Properties of CuClCu2TeS3, (CuI)2Cu3SbS3, and (CuI)3Cu2TeS3

The crystal structure of CuClCu2TeS3 was refined from TOF neutron powder diffraction data in order to verify the distribution of chlorine and sulfur. It is a novel derivative of the zincblende type with an ordered distribution both of the cations Cu+ and Te4+ and of the anions Cl− and S2−. The compound crystallizes in the rhombohedral system, space group R3m (No. 160) with a=7.3502(1) Å, c=10.3873(2) Å, V=485.99 Å3, and Z=3. The structure refinement converged to Rwp=0.039 and RBragg=0.032. From the neutron data it can be derived that there is no significant disorder of Cl and S atoms. Impedance spectroscopic measurements in the temperature range 140–280°C reveal that CuClCu2TeS3 is a semiconductor with an activation energy of 0.75 eV (T<200°C) and 1.25 eV (T>200°C), respectively. On the other hand (CuI)3Cu2TeS3 and (CuI)2Cu3SbS3 exhibit high copper ion conductivity with activation energies of 0.2 and 0.35 eV, respectively, but a negligible electronic conduction.

TOF neutron powder diffraction studies on f-electron systems

The occurrence of quadrupolar ordering in tetragonal TmAu 2 was investigated by neutron powder diffraction. The present work revealed that a structural transition to an orthorhombic form occurs simultaneously. CeCu 6 is a typical dense Kondo lattice compound. Appearance of a new Kondo state in CeInCu 5 was studied crystallographically. The structure parameters of CeInCu 5 show that only one of 4c sites of space group Pnma is fully occupied by In and that the rest of the four sites are completely by Cu. The decrease in one of the CeCu(5) distances on In doping was found, which might be related to the enhancement of T K.

Neutron Diffraction Study of LiNi0.8Mn0.2O2

Structure of the layered oxide, LiNi0.8Mn0.2O2, was determined by TOF neutron powder diffraction using space groupR3m. Its ionic distribution was determined to be [Li0.956Ni0.044]3a–(Ni0.791Mn0.209)3bO2. Slightly higher temperature of the synthesis caused the disordered arrangement of the Ni ions in the Li 3asites. Nevertheless, the manganese ions introduced into the lattice were situated only at the Ni sites. The structural changes caused by the manganese substitution are clarified, and the relationship between the ionic distribution and the cathodic properties of the lithium cells is discussed.

Electrical properties and crystal structures of the homologous series of oxides Nd 2Ba 2Ca mCe nTi 2−δCu 2+δO 11+ m+2 n ( m, n = 0 or 1)

Four oxides belonging to the homologous series with the general formula Nd 2Ba 2Ca m Ce n Ti 2−δCu 2+δO 11+ m+2 n , were prepared for m, n = 0 or 1. Although all of these oxides have two-dimensional CuO 2 planes, they do not show any superconductivity, only a normal paramagnetic behavior. Their crystal structures were analyzed by TOF neutron powder diffraction. Nd 2Ba 2Ti 1.908Cu 2.092O 11 ( m=0, n=0 and δ=0.09) is isomorphous with Gd 2Ba 2Ti 2Cu 2O 11. The structures of the other three oxides can be derived from that of Nd 2Ba 2Ti 1.908Cu 2.092O 11. The structure of Nd 2Ba 2Ti 1.92Cu 2.08O 12 ( m=1, n=0 and δ=0.08) is obtained by the substitution of rock-salt-type (Ca,Nd,Ba)O(Ca,Nd,Ba)O layers for the (Nd,Ba)O layer. The structure of Nd 2Ba 2CeTi 2Cu 2O 13 ( m=0, n=1 and δ=0) is characterized by the insertion of fluorite-type (Nd,Ce)O 2(Nd,Ce) layers in the place of the Nd layer. Nd 2Ba 2CaCeTi 2Cu 2O 14 ( m=1, n=1, and δ=0) results from the alternate substitutions of rock-salt-type and fluorite-type layers for the (Nd,Ba)O and Nd layers, respectively.

Relationship between Covalence and Displacive Phase Transition Temperature in RAO4 and LiAO3 (R = Rare-Earth Element and A = Nb and Ta)

Crystal structure analyses by TOF neutron powder diffraction are performed for RTaO4 (R = rare-earth element) and the Ta-O interatomic distances are determined. The relationship between the covalency of A -O bonds (A = Nb and Ta), which show the most shortening upon phase transition, and the transition temperature is discussed for RA O4 and LiAO3, and the parameters of Ta-O covalence are determined.

Applications of TOF neutron powder diffraction to high-Tc superconductors

Applications of TOF neutron powder diffraction to high-Tc superconductors