Neutron Powder Diffractometry Research Articles

Extraction of Hydrogen Location in Molecular Crystals in Spin-Contrast-Variation Neutron Powder Diffractometry

Extraction of Hydrogen Location in Molecular Crystals in Spin-Contrast-Variation Neutron Powder Diffractometry

Development of spin-contrast-variation neutron powder diffractometry for extracting the structure factor of hydrogen atoms

A spin-contrast-variation neutron powder diffractometry technique that extracts the structure factor of hydrogen atoms, i.e. the contribution of hydrogen atoms to a crystal's structure factor, has been developed. Crystals of L-glutamic acid were dispersed in a D-polystyrene matrix containing 4-methacryloyloxy-2,2,6,6,-tetramethyl-1-piperidinyloxy to polarize their proton spins dynamically. The intensities of the diffraction peaks of the sample changed according to the proton polarization, and the structure factor of the hydrogen atoms was extracted from the proton-polarization-dependent intensities. This technique is expected to enable analyses of the structures of hydrogen-containing materials that are difficult to determine with conventional powder diffractometry.

Neutron diffraction study of superconducting [formula omitted

We have studied structural properties of La3Ni2B2N3−δ samples with distinctly different values of the superconducting transition temperature by means of powder neutron diffractometry and specific heat measurements. The refinement of lattice site occupations reveals full occupations for all sites in the La3Ni2B112N3 structure with space group I4/mmm except for nitrogen site N(2). For samples with Tc = 13.0 K and 13.7 K we obtain for the N(2) site distinctly different occupation factors of 0.90 and 0.93, respectively. The latter confirms a direct relation between the nitrogen stoichiometry and the superconducting transition temperature. Based on the analysis of temperature dependent lattice parameters, atomic displacement factors, lattice heat capacity data and ab initio phonon density of states calculations we discuss the thermal expansion and vibrational properties of superconducting La3Ni2B2N3−δ.

Collinear antiferromagnetic structure in R2Ni2In (R = Er, Tm)

R2Ni2In (R = Er, Tm) which crystalizes in the orthorhombic structure of the Mn2AlB2-type was investigated by powder neutron diffractometry. At low temperatures the rare earth magnetic moments form an antiferromagnetic structure related to the propagation vector k→=[12,0,12]. The magnetic moments are parallel to the b-axis and equal to 7.71(7) μB and 5.76(4) μB for Er and Tm, respectively. In order to verify validity of obtained magnetic structure model a symmetry analysis was performed.

Thermal evolution of exchange interactions in lightly doped barium hexaferrites

The lightly doped BaFe12−xDxO19 (D=Al3+, In3+; x=0.1 and 0.3) polycrystalline hexaferrite samples have been investigated by powder neutron diffractometry as well as by vibration sample magnetometry in a wide temperature range from 4K up to 740K and in magnetic field up to 14T to establish the nature of Fe3+(Al3+, In3+) – O2- - Fe3+(Al3+, In3+) indirect exchange interactions. The crystal structure features such as the ionic coordinates and lattice parameters have been defined and Rietveld refined. The Invar effect has been observed in low temperature range below 150K. It was explained by the thermal oscillation anharmonicity of ions. It is established that the ferrimagnet-paramagnet phase transition is a standard second-order one. From the macroscopic magnetization measurement the Curie temperature and ordered magnetic moment per nominal iron ion are obtained. From the microscopic diffraction measurement the magnetic moments at all the nonequivalent ionic positions and total magnetic moment per iron ion have been obtained at different temperatures down to 4K. The light diamagnetic doping mechanism and magnetic structure model are proposed. The effect of light diamagnetic doping on nature of Fe3+(Al3+, In3+) – O2- - Fe3+(Al3+, In3+) indirect exchange interactions with temperature increase is discussed.

Structure and magnetic properties of BaFe11.9In0.1O19 hexaferrite in a wide temperature range

The investigations of the crystal and magnetic structure by powder neutron diffractometry as well as the magnetic properties by vibration sample magnetometry for the BaFe11.9In0.1O19 polycrystalline sample have been performed in a wide temperature range from 10 K up to 730 K and in the magnetic fields up to 14 T. The atomic coordinates and lattice parameters have been Rietveld refined. The Invar effect has been observed in low temperature range below 150 K. The temperature evaluation of the main FeO bond lengths and FeO Fe bond angles are constructed. The increase of microstress value with decreasing temperature has been defined from Rietveld refinement. From the microscopic diffraction measurement the magnetic moments at different atomic position and total magnetic moment per iron ion have been defined at different temperatures. The nature of the intrasublattice and intersublattice Fe3+O2−Fe3+ indirect exchange interactions is investigated at the different temperatures. From the macroscopic magnetization measurement the Curie temperature and the ordered magnetic moment per nominal iron ion are obtained. It is established that the ferrimagnet-paramagnet phase transition is a standard second-order one. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

Magnetic Ordering in BaFe $$_{11.9}$$ 11.9 In $$_{0.1}$$ 0.1 O $$_{19}$$ 19 Hexaferrite

The crystal and magnetic structure by powder neutron diffractometry as well as the magnetic properties by vibration sample magnetometry for the BaFe $$_{11.9}$$ In $$_{0.1}$$ O $$_{19}$$ polycrystalline sample have been performed in a wide temperature range from 10 up to 730 K and in magnetic field up to 14 T. The atomic coordinates and lattice parameters have been Rietveld refined. The Invar effect has been observed in the low-temperature range below 150 K. It was explained by the thermal oscillation anharmonicity of atoms. The increase of the microstress value with decreasing temperature has been defined from Rietveld refinement. It is established that the ferrimagnet–paramagnet phase transition is a standard second-order one. From the macroscopic magnetization measurement, the Curie temperature and ordered magnetic moment per nominal iron ion are obtained. From the microscopic diffraction measurement, the magnetic moments at different atomic position and total magnetic moment per iron ion have been defined at different temperatures. The most likely reasons and the mechanism of magnetic ordering are discussed.

Crystal structure and magnetic properties of the BaFe12−xInxO19 (x=0.1–1.2) solid solutions

The investigations of the crystal and magnetic structure by powder neutron diffractometry as well as the magnetic properties by vibration sample magnetometry for the BaFe12−xInxO19 (x=0.1–1.2) solid solutions have been performed at different temperatures and magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The Invar effect has been observed in low temperature range (from 150K to 10K). It was explained by the thermal oscillation anharmonicity of atoms. The increase of microstress value with decreasing temperature has been defined from Rietveld refinement. The Curie temperature and change of total magnetic moment per formula unit have been defined for all the compositions of the barium hexaferrites BaFe12−xInxO19 (x=0.1–1.2) solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

Evolution of structure and physical properties in Al-substituted Ba-hexaferrites**Project supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISiS” (Grant No. K4-2015-040). L. Panina acknowledges support under the Russian Federation State contract for organizing a scientific work.

The investigations of the crystal and magnetic structures of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range (from 4.2 K to 150 K). It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

Synthesis and transport properties of ternary type-I Si clathrate K8Al7Si39

A ternary type-I Si clathrate, K8AlxSi46−x, which is a candidate functional material composed of abundant non-toxic elements, was synthesized and its transport properties were investigated at temperatures ranging from 10 to 320 K. The synthesized compound is confirmed to be the ternary type-I Si clathrate K8Al7Si39 with a lattice parameter of a = 10.442 Å using neutron powder diffractometry and inductively coupled plasma optical emission spectrometry. Electrical resistivity and Hall coefficient measurements revealed that K8Al7Si39 is a metal with electrons as the dominant carriers at a density of approximately 1 × 1027/m3. The value of Seebeck coefficient for K8Al7Si39 is negative and its absolute value increases with the temperature. The temperature dependence of the thermal conductivity is similar to that for a crystalline solid. The dimensionless figure of merit is approximately 0.01 at 300 K, which is comparable to that for other ternary Si clathrates.

Crystal structure and magnetic properties of the BaFe12−xAlxO19 (x=0.1–1.2) solid solutions

The investigations of the crystal and magnetic structure by powder neutron diffractometry as well as the magnetic properties by vibration sample magnetometry for the BaFe12−xAlxO19 (x=0.1–1.2) solid solutions have been performed at different temperatures and magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The Invar effect has been observed in low temperature range (from 150 to 4.2K). It was explained by the thermal oscillation anharmonicity of atoms. The increase of microstress value with decreasing temperature has been defined from Rietveld refinement. The Curie temperature and change of total magnetic moment per formula unit have been defined for all the compositions of the barium hexaferrites BaFe12−xAlxO19 (x=0.1–1.2) solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

Lithium Diffusion Pathways in 3R-LixTiS2: A Combined Neutron Diffraction and Computational Study

Layered lithium transition-metal sulfides have long been discussed as early electrode materials for lithium-ion batteries. However, fundamental knowledge of lithium-ion migration in these solids is still lacking. In this study, we report on the diffusion dynamics in lithium-deficient high-temperature polymorphs of lithium titanium sulfides (3R-LixTiS2; x = 0.7, 0.9) as analyzed using powder neutron diffractometry and density functional theory (DFT) climbing-image nudged-elastic-band (cNEB) calculations. Two classes of probable migration pathways have been identified from the scattering-length density distributions (filtered using the maximum-entropy method [MEM]) and the probability density functions (PDFs, modeled from anharmonic Debye–Waller factors): direct diffusion in the (001) plane as the major mechanism and indirect diffusion through adjacent tetrahedral voids as a minor mechanism. Calculated activation barriers agree well with one-particle potentials (OPPs) derived from measurements for Li0.7TiS2 (0.484[14] and 0.88[4] eV) but deviate for Li0.9TiS2. The discrepancy at low defect concentration is attributed to the failure of the OPP derivation and the different nature of the methods (space-time averaged vs individual-ion perspective). This work elucidates the pathways of lithium-ion diffusion in 3R-LixTiS2 and points out pitfalls in established experimental/computational methods.

The High-Temperature Transformation from 1T- to 3R-Li x TiS2 (x = 0.7, 0.9) as Observed in situ with Neutron Powder Diffraction

Abstract Layered titanium disulfide is used as lithium-ion intercalating electrode material in batteries. The room-temperature stable trigonal 1T polymorphs of the intercalates Li x TiS2(x ≤ 1) are widely-investigated. However, the rombohedral 3R polymorphs, being stable at higher temperatures for large x, are less well known. In this study, we report on the synthesis of phase-pure 1T-Li x TiS2(x = 0.7, 0.9) and its transformation to the 3R phase between 673 and 873 K as monitored using high-temperature neutron powder diffractometry. For the 3R polymorph, full Rietveld refinements show lithium ions to be statistically distributed over octahedral voids at the fractional coordinates 0, 0, 1/2 , exclusively. The comparison of Madelung energies with results of periodic quantum-chemical calculations reveals that the evolution of lattice parameters and the room-temperature stability of the 1T phase are not governed by electrostatics, but by correlation and polarization. The insights gained do not only elucidate the structure of 3R-Li x TiS2, but also help to understand and control polymorphism in layered transition-metal sulfides.

Crystal Structure, Oxygen Deficiency, and Oxygen Diffusion Path of Perovskite-Type Lanthanum Cobaltites La0.4Ba0.6CoO3−δ and La0.6Sr0.4CoO3−δ

Crystal structures of perovskite-type lanthanum cobaltites, La0.4Ba0.6CoO3−δ and La0.6Sr0.4CoO3−δ, have been studied by in situ neutron powder diffractometry from 27 to 1258 °C. La0.4Ba0.6CoO3−δ has a cubic Pm3̅m structure in the whole temperature range, while La0.6Sr0.4CoO3−δ exhibits a phase transition from hexagonal (R3̅c) to cubic (Pm3̅m) symmetry between 400 and 600 °C. Geometric information on oxygen diffusion is essential to understand the facile electrode reaction of perovskite-type cobaltites, but previous approaches have been limited to computational predictions. Here we provide long-awaited experimental evidence for a curved three-dimensional oxygen diffusion path in an ABO3 mixed ionic-electronic conductor, La0.4Ba0.6CoO3−δ. The oxide ions diffuse in the ⟨100⟩ direction near the stable position, while the path is along ⟨110⟩ around the middle point of the path. The connected path was not visualized in La0.6Sr0.4CoO3−δ but in La0.4Ba0.6CoO3−δ, which indicates the higher oxygen diffusivity in La0.4Ba0.6CoO3−δ. The oxygen defect concentration, bottleneck size for oxygen diffusion, and oxygen atomic displacement parameter of La0.4Ba0.6CoO3−δ are higher than those of La0.6Sr0.4CoO3−δ, which are responsible for the higher oxygen diffusivity in La0.4Ba0.6CoO3−δ.

Structural and Magnetic Properties of Dilute Spinel Ferrites: Neutron Diffractometry and Magnetometry Investigations

Magnetic properties of highly zinc-substituted manganese ferrites are discussed on the basis of cation distribution. High throughput neutron powder diffractometry indicates that the prepared samples possess a nearly normal spinel structure, where the substitution of nonmagnetic zinc ions mainly causes the dilution of magnetic ions in the A-sublattice and consequently affects bond-randomness in the B-sublattice. On the other hand, the estimated occupancy of manganese ions in the B site indicates that random anisotropy effects due to local Jahn-Teller distortions gradually weaken with the substitution. Bulk magnetometry indicates that the substitution smears the transition from a paramagnetic phase to a soft-magnetic phase. Furthermore, at lower temperatures, such a soft-magnetic phase is destabilized and a magnetic glassy state appears. These features of the magnetic properties of dilute spinel ferrites are discussed from the viewpoint of the above-mentioned various types of disorders.

Structural and thermoelastic properties of CaTiO 3 perovskite between 7 K and 400 K

The structural and thermoelastic properties of CaTiO 3 perovskite have been studied using high-resolution powder neutron diffractometry at eighty temperatures in the range 7–400 K. The temperature variation of the unit cell volume, the thermodynamic Grüneisen parameter and the isobaric heat capacity are analysed using a two-term Debye model. Structural parameters are presented as the magnitudes of symmetry-adapted basis-vectors of seven normal modes with wavevectors that lie on the surface of the Brillouin zone of the primitive cubic aristotype phase, and a structural basis for the temperature-dependence of the bond lengths is proposed. A consistency between the vibrational Debye temperatures derived from the atomic displacement parameters and the mean values of the vibrational energies of the three atomic species calculated from the partial phonon densities of states has been found.

放射光および中性子粉末回折によるBa2NdSn0.6Sb0.4O6-δの結晶構造解析

放射光および中性子粉末回折によるBa2NdSn0.6Sb0.4O6-δの結晶構造解析

ChemInform Abstract: A Novel Boroncarbide, Y2B3C2 - X-Ray Single Crystal and Neutron Powder Diffraction Analysis.

The crystal structure of Y2B3C2 was analysed by means of room temperature X-ray single crystal and neutron powder diffractometry. Y2B3C2 crystallises with the Gd2B3C2-type (space group: Cmmm - No. 65, Z=2). The unit cell dimensions are: a=0.3405(5), b=1.3765(6), c=0.3631(6) nm, b/a=4.044, V=0.1702 nm3 the X-ray density is: ρx=4.57 Mgm−3. The structure was solved by combined Patterson-Difference Fourier methods. Residual values are: RF=ΣΔF/ΣFo=0.027, Rw=0.020, for an asymmetric set of 232 independent reflections (Fo>3σ(Fo)). Boron atoms B1, each in triangular metal co-ordination, form infinite zigzag chains (dB1–B1=0.1923 nm) branched with carbon atoms. Bond angles in the chain are ϕB1–B1–B1=124.6°. Carbon atoms are at a distance of dB1–C=0.1552 in rectangular co-ordination of four metal atoms. The branched boron chains are connected by a bridging boron atom B2 linking the carbon atoms in form of a linear bridge at dC–B2=0.1442 nm. Rietveld refinement of the neutron powder data from Y2B3C2(11B–isotope) confirms the nuclear structure arrangement as well as the full occupancy of all the non-metal atom sites.

(Applications 6)Crystal Structure Analysis of Catalysts by Neutron Powder Diffractometry

中性子粉末回折法による，無機触媒の結晶構造と核密度分布の解析，生成相と相転移の研究を概説した。酸窒化物光触媒のN原子席におけるO原子の占有率を精密化することができる。セリアージルコニア排ガス触媒の結晶構造，相転移及び核密度分布が，中性子回折法により調べられた。原子変位パラメーターと核密度分布から，酸素イオンの拡散及び触媒活性を考察することができる。ペロブスカイト型及び関連酸化物の結晶構造と酸素イオンの拡散経路を研究するのに中性子回折法が利用された。

Low temperature magnetic order in HoFe 2Ge 2

HoFe 2Ge 2 crystallizes in the tetragonal ThCr 2Si 2-type crystal structure. The polycrystalline sample of the compound has been investigated by electrical resistivity measurement (down to 0.4 K) and powder neutron diffractometry (down to 0.90 K). The temperature dependence of the electrical resistivity shows an anomaly close to 1.6 K. The neutron diffraction reveals the presence of an incommensurate antiferromagnetic order described by the propagation vector k → = [ 0.1604 ( 7 ) , 0.1604 ( 7 ) , 0.448 ( 5 ) ] below 1.6 K. The magnetic moments are aligned along the c -axis.