Inelastic Neutron Scattering Study Research Articles

Effects of cage topology on ethylene adsorption mechanism in silver exchanged CHA and RHO zeolites: An Inelastic Neutron Scattering and Density Functional study

Zeolite-based adsorbents have been successfully used for many challenging separations due to their tunable properties. A particularly notable application involves the separation of light olefins from paraffins, wherein the molecular sieving properties of zeolites play a pivotal role. Additionally, the selective interaction of alkenes with transition metal cations, positioned within the channels and cavities of microporous zeolites, further enhances separation capabilities.This study aims to comprehensively characterize the interactions between ethylene and Ag+ exchanged zeolites, employing a multidisciplinary approach, combining Inelastic Neutron Scattering (INS), Infrared (IR) spectroscopy, Nuclear Magnetic Resonance (NMR), UV–Vis and Density Functional Theory (DFT) calculations. CHA and RHO, zeolites largely applied in gas separation processes, were chosen due to their similar small pore sizes and pore volume, but different cavity shapes and flexibilities.The interpretation of derived DFT Electron Density Difference, experimentally supported by 13C Solid State NMR results, provide an understanding of each framework’s role during the charge transfer mechanisms between ethylene and transition metal species. Specific deformations in the flexible framework of zeolite RHO explain a blueshift of the band at 400 cm−1 in the librational region of INS spectra compared to CHA. This structural change in RHO, represented by the conic shape of the cage 8-ring side pockets, increases steric effects over the adsorbate while rendering the metallic adsorption center less exposed within the zeolite’s cavity, finally leading to a weaker adsorption energy. The redshift of C=C stretching frequencies observed by IR spectroscopy and DFT calculations, as well as C=C and C-H bond lengthening of ethylene confirm the formation of π-complexes on silver in both zeolites and allowed a further evaluation of the effects of the different frameworks cages on the aforementioned interaction.

Inelastic Neutron Scattering Study of Phonon Density of States of Iodine Oxides and First-Principles Calculations.

Iodine oxides I2Oy (y = 4, 5, 6) crystallize into atypical structures that fall between molecular- and framework-base types and exhibit high reactivity in an ambient environment, a property highly desired in the so-called "agent defeat materials". Inelastic neutron scattering experiments were performed to determine the phonon density of states of the newly synthesized I2O5 and I2O6 samples. First-principles calculations were carried out for I2O4, I2O5, and I2O6 to predict their thermodynamic properties and phonon density of states. Comparison of the INS data with the Raman and infrared measurements as well as the first-principles calculations sheds light on their distinctive, anisotropic thermomechanical properties.

Revealing the effect of interstitial oxygen on the low-energy crystal electric field excitations of Pr3+ in 214 -nickelates

We report an inelastic neutron scattering study (INS) on the low-energy crystal electric field (CEF) excitations of ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{NiO}}_{4+\ensuremath{\delta}}$ single crystals at various temperatures. The observed low-$E$ CEF level of the O-doped sample $(x=0,\phantom{\rule{4pt}{0ex}}\ensuremath{\delta}\ensuremath{\approx}0.24)$ at $\ensuremath{\sim}5.5\phantom{\rule{4pt}{0ex}}\mathrm{meV}$ appears at significantly lower energy than that of the Sr-doped sample $(x=0.5,\phantom{\rule{4pt}{0ex}}\ensuremath{\delta}=0.0)$ at $\ensuremath{\sim}8.5\phantom{\rule{4pt}{0ex}}\mathrm{meV}$. Applying the point charge (PC) model calculation, this has been interpreted as an effect of the interstitial oxygen via lowering the local symmetry and modifying the CEF environment of the central rare earth ${\mathrm{Pr}}^{3+}$ $(^{3}H_{4})$ ions.

On the energetics of binding and hydride exchange in the RuH2(H2)2[P(C5H9)3)]2 complex as revealed by inelastic neutron scattering and DFT studies

Low temperature quantum rotation of dihydrogen in RuH2(H2)2[P(C5H9)3)]2 switched to a facile hydride exchange above 150 K.

Inelastic Neutron Scattering Study of Magnetic Exchange Pathways in MnS

Inelastic Neutron Scattering Study of Magnetic Exchange Pathways in MnS

On the Structural Transformation of Ni/BaH2 During a N2-H2 Chemical Looping Process for Ammonia Synthesis: A Joint In Situ Inelastic Neutron Scattering and First-Principles Simulation Study

The demand for decarbonizing the ammonia industry by using renewable energy has invoked increasing research interests into catalyst development for effective N2 reduction under mild conditions. Hydride-based materials are among some of the emerging catalysts for ammonia synthesis at ambient pressure and low temperatures (< 673 K). A recent chemical looping process based on Ni/BaH2 showed the most promise as it can realize ammonia production at a temperature as low as 373 K and under ambient pressure. However, the chemical transformation of the hydride catalyst at the molecular level remains unclear in this process. In this work, we report detailed in situ neutron spectroscopy and diffraction investigations along with first-principles simulations on the structural transformation of Ni/BaH2 during the nitridation and hydrogenation steps in the chemical looping process for ammonia synthesis. It was shown that a ball-milling process of the starting Ni/BaH2 could significantly decrease the size of BaH2 and increase the density of defects, thus potentially enhancing the reactivity of the hydride. The evolution from BaH2 to barium imide (BaNH) was evidenced in the inelastic neutron scattering (INS) and neutron diffraction results during the N2 reaction step. During the hydrogenation study, in addition to the recovery of BaH2, a possible intermediate species, N-deficient barium imide, was also detected. In comparing the N2 and H2 reaction steps, the neutron results indicate that the hydrogenation step appears more difficult than the nitridation step, confirming the facile N2 fixation property of Ni/BaH2 catalyst in ammonia synthesis.

Magnetic properties and crystal field splitting of the rare-earth pyrochlore Er2Ir2O7

The effects on the rare-earth crystal-field-splitting schemes of incorporation of large spin-orbit coupling ($5d$) ions, such as ${\text{Ir}}^{\text{4}}+$, into the rare-earth pyrochlores are largely unknown. We report on the preparation, specific heat, magnetization, and inelastic neutron-scattering study of ${\text{Er}}_{\text{2}}{\text{Ir}}_{\text{2}}{\text{O}}_{\text{7}}$ pyrochlore. An anomaly in specific heat and bifurcation of zero-field cooled and field cooled magnetization indicates an ordering of the Ir sublattice below 140 K, in good agreement with other rare-earth pyrochlore iridates. The Er sublattice ordering below 2 K can be considered short range as well, following the development of specific-heat and magnetization data down to low temperatures. The inelastic neutron scattering allowed us to unambiguously determine the crystal-field (CF) eigenenergies and parameters of ${\text{Er}}_{\text{2}}{\text{Ir}}_{\text{2}}{\text{O}}_{\text{7}}$, which are dictated dominantly by nearest-neighbor anions (the oxygen cage around the Er cation). The influence of the magnetic iridium cations on the erbium CF scheme is rather moderate despite the strong spin-orbit coupling expected in a $5d$ metal, which is evident when comparing the energy spectra of this iridate and other $3d$- or $4d$-metal containing erbium pyrochlores. The determined CF parameters were subsequently utilized for calculations of magnetization and specific-heat CF contributions, leading to an excellent agreement with experimental data.

Possible Mott transition in layeredSr2Mn3As2O2single crystals

Single crystals of ${\mathrm{Sr}}_{2}{\mathrm{Mn}}_{3}{\mathrm{As}}_{2}{\mathrm{O}}_{2}$ have been grown for the first time, for which we show a possible layer-selective Mott insulator behavior. This compound stands out as a hybrid structure of ${\mathrm{MnO}}_{2}$ and MnAs layers, analogously to the active ${\mathrm{CuO}}_{2}$ and FeAs layers, respectively, in the cuprate and iron-based high-temperature superconductors. Electrical transport, neutron diffraction measurements, together with density functional theory calculations on ${\mathrm{Sr}}_{2}{\mathrm{Mn}}_{3}{\mathrm{As}}_{2}{\mathrm{O}}_{2}$ single crystals converge toward a picture of independent magnetic order at ${T}_{1}\ensuremath{\sim}79$ K and ${T}_{2}\ensuremath{\sim}360$ K for the two Mn sublattices, with insulating behavior at odds with the metallic behavior predicted by calculations. Furthermore, our inelastic neutron-scattering studies of spin-wave dispersions for the Mn(1) sublattice reveal an effective magnetic exchange coupling of $SJ\ensuremath{\sim}3.7$ meV. This is much smaller than those for the Mn(2) sublattice.

Magnetic Excitations of the Classical Spin Liquid MgCr_{2}O_{4}.

We report a comprehensive inelastic neutron-scattering study of the frustrated pyrochlore antiferromagnet MgCr_{2}O_{4} in its cooperative paramagnetic regime. Theoretical modeling yields a microscopic Heisenberg model with exchange interactions up to third-nearest neighbors, which quantitatively explains all of the details of the dynamic magnetic response. Our work demonstrates that the magnetic excitations in paramagnetic MgCr_{2}O_{4} are faithfully represented in the entire Brillouin zone by a theory of magnons propagating in a highly correlated paramagnetic background. Our results also suggest that MgCr_{2}O_{4} is proximate to a spiral spin-liquid phase distinct from the Coulomb phase, which has implications for the magnetostructural phase transition in MgCr_{2}O_{4}.

Inelastic Neutron Scattering Study of the Aluminum and Brønsted Site Location in Aluminosilicate LTA Zeolites

Inelastic neutron scattering (INS) has been employed to determine the location of aluminum and Bronsted acid sites in an LTA-5 sample (Si/Al = 5) with few defects of connectivity. A large number of Al and Bronsted distributions were computationally generated, and a selection of nine distributions were found to be in agreement with the 29Si NMR spectrum of the LTA sample. From the nine subsequent periodic density functional theory calculations, one of the models shows a good agreement with the INS spectrum. The suggested distribution shows Al atoms to be homogeneously distributed in the framework and protons distributed relatively far from each other. A CIF file containing the LTA-5 distribution of Al and H matching the experiments is given as the result.

Time-of-Flight Elastic and Inelastic Neutron Scattering Studies on the Localized 4d Electron Layered Perovskite La5Mo4O16

The magnetic structure and spin-wave excitations in the quasi-square-lattice layered perovskite compound La$_5$Mo$_4$O$_{16}$ were studied by a combination of neutron diffraction and inelastic neutron scattering techniques using polycrystalline sample. Neutron powder diffraction refinement revealed that the magnetic structure is ferrimagnetic in the $ab$ plane with antiferromagnetic stacking along the $c$ axis where the magnetic propagation vector is $\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. The ordered magnetic moments are estimated to be $0.54(2)\mu_\text{B}$ for Mo$^{5+}$ ($4d^1$) ions and $1.07(3)\mu_\text{B}$ for Mo$^{4+}$ ($4d^2$) ions at 4 K, which are about half of the expected values. The inelastic neutron scattering results display strong easy-axis magnetic anisotropy along the $c$ axis due to the spin-orbit interaction in Mo ions evidenced by the spin gap at the magnetic zone center. The model Hamiltonian consisting of in-plane anisotropic exchange interactions, the interlayer exchange interaction, and easy-axis single-ion anisotropy can explain our inelastic neutron scattering data well. Strong Ising-like anisotropy and weak interlayer coupling compared with the intralayer exchange interaction can explain both the high-temperature magnetoresistance and long-time magnetization decay recently observed in La$_5$Mo$_4$O$_{16}$.

Interaction of spin-orbital-lattice degrees of freedom: Vibronic state of the corner-sharing-tetrahedral frustrated spin system HoBaFe4O7 by dynamical Jahn-Teller effect

A powder inelastic neutron-scattering study of ${\mathrm{HoBaFe}}_{4}{\mathrm{O}}_{7}$ (HBFO) revealed characteristic magnetic excitations associated with geometrical spin frustration. Dispersionless excitations in energy ($\ensuremath{\omega}$) and wave-vector ($Q$) space are observed at several discrete energies. Some of them can be attributed to crystal-field excitations of ${\mathrm{Ho}}^{3+}$ in octahedral symmetry, but the others are explained instead by the vibronic state of the ${\mathrm{Fe}}^{2+}$ dynamical Jahn-Teller effect with orbit-spin coupling, indicating interaction among the spin, the orbital, and the lattice degree of freedom. The antiferromagnetic HBFO lattice has cubic symmetry, and both ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ reside on corner-sharing tetrahedra with a number ratio of 3:1. Even though ${\mathrm{Fe}}^{2+}$ is a Jahn-Teller active ion in tetrahedral symmetry, the system does not exhibit any static lattice distortion to the lowest temperature studied (4 K). The observed excitations can be understood by considering the dynamical interaction among spin-orbital-lattice degrees of freedom, indicating that spin fluctuation due to the frustration effect induces the dynamical Jahn-Teller effect, although in most cases a Jahn-Teller active ion ${\mathrm{Fe}}^{2+}$ takes the static Jahn-Teller effect in a magnetic oxide system.

Inelastic Neutron Scattering Study on the Location of Brønsted Acid Sites in High Silica LTA Zeolite

The presence of Bronsted acid sites (SiOHAl) is crucial in many of the applications of zeolites in petroleum refining and related industries. This acidity relies on the number and location of acid sites, but the latter is difficult to know accurately in spite of a large number of experimental techniques available. Zeolites usually contain many types of acid sites depending on the crystallographic different O-sites and their chemical environment. In the present work we show how inelastic neutron scattering (INS) can be employed for an accurate determination of the location of Bronsted acid sites in zeolites. This is achieved using a sample of LTA zeolite with few defects of connectivity, few (O1H, O2H, O3H) crystallographically different oxygens, and high Si/Al ratio. The narrow and intense peaks corresponding to SiOH bending modes ca. 1100 cm–1 have been shown, using periodic DFT calculations, to strongly depend on the type of oxygen to which the proton is bonded. A comparison between calculations and INS...

Inelastic Neutron Scattering and Theoretical Studies of H2 Sorption in a Dy(III)-Based Phosphine Coordination Material

A combined inelastic neutron scattering (INS) and theoretical study of H2 sorption was performed in PCM-16, a phosphine coordination material (PCM) with the empirical formula [(CH3)2NH2][Dy2(tctpo)2(O2CH)] (tctpo = tris(p-carboxylato)triphenylphosphine oxide). INS measurements at different loadings of H2 revealed a peak occurring at low rotational tunnelling energies (ca. 5–8 meV), which corresponds to a high barrier to rotation and, therefore, a strong interaction with the host. Molecular simulations of H2 sorption in PCM-16 revealed that the H2 molecules sorbed at two main sites in the material: (1) the (CH3)2NH2+ counterions and (2) within the small pores of the framework. Two-dimensional quantum rotation calculations revealed that the peak occurring from approximately 5–8 meV in the INS spectra for PCM-16 is associated with sorption onto the (CH3)2NH2+ ions. These counterions provide for the strongest H2 sorption sites in the material, which corresponds to an isosteric heat of adsorption (Qst) value of close to 8 kJ mol–1. The calculated rotational barrier for the (CH3)2NH2+–H2 interaction in PCM-16 (45.60 meV) is higher than those for a number of extant metal–organic frameworks (MOFs), especially those that contain open-metal sites. This study provides insights into the H2 sorption mechanism in a PCM for the first time and shows how the inclusion of counterions in porous materials is a promising method to increase the H2 sorption energetics in such materials.

Magnetic Transitions in Iron Porphyrin Halides by Inelastic Neutron Scattering and Ab Initio Studies of Zero-Field Splittings.

Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H₂TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm⁻¹ for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm⁻¹, E = 0.1(2) cm⁻¹ and D = 13.4(6) cm⁻¹, E = 0.3(6) cm⁻¹ for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm⁻¹ for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X = F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the ⁶A₁ ground state. D was calculated from wave functions of the electronic multiplets spanned by the d⁵ configuration of Fe(III) along with spin–orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX₆³⁻ complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies e(λ)(X) (λ = σ, π) in the series from X = F to I. Analysis of this correlation using second-order perturbation theory expressions in terms of angular overlap parameters rationalizes the experimentally deduced trend. D parameters from CASSCF and NEVPT2 results have been calibrated against those from the INS data, yielding a predictive power of these approaches. Methods to improve the quantitative agreement between ab initio calculated and experimental D and spectroscopic transitions for high-spin Fe(III) complexes are proposed.

Probing the effects of 2D confinement on hydrogen dynamics in water and ice adsorbed in graphene oxide sponges.

We studied the single particle dynamics of water and ice adsorbed in graphene oxide (GO) sponges at T = 293 K and T = 20 K. We used Deep Inelastic Neutron Scattering (DINS) at the ISIS neutron and muon spallation source to derive the hydrogen mean kinetic energy, 〈EK〉, and momentum distribution, n(p). The goal of this work was to study the hydrogen dynamics under 2D confinement and the potential energy surface, fingerprinting the hydrogen interaction with the layered structure of the GO sponge. The observed scattering is interpreted within the framework of the impulse approximation. Samples of both water and ice adsorbed in GO show n(p) functions with almost harmonic and anisotropic line shapes and 〈EK〉 values in excess of the values found at the corresponding temperatures in the bulk. The hydrogen dynamics are discussed in the context of the interaction between the interfacial water and ice and the confining hydrophilic surface of the GO sponge.

IV ソフトマター・生体物質の非弾性・準弾性中性子散乱研究

ソフトマター・生体物質が持つ特性について記載し，その研究における非弾性・準弾性中性子散乱の特徴を述べた。現状の研究状況を明らかにするため非弾性・準弾性中性子散乱研究の歴史を手短にまとめ，ソフトマターのスローダイナミクスの研究例として，中性子スピンエコー法による高分子ミセルの呼吸モードと高分子ゲルの静的及び動的揺らぎの研究について解説した。

Inelastic Neutron Scattering Studies of Methyl Chloride Synthesis over Alumina

Not only is alumina the most widely used catalyst support material in the world, it is also an important catalyst in its own right. One major chemical process that uses alumina in this respect is the industrial production of methyl chloride. This is a large scale process (650,000 metric tons in 2010 in the United States), and a key feedstock in the production of silicones that are widely used as household sealants. In this Account, we show how, in partnership with conventional spectroscopic and reaction testing methods, inelastic neutron scattering (INS) spectroscopy can provide additional insight into the active sites present on the catalyst, as well as the intermediates present on the catalyst surface. INS spectroscopy is a form of vibrational spectroscopy, where the spectral features are dominated by modes involving hydrogen. Because of this, most materials including alumina are largely transparent to neutrons. Advantageously, in this technique, the entire "mid-infrared", 0-4000 cm(-1), range is accessible; there is no cut-off at ~1400 cm(-1) as in infrared spectroscopy. It is also straightforward to distinguish fundamental modes from overtones and combinations. A key parameter in the catalyst's activity is the surface acidity. In infrared spectroscopy of adsorbed pyridine, the shifts in the ring stretching modes are dependent on the strength of the acid site. However, there is a very limited spectral range available. We discuss how we can observe the low energy ring deformation modes of adsorbed pyridine by INS spectroscopy. These modes can undergo shifts that are as large as those seen with infrared inspectroscopy, potentially enabling finer discrimination between acid sites. Surface hydroxyls play a key role in alumina catalysis, but in infrared spectroscopy, the presence of electrical anharmonicity complicates the interpretation of the O-H stretch region. In addition, the deformations lie below the infrared cut-off. Both of these limitations are irrelevant to INS spectroscopy, and all the modes are readily observable. When we add HCl to the catalyst surface, the acid causes changes in the spectra. We can then deduce both that the surface chlorination leads to enhanced Lewis acidity and that the hydroxyl group must be threefold coordinated. When we react η-alumina with methanol, the catalyst forms a chemisorbed methoxy species. Infrared spectroscopy clearly shows its presence but also indicates the possible coexistence of a second species. Because of INS spectroscopy's ability to discriminate between fundamental modes and combinations, we were able to unambiguously show that there is a single intermediate present on the surface of the active catalyst. This work represents a clear example where an understanding of the chemistry at the molecular level can help rationalize improvements in a large scale industrial process with both financial and environmental benefits.

Inelastic Neutron Scattering (INS) Study of Low Frequency Vibrations and Hydrogen Bonding of (E)-Benzil Monoxime

Abstract (E)-benzil monoxime (or (E)-monoxime of 1,2 diphenyloetandion), which is the subject of this paper, belongs to the family of bioactive organic substances. Many of them have been investigated for many years by inelastic, incoherent neutron scattering spectroscopy (IINS) but the investigation of (E)-benzil monoxime is absent from literature. Therefore (E)-benzil monoxime has been investigated using infrared, and IINS spectroscopy. Dimers of (E)-benzil monoxime were considered using B3LYP functional (connection of Becke and Lee–Yang–Parr functionals) combined with the 6-311++G(d,p) basis set method of quantum chemistry in order to improve the results obtained for a single molecule. In (E)-benzil monoxime, extra bands corresponding primarily to hydrogen bond vibrations (γ bending out of plane of hydrogen bond at 312.3, 372, 470.5, 578.3, 703.5, 748.7, 780.4 cm –1, σ stretching of hydrogen bond bridge at 124.3, 140.9, 176.5, 190.1, 223.6, 259.1, 290.5, 501.8, 623.5 cm –1, δ bending in plane of hydrogen bond at 1102.4, 1371,1452,1535, 1630.6 cm –1, λ bending of hydrogen bond bridge at ca. 40 cm –1, ν stretching band OH at 3397 cm –1) have been identified. Some of them could be discovered only by using IINS method and this is the main result of this work. Additionally we'd like to compare the structure of the compound and the structure of oximes previously investigated by us . Taking into account the structure and IINS results for three oximes investigated by us, we can estimate the difference of hydrogen bond power in those three oximes. Hence the power of hydrogen bond in the (E)-benzil monoxime seems to be the smallest in the group of the three compounds: (E)-benzil monoxime, (E)-2-hydroxyimino-2-cyanoacetic acid ethyl ester (2-oxime), acid K salt of 2-oxime.

High-temperature high pressure cell for neutron-scattering studies

In this study, a simple high-temperature high pressure cell concept has been developed to enable neutron diffraction and quasi-elastic and inelastic neutron-scattering studies to be conducted on large-volume powder samples of ceramic proton conductors at pressures of up to 1 GPa and at temperatures of up to 770 K. Details of the cell are provided, along with the first experimental neutron diffractograms (at 0.62 GPa and 300 K), quasi-elastic neutron-scattering spectra (at 0.58 GPa and 770 K) and inelastic neutron spectra (at 0.75 GPa and 530 K) determined for samples of BaCe0.8Y0.2O3.