Dynamics of Na Ion in the Amorphous Na2Si2O5 Using Quasielastic Neutron Scattering and Molecular Dynamics Simulations
Mayanak K. Gupta, Sanjay K. Mishra, Ranjan Mittal, Baltej Singh, Prabhatasree Goel, Sanghamitra Mukhopadhyay, Rakesh Shukla, Srungarpu N. Achary, Avesh K. Tyagi, Samrath L. Chaplot
We have investigated the dynamics of Na ions in amorphous Na2Si2O5, a potential solid electrolyte material for Na-battery. We have employed quasielastic neutron scattering (QENS) technique in the amorphous Na2Si2O5 from 300 to 748 K to understand the diffusion pathways and relaxation timescales of Na atom dynamics. The microscopic analysis of the QENS data has been performed using ab-initio and classical molecular dynamics simulations (MD) to understand the Na-ion diffusion in the amorphous phase. Our experimental studies show that the traditional model, such as the Hall and Ross (H-R) model, fairly well describe the diffusion in the amorphous phase giving a mean jump length of ~3 Å and residence time about 9.1 picoseconds. Our MD simulations have indicated that the diffusion of Na+ ions occurs in the amorphous phase of Na2Si2O5 while that is not observed in the crystalline orthorhombic phase even up to 1100 K. The MD simulations have revealed that in the amorphous phase, due to different orientations of silicon polyhedral units, accessible pathways are opened up for Na+ diffusions. These pathways are not available in the crystalline phase of Na2Si2O5 due to rigid spatial arrangement of silicon polyhedral units.
We previously derived a theorem about the {\em coherent} quasielastic neutron-scattering signal from a $d$-dimensional lattice of $N$ molecules that are undergoing rotational jump diffusion (around an $n$-fold axis), assuming that there are no correlations between the molecules. In the present paper molecular correlations are treated, but only in the sense that several molecules could reorient simultaneously as in a cog-wheel mechanism. Moreover, we do not examine the possibility that the relaxation times of these combined reorientations could depend on details of the local environment created…
We have performed quasielastic neutron scattering (QENS) experiments up to 1243 K and ab-initio molecular dynamics (AIMD) simulations to investigate the Na diffusion in various phases of NaAlSiO4 (NASO), namely, low-carnegieite (L-NASO; trigonal), high-carnegieite (H-NASO; cubic) and nepheline (N-NASO; hexagonal) phases. The QENS measurements reveal Na ions localized diffusion behavior in L-NASO and N-NASO, but long-range diffusion behavior in H-NASO. The AIMD simulation supplemented the QENS measurements and showed that excess Na ions in H-NASO enhance the host network flexibility and activat…
Proton motions in hydrated proton conducting perovskites BaZr_{0.90}A_{0.10}O_{2.95} (A = Y and Sc) have been investigated using quasielastic neutron scattering. The results reveal a localized motion on the ps time scale and with an activation energy of ~10-30 meV, in both materials. The temperature dependence of the total mean square displacement of the protons suggests an onset of this motion at a temperature of about 300 K. Comparison of the QENS results to density functional theory calculations suggests that for both materials this motion can be ascribed to intra-octahedral proton transfer…
We present the investigations on atomic dynamics and Li+ diffusion in crystalline and amorphous Li2Si2O5 using quasielastic (QENS) and inelastic neutron scattering (INS) studies supplemented by ab-initio molecular dynamics simulations (AIMD). The QENS measurements in the amorphous phase of Li2Si2O5 show a narrow temperature window (700 < T < 775 K), exhibiting significant quasielastic broadening corresponding to the fast Li+ diffusion and relaxation of SiO4 units to the crystalline phase. Our INS measurements clearly show the presence of large phonon density of states (PDOS) at low energy (low…
Quasielastic neutron scattering (QENS) measurements combined with first principles based moleculardynamics calculations were conducted to study the dynamics of Li$^+$ ions in a solid-state electrolyte La$_{2/3-x}$Li$_{3x}$TiO$_{3}$ (LLTO) with $x=0.13$. By using a large $^7$Li-enriched single crystal sample, a QENS signal was clearly observed along the three principal axes [110], [111], and [001] at a temperature ($T$) of 600 K. Wave vector dependence of the linewidth of the QENS signal along each direction was explained well using the Chudley-Elliot model for jumps between the A sites of the …
In this letter we report a direct observation of a magnetic proximity effect in an amorphous thin film exchange-spring magnet by the use of neutron reflectometry. The exchange-spring magnet is a trilayer consisting of two ferromagnetic layers with high $T_c$'s separated by a ferromagnetic layer, which is engineered to have a significantly lower $T_c$ than the embedding layers. This enables us to measure magnetization depth profiles at which the low $T_c$ material is in a ferromagnetic or paramagnetic state, while the embedding layers are ferromagnetic. A clear proximity effect is observed 7 K …
Kinetics of crystallization of two amorphous alloys, Fe70Cr10B20 and Fe80Zr10B10, have been followed up by neutron thermodiffractometry experiments performed in the two axis diffractometer D20 (ILL, Grenoble). The structural changes are directly correlated with the temperature dependence of the magnetization. Fe70Cr10B20 crystallizes following a two-step process: an eutectic crystallization of alfa-Fe (bcc) and the metastable tetragonal phase (Fe0.8Cr0.2)3B followed by another eutectic transformation to the stable phase (Fe0.75Cr0.25)2B and more segregation of alfa-Fe. These tetragonal phases …
Simultaneous measurement of self-diffusion of iron and nitrogen in amorphous iron nitride (Fe86N14) using secondary ion mass spectroscopy (SIMS) technique has been done. In addition neutron reflectivity (NR) technique was employed to study the Fe diffusion in the same compound. The broadening of a tracer layer of 57Fe8615N14 sandwiched between Fe86N14 layers was observed after isothermal vacuum annealing of the films at different temperatures in SIMS measurements. And a decay of the Bragg peak intensity after isothermal annealing was observed in [Fe86N14/57Fe86N14]10 multilayers in NR. Strong …
Neutron scattering experiments have been performed on the ternary rare-earth diborocarbide Ce$^{11}$B$_2$C$_2$. The powder diffraction experiment confirms formation of a long-range magnetic order at $T_{\rm N} = 7.3$ K, where a sinusoidally modulated structure is realized with the modulation vector ${\bm q} = [0.167(3), 0.167(3), 0.114(3)]$. Inelastic excitation spectra in the paramagnetic phase comprise significantly broad quasielastic and inelastic peaks centered at $\hbar ω\approx 0, 8$ and 65 meV. Crystalline-electric-field (CEF) analysis satisfactorily reproduces the observed spectra, con…
Lead-halide organic-inorganic perovskites consist of an inorganic host framework with an organic molecule occupying the interstitial space. The structure and dynamics of these materials have been heavily studied recently due to interest in their exceptional photovoltaic properties. We combine inelastic neutron scattering, Raman spectroscopy, and quasielastic neutron scattering to study the temperature dependent dynamics of the molecular cation in CH3NH3PbBr3. By applying high resolution quasielastic neutron scattering, we confirm the [CH3NH3]+ ions are static in the low temperature orthorhombi…
An algorithm is developed for structure identification of amorphous carbonaceous nanomaterials with a joint x-ray and neutron diffraction data analysis, using the data on the chemical composition of the sample from other diagnostics. The algorithm is an extension of one formerly developed for the x-ray diffraction diagnostics of similar nanomaterials ([1] Chem. Phys. Lett., 506, 265-268 (2011)). The algorithm is tested on the example of processing the computed data for a sample which models a fragment of hydrocarbon films analyzed in [1]. The algorithm is of interest for structure diagnostics …
The low-energy part of vibration spectrum in PbMg$_{1/3}$Nb$_{2/3}$O$_3$ relaxor ferroelectric was studied by inelastic neutron scattering. We observed the coexistence of a resolution-limited central peak with strong quasielastic scattering. The line-width of the quasielastic component follows a $Γ_0+Dq^2$ dependence. We find that $Γ_0$ is temperature-dependent. The relaxation time follows the Arrhenius law well. The presence of a relaxation mode associated with quasi-elastic scattering in PMN indicates that order-disorder behaviour plays an important rôle in the dynamics of diffuse phase tran…
Spin correlations and fluctuations in the 3d-transition-metal-based icosahedral quasicrystal Zn-Fe-Sc have been investigated by neutron scattering using polycrystalline samples. Magnetic diffuse scattering has been observed in the elastic experiment at low temperatures, indicating development of static short-range-spin correlations. In addition, the inelastic scattering experiment detects a $Q$-independent quasielastic signal ascribed to single-site relaxational spin fluctuations. Above the macroscopic freezing temperature $T_{\rm f} \simeq 7$ K, the spin relaxation rate shows Arrhenius-type b…
Dynamical disorder in negative thermal expansion compound Zn(CN)2 is investigated by quasielastic neutron scattering technique in the temperature range 170-320 K. Significant quasielastic broadening is observed above the phase transition temperature of about 250 K, however no broadening is observed at 220 K and below. Data at high temperatures are analyzed assuming the CN reorientation. Characteristic time associated with the CN orientation is estimated as 16 ps and 11 ps at 270 and 320 K respectively.
The effects of confining molecular hydrogen within carbon nanohorns are studied via high-resolution quasielastic and inelastic neutron spectroscopies. Both sets of data are remarkably different from those obtained in bulk samples in the liquid and crystalline states. At temperatures where bulk hydrogen is liquid, the spectra of the confined sample show an elastic component indicating a significant proportion of immobile molecules as well as distinctly narrower quasielastic line widths and a strong distortion of the line shape of the para - ortho rotational transition. The results show that hyd…
A set of sp2 amorphous carbons involving natural mineral shungite carbon and antraxolite as well as two synthetic carbon blacks were investigated by using neutron powder diffraction and inelastic neutron scattering at low temperature. NDP revealed nanographite-like structure of all the samples, stacks of which are formed by basic structure units representing framed graphene molecules of ~2.5 nm in lateral dimension. INS study showed the presence of hydrogen atoms in the BSU framing area as well as of adsorbed water in the samples pores. Simulated INS spectra of adsorbed water showed its mono-l…
We report measurements of the neutron diffuse scattering in a single crystal of the relaxor ferroelectric material 95.5%Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT). We show that the diffuse scattering at high temperatures has a quasielastic component with energy width $\agt$ 0.1 meV. On cooling the total diffuse scattering intensity increases, but the intensity and the energy width of the quasielastic component gradually diminish. At 50 K the diffuse scattering is completely static (i.e.the energy width lies within the limits of our instrumental resolution). This suggests that the dynamics of the…
We show that ZIF-4, a metal-organic framework (MOF) with a zeolitic structure, undergoes a crystal--amorphous transition on heating to 300 $^\circ$C. The amorphous form, which we term a-ZIF, is recoverable to ambient conditions or may be converted to a dense crystalline phase of the same composition by heating to 400 $^\circ$C. Neutron and X-ray total scattering data collected during the amorphization process are used as a basis for reverse Monte Carlo refinement of an atomistic model of the structure of a-ZIF. We show that the structure is best understood in terms of a continuous random netwo…
We have performed quasielastic and inelastic neutron scattering (QENS and INS) measurements from 300 K to 1173 K to investigate the Na-diffusion and underlying host dynamics in Na2Ti3O7. The QENS data show that the Na atoms undergo localized jumps up to 1173 K. The ab-initio molecular dynamics (AIMD) simulations supplement the measurements and show 1-d long-ranged diffusion along the a-axis above 1500 K. The simulations indicate that the occupancy of the interstitial site is critical for long-range diffusion. The nudged-elastic-band (NEB) calculation confirmed that the activation energy barrie…
High-resolution neutron backscattering techniques are exploited to study the elastic and quasi-elastic response of the high-density amorphous (HDA), the low-density amorphous (LDA) and the crystalline ice Ic upon temperature changes. Within the temperature ranges of their structural stability (HDA at T > 80 K, LDA at T > 135 K, ice Ic at T < 200 K) the Debye-Waller factors and mean-square displacements characterise all states as harmonic solids. During the transformations HDA->LDA (T ~ 100 K), LDA->Ic (T ~ 150K) and the supposed glass transition with Tg ~ 135 K no relaxation processes can be d…
Solid-state cooling using barocaloric materials is a promising avenue for eco-friendly, inexpensive and highly efficient cooling. To design barocaloric compounds ready for deployment, it is essential to understand their thermodynamic behaviour under working conditions. To this end, we have studied the rotational dynamics in the molecular-ionic crystal ammonium sulfate under pressure, providing detailed insight into the origin of its large barocaloric effect. Using quasielastic neutron scattering experiments, we show that rotation of the ammonium cations is facilitated by pressure in the low-en…
We study the structural properties and the collective microscopic dynamics of atoms in the amorphous metallic alloy $Ni_{33}Zr_{67}$ at the temperature $T=300K$ by molecular dynamics simulations. The calculated equilibrium structural and dynamical characteristics are compared with the experimental data on neutron diffraction and on inelastic X-ray scattering. We present the interpretation of observed structural relaxation of the microscopic density fluctuations of particles for amorphous metallic alloy in the framework of the recurrent relation approach. The results of theoretical calculations…
We demonstrate that the amorphous material PAF-1, C[(C6H4)2]2, forms a continuous random network in which tetrahedral carbon sites are connected by 4,4'-biphenyl linkers. Experimental neutron total scattering measurements on deuterated, hydrogenous, and null-scattering samples agree with molecular dynamics simulations based on this model. From the MD model, we are able for the first time to interrogate the atomistic structure. The small-angle scattering is consistent with Porod scattering from particle surfaces, of the form Q^{-4}, where Q is the scattering vector. We measure a distinct peak i…
We measured two magnetic modes with finite and discrete energies in an antiferromagnetic ordered phase of a geometrically frustrated magnet MgCr2O4 by single-crystal inelastic neutron scattering, and clarified the spatial spin correlations of the two levels: one is an antiferromagnetic hexamer and the other is an antiferromagnetic heptamer. Since these correlation types are emblematic of quasielastic scattering with geometric frustration, our results indicate instantaneous suppression of lattice distortion in an ordered phase by spin-lattice coupling, probably also supported by orbital and cha…
Previous studies of the structure of liquid water under pressure performed by neutron diffraction, allowed us to establish two structural limits in liquid water. These two limits are closely connected to the two known forms of amorphous ice : the low density amorphous ice (LDA) and the high density amorphous ice (HDA). In the present paper, we propose some interpretation of our data in terms of a two level type model of water. This leads to show some evidence of a liquid-liquid phase transition in liquid supercooled water. The result looks in agreement with recent computer simulations that inc…
Ferroelectric phase transition in the semiconductor Sn2P2S6 single crystal has been studied by means of neutron scattering in the pressure-temperature range adjacent to the anticipated tricritical Lifshitz point (p=0.18GPa, T=296K). The observations reveal a direct ferroelectric-paraelectric phase transition in the whole investigated pressure range (0.18 - 0.6GPa). These results are in a clear disagreement with phase diagrams assumed in numerous earlier works, according to which a hypothetical intermediate incommensurate phase extends over several or even tens of degrees in the 0.5GPa pressure…
The nanostructure of hydrogenated amorphous silicon (a Si:H) is studied by a combination of small-angle X-ray (SAXS) and neutron scattering (SANS) with a spatial resolution of 0.8 nm. The a-Si:H materials were deposited using a range of widely varied conditions and are representative for this class of materials. We identify two different phases which are embedded in the a-Si:H matrix and quantified both according to their scattering cross-sections. First, 1.2 nm sized voids (multivacancies with more than 10 missing atoms) which form a superlattice with 1.6 nm void-to-void distance are detected…
We report elastic and inelastic neutron scattering experiments on different amorphous ice modifications. It is shown that an amorphous structure (HDA') indiscernible from the high-density phase (HDA), obtained by compression of crystalline ice, can be formed from the very high-density phase (vHDA) as an intermediate stage of the transition of vHDA into its low-density modification (LDA'). Both, HDA and HDA' exhibit comparable small angle scattering signals characterizing them as structures heterogeneous on a length scale of a few nano-meters. The homogeneous structures are the initial and fina…
We report a synthesis route to grow iron nitride thin films with giant saturation magnetization (Ms) through an N inter-diffusion process. By post annealing Fe/Fe-N structured films grown on GaAs(001) substrates, nitrogen diffuses from the over-doped amorphous-like Fe-N layer into strained crystalline Fe layer and facilitates the development of metastable Fe16N2 phase. As explored by polarized neutron reflectometry, the depth-dependent Ms profile can be well described by a model with the presence of a giant Ms up to 2360 emu/cm3 at near-substrate interface, corresponding to the strained region…
Cu2Se and Cu2S are excellent model systems of superionic conductors with large diffusion coefficients that have been reported to exhibit different solid-liquid-like Cu-ion diffusion. In this paper, we clarify the atomic dynamics of these compounds with temperature-dependent ab-initio molecular dynamics (AIMD) simulations and inelastic neutron scattering (INS) experiments. Using the dynamical structure factor and Van-Hove correlation function, we interrogate the jump-time, hopping length distribution and associated diffusion coefficients. In cubic-Cu2Se at 500 K, we find solid-like diffusion wi…
We report on investigations of phonons and lithium diffusion in LiAlO$_2$ based on inelastic neutron scattering (INS) measurements of the phonon density of states (DOS) in γ-LiAlO$_2$ from 473 K to 1073 K, complemented with ab-initio molecular dynamics (AIMD) simulations. We find that phonon modes related to Li vibrations broaden on warming as reflected in the measured phonon DOS and reproduced in simulations. Further, the AIMD simulations probe the nature of lithium diffusion in the perfect crystalline phase (γ-LiAlO$_2$), as well as in a structure with lithium vacancies and a related amorpho…
Spin and lattice dynamics of CaMn7O12 ceramics were investigated using infrared, THz and inelastic neutron scattering (INS) spectroscopies in the temperature range 2 to 590 K, and, at low temperatures, in applied magnetic fields of up to 12 T. On cooling, we observed phonon splitting accompanying the structural phase transition at Tc = 450K as well as the onset of the incommensurately modulated structure at 250 K. In the two antiferromagnetic phases below T_N1 = 90K and T_N2 = 48 K, several infrared-active excitations emerge in the meV range; their frequencies correspond to the maxima in the m…
The deceptively simple inorganic salt ammonium sulfate undergoes a ferroelectric phase transition associated with a very large entropy change and both electrocaloric and barocaloric functionality. While the structural origins of the electrical polarisation are now well established, those of the entropy change have been controversial for over fifty years. This question is resolved here using a combination of DFT phonon calculations with inelastic neutron scattering under variable temperature and pressure, supported by complementary total and quasielastic neutron scattering experiments. A simple…
We have investigated low energy nuclear spin excitations in double perovskite compounds R$_2$CoMnO$_6$ (R = Y,Tb) by inelastic neutron scattering with a high-resolution back-scattering spectrometer. We observed inelastic signals at about 2.1 $μ$eV for Y$_2$CoMnO$_6$ and also for Tb$_2$CoMnO$_6$ at T = 2 K in both energy loss and energy gain sides. We interpret these inelastic peaks to be due to the transitions between the hyperfine split nuclear levels of $^{59}$Co nucleus. The inelastic peaks move towards the central elastic peak and finally merge with it at the magnetic ordering temperature …
The magnetic order and the spin dynamics in the antiferromagnetic entropy-stabilized oxide (Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)O (MgO-ESO) have been studied using muon spin relaxation ($μ$SR) and inelastic neutron scattering. We find that antiferromagnetic order develops gradually in the sample volume as it is cooled below 140 K, becoming fully ordered around 100 K. The spin dynamics show a critical slowing down in the vicinity of the transition, and the magnetic order parameter grows continuously in the ordered state. These results indicate that the antiferromagnetic transitio…
Comprehensive Research Organization for Science and Society (CROSS)（综合科学研究组织）；Tohoku University（东北大学）；Japan Atomic Energy Agency (JAEA)（日本原子能研究开发机构）；Ibaraki University（茨城大学）；Tokyo City University（东京都立大学）；The University of Tokyo（东京大学）
The purpose of this work is to study the change in the structure of the Ge-Se network upon doping with Ag. The total structure factor S(Q) for two samples has been measured by neutron diffraction using the two-axis diffractometer dedicated to structural studies of amorphous materials, D4, at the Institut Laue Langevin. We have derived the corresponding radial distribution functions for each sample and each temperature, which gives us an insight about the composition and temperature dependence of the correlation distances and coordination numbers in the short-range. Our results are compatible w…
I discuss elastic properties of neutron star crust in the framework of static Coulomb solid model when atomic nuclei are treated as non-vibrating point charges; electron screening is neglected. The results are also applicable for solidified white dwarf cores and other materials, which can be modeled as Coulomb solids (dusty plasma, trapped ions, etc.). I demonstrate that the Coulomb part of the stress-strain tensor has additional symmetry: contraction $B_{ijil}=0$. It does not depend on the structure (crystalline or amorphous) and composition. I show as a result of this symmetry the effective …
We present a neutron spectroscopy based method to study quantitatively the partial miscibility and phase behaviour of an organic photovoltaic active layer made of conjugated polymer:small molecule blends, presently illustrated with the regio-random poly(3-hexylthiophene-2,5-diyl) and fullerene [6,6]-Phenyl C$_{61}$ butyric acid methyl ester (RRa-P3HT:PCBM) system. We perform both inelastic neutron scattering and quasi-elastic neutron scattering measurements to study the structural dynamics of blends of different compositions enabling us to resolve the phase behaviour. The difference of neutron…
Iron self-diffusion in nano-composite FeZr alloy has been investigated using neutron reflectometry technique as a function of applied compressive stress. A composite target of (Fe+Zr) and (57Fe+Zr) was alternatively sputtered to deposit chemically homogeneous multilayer (CHM) structure, [Fe75Zr25/57Fe75Zr25]10. The multilayers were deposited on to a bent Si wafer using a 3-point bending device. Post-deposition, the bending of the substrate was released which results in an applied compressive stress on to the multilayer. In the as-deposited state, the alloy multilayer forms an amorphous phase, …
Below the melting temperature $T_m$ crystals are the stable phase of typical elemental or molecular systems. However, cooling down a liquid below $T_m$, crystallization is anything but inevitable. The liquid can be supercooled, eventually forming a glass below the glass transition temperature $T_g$. Despite their long lifetimes and the presence of strong barriers that produces an apparent stability, supercooled liquids and glasses remain intrinsically metastable state and thermodynamically unstable towards the crystal. Here we investigated the isothermal crystallization kinetics of the prototy…
