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Lithium–indium diselenide (LiInSe2) is a new semiconductor material, sensitive to the thermal neutrons. LiInSe2 compound was synthesized from Li (99.99%), In (99.999%) and Se (99.999%). The growth of LiInSe2 single crystals was performed using the vertical option of Bridgman–Stockbarger method. The crystals were characterized using the electrical conductivity and optical spectroscopy methods. Stoichiometric composition of the LiInSe2 was confirmed by the high precision chemical analysis, as well as by X-ray diffraction. Compact 252Cf neutron source with the activity 6.3 × 105 n/s allowed measuring amplitude characteristics and defining the optimal operating voltage for neutron detection. Time-of-flight neutron spectra were measured at the fast pulsed research reactor IBR-2 at the Joint Institute for Nuclear Research.

The phase composition and spatial distribution of chemical components in the volume of coins of medieval Volga Bulgaria are studied using the neutron-diffraction- and neutron-tomography methods. Two coins belonging to different time periods of this medieval state are studied: a Samanid multidirham dating from the first half of the 10th Century and a silver dirham dating from the period of the reign of the Bulgarian emir Bulat-Timur. It is established that both coins consist of a copper-silver alloy. In the Samanid multidirham, the average volume contents of copper and silver are found to be about 50%. Minor spatial variations in the chemical composition are found in the volume of the multidirham under study. It is established that the volume average silver content in the Bulat-Timur dirham is about 95%.

Defect structures of BaTiO3 nanoparticles annealed in the air and their correlation with magnetic properties have been studied. As main research techniques, complementary methods such as XPS and positron annihilation lifetime spectroscopy were used. It was found that low-temperature annealing creates additional oxygen vacancies in nanoparticles both inside and on the nanoparticle surface, and high-temperature annealing favors the reduction of Ti. These changes influence nanoparticle magnetism and occur due to the charge compensation process and grain growth mechanism. Performed studies show that complementary XPS and positron annihilation spectroscopy are the effective tools to determine nanoparticle surface defect structure, which can be used to fabricate new rare room-temperature multiferroics materials.

Possible options for modernization of the neutron beam forming system of the DN-6 diffractometer for the study of crystal and magnetic structures of microsamples at high pressures are being considered. It was demonstrated that for samples with the cross-section not exceeding 5 × 5 mm2 the most efficient option would be the use of an elliptical neutron guide. It allows to deliver neutrons for large distances from the source to samples with minimal losses using, as a rule, just one neutron reflection per dimension i.e. one at a side and one at top or bottom. For the present moment due to technical difficulties of such option realization, the simplified solution was proposed. At the end of the curved neutron guide it is planned to install a vertical plane focusing 7-meter-long parabolic section. Such a modernization will increase the neutron flux at the sample by a factor 1.5–3.5 and reduce respectively the typical measurement times.

The applicability of the modified kinematic approximation for simulation of the specular reflection and the diffraction of a neutron beam from regularly ordered nanostructured objects on the surface and in the surface material layer is analyzed. The obtained results are compared with those of the real experiment and simulation of the distorted-wave Born approximation (DWBA). The influence of various factors on the obtained results is analyzed. These factors include the effect of neutron-wave refraction at the interfaces between media, the spectrometer-resolution function, and renormalization of the results for a nonspecular scattering signal based on data obtained for a specular channel. It is shown that, in many cases, it is possible to obtain rather good agreement with the experimental data and with the results of calculations using DWBA methods and of calculations using the Parratt algorithm.

Neutron diffraction at grazing incidence was simulated for the regularly ordered nanostructures on the surface and in the near-surface volume of a homogeneous matrix. Silicon was used as a matrix material and nanoparticles consisting of gold or nickel. This allowed obtaining a good scattering contrast between the matrix and nanoparticles and, as a result, high contrast diffraction patterns. It is shown that the modified kinematic approximation which takes into account the refraction of a neutron wave at the interface makes it possible to obtain a reasonable agreement with the available experimental data. In addition, it was demonstrated that in contrast to the traditional diffraction on point-like scattering centers, some unusual systematic absences could be observed due to the experiment geometric conditions and the finite geometric sizes of the nanoparticles. The results demonstrate that modified kinematic approximation can be successfully used to model non-specular neutron scattering from near-surface nanostructures and thereby facilitate the interpretation of experimental results.

The supramolecular organization of the visual pigment rhodopsin in the photoreceptor membrane remains contentious. Specifically, whether this G protein-coupled receptor functions as a monomer or dimer remains unknown, as does the presence or absence of ordered packing of rhodopsin molecules in the photoreceptor membrane. Completely opposite opinions have been expressed on both issues. Herein, using small-angle neutron and X-ray scattering approaches, we performed a comparative analysis of the structural characteristics of the photoreceptor membrane samples in buffer, both in the outer segment of photoreceptor cells, and in the free photoreceptor disks. The average distance between the centers of two neighboring rhodopsin molecules was found to be ~5.8 nm in both cases. The results indicate an unusually high packing density of rhodopsin molecules in the photoreceptor membrane, but molecules appear to be randomly distributed in the membrane without any regular ordering.

The applicability of the modified kinematic approximation to describe the off-specular neutron scattering from interfaces between media is analyzed. It is demonstrated that in some cases one can expect not only a qualitative but also a quantitative agreement between the data and the results of experiments and calculations based on more accurate techniques. Diffuse scattering from rough surfaces and thin films with correlated and noncorrelated roughness of the upper and lower interfaces and the neutron diffraction by stripe magnetic domains and magnetic domains with a random size distribution (magnetic roughness) are considered as examples.

Lithium-indium di-selenide (LiInSe2) is a semiconductor material, which has been shown promising for applications in nonlinear optics and neutron detection. LiInSe2 crystals of optical quality, of different (from greenish to red) color were grown. Analysis of the fundamental absorption edge shows allowed direct band-to-band transitions and reveals structural disorder leading to the blurring of the edges of valence and conduction bands. Photoluminescence (PL) intensity is low in LiInSe2 of stoichiometric composition and increases after sample annealing in Se vapors. A narrow line at 408 nm is associated with free excitons. Analysis of PL and PL excitation spectra allows one to associate broad emission bands with point defects as well as with self-trapped excitons. The mean positron lifetime increases after annealing in Se vapor as a result of changes of the dominating defect type. For red crystals only big voids with lifetime of about 1021 ps are observed. Both methods suggest that greenish and red coloring of LiInSe2 are due to Se vacancies and interstitial Se atoms, respectively.

The crystal structure of the tetragonal layered cobalt oxide LaSrCoO4 has been studied by means of neutron diffraction at high pressures up to 5.8 GPa in temperature range 7–300 K. The pressure and temperature behaviour of the lattice parameters, including lattice parameters, unit cell volume, and interatomic bond lengths, have been obtained. The anisotropic compression of lattice parameters as well as Co-O bond lengths of the oxygen octahedra have been revealed. The anomalous thermal volume expansion at high pressure are observed, indicative for the pressure induced spin state crossover of Co3+ ions from the mixed low spin – high spin (LS + HS) state at room temperature towards the low spin (LS) ground state. The structural mechanisms of the spin state crossover are discussed.

A new gaseous annular sectional thermal-neutron detector for the new neutron diffractometer at the IBR-2 reactor has been designed and manufactured at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research (JINR). The detector is designed to study small-volume samples at high pressure and consists of 16 sections, each one of which is divided into six independent detector elements. We present the main design features of the detector, detecting electronics, data-acquisition and visualization software, and software system for experiment management. The results of the first neutronographic experiments that were carried out with the use of the detector are also presented.

As neutron simulations packages are used for analysis of the expected performance for practically all newly built neutron instruments, possibilities for simulations with polarized neutrons have been relatively underdeveloped. During the last years we developed a new approach for the representation of time-dependent magnetic fields (both in magnitude and direction) for the VITESS simulation package. This allowed us to simulate the neutron spin dynamics in practically all polarized neutron devices (RF neutron flipper, adiabatic gradient RF flipper, the Drabkin resonator, etc.). In this article the above-mentioned VITESS instrument components (modules) will be presented and the simulated performance of a number of polarized neutron scattering instruments (NRSE, MIEZE, SESANS, etc.) will be demonstrated. Thus, we practically complete the polarized neutron suite of the VITESS, which seems sufficient for the simulation of performance of any existing polarized neutron scattering instrument. Future work will be concentrated on developments of dedicated sample modules (kernels) to allow for virtual experiments with VITESS.

We consider a new configuration for a neutron small angle scattering instrument at the pulsed IBR-2M reactor with a mixed (cold and thermal) moderator system. This system provides added-up spectra from the cold and thermal parts of the moderator. We have installed the spectrometer using a special collimation system formed by two parts: primary with neutron optics element (divergent neutron guide) and secondary (installed after the divergent neutron guide) with a multiple pinhole collimation system. Our efforts have the goal to obtain smaller Q min values (as well as higher resolution) with the possibilities to take advantage of an increased neutron flux compared with the present SANS spectrometer in the limited beam hall size. The Monte Carlo simulations will be used to choose and optimize the spectrometer and extraction system using VITESS software package.

Supramolecular organization of rhodopsin in the photoreceptor membrane was investigated by small-angle neutron scattering method. The experiments, which were performed with mixtures of heavy/light water as solvent (contrast variation method), were aimed at obtaining information about the lipid and protein components of the photoreceptor disc membrane separately. It was shown that the packaging density of the rhodopsin molecules in the photoreceptor membrane was unusually high: the distance between the centers of the molecules was approximately 56 A. The probability of the monomeric state of rhodopsin molecules in the photoreceptor membrane, according to the data obtained, is rather high.

Nowadays practically all leading centers engaged in neutron research of condensed matter, are equipped with highly efficient, high count rate neutron detectors based on multiwire proportional chambers of large area (up to 65×65 cm 2 ) with coordinate resolution of 1–10 mm, microstrip, scintillation and thermoluminescence detectors, and this allows them to make the most efficient use of their neutron sources. In many centers neutron position-sensitive detectors (PSD) of new type with submillimeter coordinate resolution, large area and high count rate are being developed. In order to keep leading positions in the field of condensed matter investigations using one of the best neutron sources in the world—the IBR-2 reactor—it is vitally important to bring up-to-date the techniques of registration of neutrons. In particular, it is necessary to develop the advanced neutron position-sensitive detectors. The report gives an overview of present activities at the Frank Laboratory of Neutron Physics of JINR in this field.

The experience gained in the last 15 years of experimental studies of large-scale structures with the SANS instrument at the IBR-2 pulsed reactor in Dubna shows that some parameters of the spectrometer can be improved. In particular, it concerns reduction of the fast neutron and gamma backgrounds that limit the possibilities of studying weakly scattering objects. Another direction of improvement is to reduce a minimum momentum transfer value Q min to study objects with larger characteristic dimensions. The paper investigates several configurations of the SANS machine at IBR-2. The Monte Carlo codes are used to calculate the parameters of such virtual instruments. An optimal instrument structure is proposed.

Structure and orientational disorder of ammonium ions in the high-temperature phase I of ND4I were studied by reverse Monte Carlo and maximum entropy methods using powder neutron diffraction data. The ammonium ions were found to perform a librational motion with an average angular libration amplitude of γ=20° and reorientational motion by 39° jumps of the N–D bonds between (xxx) and (xxz) positions in the structure. Reorientations by 90° jumps were found to have a low probability.

The location of protons in crystals and their dynamics are successfully studied by the methods of neutron scattering. In contrast to X-rays, the cross-section of the neutron–nucleus interaction does not have regular dependence on the atomic weight. Light atoms, like hydrogen, can scatter neutrons more effectively than heavy ones and therefore are more easily located in the structure with the help of neutron diffraction. The absence of selection rules in inelastic neutron scattering allows to observe all vibrational modes of the crystal. The anomalously large incoherent neutron scattering cross section of hydrogen in comparison to other elements considerably simplifies the interpretation of inelastic and quasielastic scattering results. In the present review examples of the complex use of different neutron scattering methods for the study of structure and dynamics of some superprotonic (with proton conductivity higher than 10 −4 Ohm −1 cm −1 ) conductors with hydrogen bonds is given.

The sequence of phase transitions at temperatures from 290 to 420 K in the crystals of Cs5H3(SO4)4·0.5H2O (CTSM) and Cs5D3(SO4)4·0.5D2O (DCTSM) was studied by Brillouin light scattering and neutron diffraction. Anomalies in the temperature dependences of the velocity and damping of hypersonic acoustic phonons in the vicinity of 360 K were observed in the CTSM crystal. In contrast, no anomalies were found in the DCTSM crystal. Preliminary analysis of neutron diffraction data does not show symmetry changes in the temperature range studied. Thus it has been found that deuteration of the CTSM crystals leads to a change in the sequence of phase transitions.

The total structure factor for deuterated ammonium chloride measured by neutron diffraction has been modeled using the reverse Monte Carlo method. The results show that the orientational disorder of the ammonium ions consists of a local librational motion with an average angular amplitude α=17° and reorientations of ammonium ions by 90° jumps around two-fold axes. Reorientations around three-fold axes have a very low probability.

Caesium hydrogen sulphate is one of the most extensively studied superprotonic conductors with hydrogen bonds. A first order phase transition, from the low conductivity to the high conductivity phase, takes place at 414 K. The crystallographic structure of both phases has been established using high-resolution neutron powder diffraction. Quasielastic neutron scattering has provided information about the spatial and temporal characteristics of proton transport. In the present paper we report the results of reverse Monte Carlo modelling of neutron diffraction (total scattering) data which makes it possible to obtain the diffusion pathways for protons. The results are in good agreement with the qualitative model for proton transport proposed previously; in particular we show clearly that the proton motion is highly correlated with the rotation of the sulphate groups. In the low temperature phase we identify a weak correlation between protons and oxygens on the next-nearest-neighbour sulphate group which increases with temperature and probably drives the phase transition.

The total structure factor of BaTiO3 obtained by neutron powder diffraction in the temperature range 360–430 K in the vicinity of ferroelectric phase transition has been modeled by the reverse Monte Carlo method. A presence of disordered displacements of Ti atoms due to dynamical tetragonal elongations of unit cells and off-centered sites of Ti atoms in paraelectric phase in the vicinity of the ferroelectric phase transition was observed. Both features result in the anomalous increase of mean square displacements of Ti atoms and reflect the coexistence of displacive and order–disorder components in the ferroelectric phase transition.

K1−x(NH4)xH2PO4 mixed crystals which in a certain composition range exhibit proton glass properties were studied using neutron diffraction and quasielastic neutron scattering. Anomalous temperature behaviour of the structure and rotational diffusion of ammonium groups are discussed.

A study of the rotational dynamics of NH4 ions in the paraelectric phase of mixed crystals of K1-x(NH4)xH2PO4 by quasielectric neutron scattering is reported. For high NH4 concentrations (x=0.9) no anomalous behaviour was found and the model of NH4 ion jumps between equivalent orientations in the crystal gave a good description of the experimental data. In contrast the crystal with x=0.6, which forms a protonic dipolar glass state at low temperatures, revealed an unusual temperature dependence of the elastic incoherent structure factor far above the glass formation boundary. This temperature dependence is analysed in the framework of the model of dynamical cluster formation in the paraelectric phase. The order parameter for the gradually condensing NH4 groups is obtained. The results are compared with data obtained by other methods on related compounds.

Lattice dynamics of the ordered gamma -ZrH phase was studied by inelastic neutron scattering (INS). It was found that the hydrogen optical peak in the INS spectrum had three maxima at energy transfers of 141.5, 148.7 and 156.3 meV. The peak was accurately described using the Born-von Karman model. Anharmonicity of hydrogen vibrations was evident in the high-energy range of the spectrum from a strong sharp peak at E=269.7 meV and broader features below the bands of free-multiphonon scattering. These anharmonic phenomena were attributed to the bound multiphonon states (biphonon, triphonon, tetraphonon and their combinations), and the values of the binding energies of biphonons and triphonons were obtained from the experimental data.

The crystal structure and the lattice dynamics of the ordered gamma -ZrD phase were studied by means of neutron diffraction and inelastic neutron scattering (INS). It was found that the actual structure of the gamma phase is orthorhombic, space group Cccm, rather than tetragonal as previously believed. The one-phonon deuterium optical band in the INS spectrum was observed at an energy transfer of 107 meV (with the main feature at 103.4 meV), which is higher than the deuterium vibrational energies for all other phases of the Zr-D system. Distinct features were also observed in the INS spectrum below the free multiphonon bands, which were explained as the bound multiphonon states.

The inelastic neutron scattering spectra of caesium hydrogen sulphate (CsHSO4) in three different low-temperature crystallographic phases have been obtained. One of the phases was obtained by applying a pressure of 1.7 GPa at ambient temperature. A comparative analysis of the vibrational spectra is presented. It is shown that the proton dynamics in the hydrogen bonds of the two ambient pressure phases are almost totally decoupled from the dynamics of the other atoms. Anharmonicity plays an important role in the dynamical properties of the ambient pressure phases. It is observed that the effects of anharmonicity in one of the ambient pressure phases can be explained within the framework of the simple anharmonic oscillator model. For the other ambient pressure phase the model of bound two-phonon (biphonon) states is required to explain the data. On the other hand in the high-pressure crystalline phase the proton dynamics exhibit an almost purely harmonic behaviour coupled with a strong interaction between the hydrogen-bond bending modes and SO42- ion internal vibrations.

Oriented stacks of purple membrane (PM) were studied with high-resolution quasielastic incoherent neutron scattering (QINS). The experiments were carried out under dark conditions at room temperature, for two different orientations, such that the momentum transfer Q was either parallel or perpendicular to the membrane plane at 90° scattering angle. The samples were equilibrated in H 2 O as well as in D 2 O, both at 100% relative humidity. The analysis of the spectra shows that the hydration water is performing anisotropic translational diffusion (TD), preferentially parallel to the membrane plane, with a diffusion coefficient about 5 times smaller than that of bulk water at room temperature. From the behaviour at large scattering angles an average jump distance of about 4 A was estimated. This fast translational diffusion process is accompanied by an even faster local diffusive motion of the water protons. The approximate description of the latter by a rotational diffusion model for H 2 O molecules yields a quasielastic line width of about 70 μeV (HWHM). The observed local diffusive motion of protons in PM is an order of magnitude slower (angular average of the corresponding linewidth: HWHM = 9 μeV).

The structures of different phases of caesium hydrogen sulphate are discussed. The interrelation of structural features and high protonic mobility in the superprotonic phase is established. The symmetry and unit cell parameters of the phases realized at high pressures are given. The results of a study of the lattice dynamics of several crystallographic phases are presented.

On the basis of a simple model for the interatomic potential the lattice dynamics of Ba 1−x K x BiO 3 were calculated. Some features of the structural phase diagram, the optical and neutron spectroscopy data can be explained in spite of the simplicity of the model. To compare the model calculations with the experiment a time-of-flight neutron scattering study of the lattice dynamics of Ba 1−x K x BiO 3 for x =0.0 and x =0.4 has been performed for the temperatures 10 K, 80 K and 290 K. The experimental results are in good agreement with previous measurements. No temperature effects were found for the generalized phonon density of states. The phonon spectrum of a superconducting sample reveals fewer Van Hove singularities and softens in comparison with that of the nonsuperconducting one. The calculated phonon density of states was found to be in qualitative agreement with experiment.

The diffusion of protons in the superionic phase of CsHSO4 was investigated by quasielastic neutron scattering (QNS) on the IRIS spectrometer at the pulsed spallation neutron source ISIS, Rutherford Appleton Laboratory, UK. Two processes with different characteristic times could be distinguished: long-range translational diffusion with a diffusion coefficient D=(1.00-1.17)*10-7 cm2 s-1 (for a temperature range from 423 to 448 K) and jump rotation of HSO4 groups between two possible orientations, the corresponding nonequivalent proton sites being 2.3 AA apart.

Neutron guides are widely used to transport the neutrons from the moderator to the sample. Due to the constructive features of the ring corridor of the fast pulsed reactor IBR-2, the minimal distance between the moderator and the guide entrance is around 6 m. The main goal of the paper is to optimize the neutron optical system between the moderator and the entrance of the new neutron guides. Using Monte Carlo simulations we calculate the possible best gain of the neutron flux density at the guide exit. After the described optimization process, the optimal system is obtained. The recommendations for construction of the new beam line are provided too. Similar technique and the proposed system could be easily adapted for another similar beam line at the neutron sources.

The crystal structure and the mechanism of proton transport for the MeXAO 4 (Me=Cs, Rb; X=H, D; A=S, Se) family of protonic conductors is analyzed on the basis of the results obtained for CsHSO 4 and its deuterated derivative. Some peculiarities of the superionic phase transition are explained. The characteristics of the proton diffusion are determined quantitatively.

Determination structurale a 300 K (phase basse conductivite) et 448 K (phase super-ionique). Utilisation de la methode Rietveld afin de determiner les positions atomiques, les occupations de sites et les facteurs de temperature des atomes legers D et O. Le mecanisme de diffusion de D est discute. A 300 K, cristallisation dans P2 1 /c avec a=7,78013, b=8,13916, c=7,72187 A, β=110,8720°, affinement jusqu'a R=4,19%. A 448 K, cristallisation dans Z4 1 /amd avec a=5,74147, c=14,31508 A, affinement jusqu'a R=2,21%

In our report, we present first results of the investigation of the behaviour of acoustic phonons at the phase transformation from the dynamically to statistically disordered network of hydrogen bonds in the Cs5D3(SO4)4·D2O (PCTS) crystal. Neutron scattering experiments at room temperature were performed on a triple axis spectrometer. Dispersion of the Ta phonon along the [0 0 ξ] direction in a hexagonal phase was observed. The temperature dependencies of the TA and mixed phonon branches along [1 1 0] were studied.

Cesium hydrogen sulphate is one of the most extensively studied superprotonic conductors with hydrogen bonds. The first-order phase transition, from the low-conductivity to high conductivity phase ...

The lattice dynamics of KH 2 PO 4 was studied at 30 K at ambient pressure (ferroelectric phase) and a pressure of 20 kbar (paraelectric phase). Dramatic changes in the spectra are discussed in the context of the mechanism of ferroelectric phase transition.

A new gas multi-section ring-shaped detector (MSRD) for thermal neutrons has been developed at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) for ...

Caesium hydrogen sulphate (CsHSO4) shows a rich variety of phases in the pressure-temperature phase diagram. The crystal structures of these phases have been studied by the neutron-diffraction method. The lattice dynamics of several crystallographic phases have also been studied by the inelastic neutron scattering. It is shown that anharmonicity plays an important role in the dynamic properties of phases occurring at ambient pressure. High pressure reduces the effects of anharmonicity and the crystal phase which appears at a pressure of 1.7 GPa exhibits harmonic behaviour.

K 1− x (NH 4 ) x H 2 PO 4 (KADP) mixed crystals exhibit proton-glass behaviour over a certain composition range. The results of neutron-diffraction, high-resolution inelastic and quasielastic neutron scattering studies of KADP are presented. The anomalous behaviour of the proton glass system (0.2 ⩽ × ⩽ 0.8) is discussed.

The spectra of five samples recorded at 20 K with the NERA spectrometer from ∼ 0 to 1600 cm −1 (at JINR, Dubna, Russian Federation) are reported: chemical γ -MnO 2 (CMD SEDEMA WSA), electrochemical γ -MnO 2 (EMD TEKKOSHA), lamellar Bi + δ -MnO 2 , δ -MnO 2 2H 2 O and NH 4 + α -MnO 2 . The relative concentrations of the protonic species are estimated.

The lattice dynamics of the ordered γ -TiH(D) and γ-ZrH(D) phases with essentially one-dimensional H H (D—D) interaction have been studied by inelastic neutron scattering. The bound multiphonon states (biphonon, triphonon, tetraphonon and their combinations) were observed in the spectra, and the binding energies were obtained from the experimental data.

The structural and magnetic properties of iron nanoparticles formed in an aluminium matrix by combined helium and iron ions irradiation have been studied by small-angle X-ray scattering and susceptibility measurements. The formation of nanoparticles with average size of about 6.8 nm under iron ions irradiation has been found. The additional posterior irradiation with helium ions leads to the iron nanoparticles ordering with correlation length of 7.2(1) nm. The characteristic radius of iron nanoparticles and fractal dimension of the Al matrix were determined and magnetic properties of the Fe-Al nanomaterials were analysed.

This paper describes studies of the effect of deuteration on the structure and dynamics of the Cs5H3(SO4)4·0.5H2O lattice at low temperatures by inelastic neutron scattering and neutron powder diffraction. It has been found that diffraction spectra of Cs5H3(SO4)4·0.5H2O and its deuterated analog with a high deuterium concentration differ by the number of reflex.