High Resolution Fourier Diffractometer Research Articles

Wide-Aperture Backscattering Detector (BSD-A) for The High-Resolution Fourier Diffractometer

The high-resolution Fourier diffractometer (HRFD) has been in routine operation since 1994 at the long-pulse neutron source, the IBR-2 reactor, in Dubna. Its fast Fourier chopper provides probably the best compromise between very high resolution in reciprocal space (Δd/d ≈ 0.001) and the intensity. For further improving intensity of TOF-diffraction pattern, a wide-aperture ring backscattering detector (BSD) has been developed on the basis of ZnS(Ag)/6LiF scintillator. BSD is designed in the form of 6 concentric rings, each of which is subdivided into 12 identical parts. The main parameters of the detector are the following: range of scattering angles is 2θ = (133 - 175) degrees, covered solid angle is Ωd ≈ 2.0 sr, average percentage absorption efficiency gets closer to 85%, geometrical contribution to resolution function does not exceed Δd/d = 0.0005. In the report the concept of the detector is described and its data acquisition system is presented. The start of operation of the detector at the HRFD is scheduled for 2024.

Wide-aperture back-scattering detector (BSD) for the High-Resolution Fourier Diffractometer (HRFD) at the IBR-2 reactor

The high-resolution Fourier diffractometer (HRFD) operates at the IBR-2 pulsed reactor, on which the correlation method of data registering has been implemented using a fast Fourier chopper and specialized electronics. A wide-aperture ring back-scattering detector for HRFD has been developed. The detector consists of six Z n S ( A g ) / 6 L i F-scintillation rings, each one of which is divided into 12 sections. Main parameters of this detector: covered solid angle 2 θ = ( 133 − 175 ) ∘ ; Ω d ≈ 2.0 sr; average absorption efficiency 85 %, geometric contribution to resolution Δ d / d < 0.0005. The concept of a detector and its data acquisition system are presented.

Neutron-diffraction study of the cubic-tetragonal phase structural transition in the single crystals of the solid solutions of zirconium and yttrium oxides

Objectives. The determination of the phase relations, crystallographic characteristics, microstructure features, and atomic crystal structure of zirconium oxide crystals that are partially and completely stabilized by yttrium oxide additives, and the identification of the crystallographic and crystal-chemical correlations with the physicochemical properties of single crystals.Methods. The neutron structure of the crystals was studied using the neutron time-of-flight and constant wavelength methods using a high-resolution Fourier diffractometer on the IBR-2 pulsed fast reactor and a four-circle neutron diffractometer “Syntex.” Single crystals were grown by directed crystallization from the melts of mixtures (1 − х)ZrO2 ∙хY2O3 , х = 0.03 and х = 0.12 with different growth rates (10 and 40 mm/h).Results. It was observed that when growing single crystals with x = 0.03–0.05, the crystal was stratified into cubic and tetragonal phases, and the ratio between the phases depended on the growth rate. At a growth rate of 40 mm/h, the content of the cubic phase was insignificant. In the crystals of partially stabilized zirconium dioxide (ZrO2) with the additions of 3 mol % Y2O3, the coherent coexistence of cubic and tetragonal phases was established, and the twin law for a tetragonal component (rotation of unit cell axis by 90° around the a (b) axis) that was observed during the phase transition from high-temperature cubic phase to tetragonal phase was determined. For the fully stabilized zirconium oxide of the cubic symmetry (with 12 mol % Y2O3), the 0.3 Å displacements of oxygen atoms from their partial structural positions in the directions [100] and [111] were determined. These displacements correlated with the directions of the ion transport.Conclusions. Previous studies have shown that the ratio between the cubic and tetragonal phases of the single crystals of the ZrO2 –Y2O3 system depends on the growth rate of the single crystals. The content of Y2O3 in the cubic and tetragonal phases of a single crystal was determined using the non-destructive neutronography method on the same volume sample of a solid solution of this system. Moreover, the displacements of oxygen atoms from the main position of the crystal were determined.

High-resolution neutron Fourier diffractometer at the IBR-2 pulsed reactor: A new concept

The High Resolution Fourier Diffractometer (HRFD) is a neutron time-of-flight spectrometer with a fast Fourier chopper and a correlation mode of data acquisition designed to study atomic and magnetic structures of crystalline materials with high resolution in reciprocal space. The HRFD was constructed in the early 1990s by a collaboration of JINR (Dubna), PNPI (Gatchina) and VTT (Espoo) and began operating routinely in 1994 at the IBR-2 pulsed reactor in Dubna. If correlation analysis is used, the HRFD Δd/d resolution is determined by the maximum rotational speed of the Fourier chopper. For Vmax = 6000 rpm, “high-resolution” patterns are measured by backscattering detectors with Δd/d ≈ 0.0015 despite a very short flight path (L ≈ 20 m) between chopper and sample. Switching to a regular TOF-mode (without Fourier chopper) makes HRFD one of the world’s best high-intensity diffractometers, capable of measuring diffraction patterns in the range of ∼1 min and less. In this paper, the experience of using HRFD at IBR-2 is considered and a possible solution for some technical and methodical problems of Fourier diffractometry at a long-pulse neutron source recognized during its operation is discussed. New possibilities appearing after the recent substantial HRFD upgrade and further perspectives on the method are also presented.

Mössbauer Studies and the Microwave Properties of Al3+- and In3+-Substituted Barium Hexaferrites

The correlation of the chemical composition, the structure, and the microwave characteristic of solid solutions of the BaFe12 – xDxO19 (0.1 ≤ x ≤ 1.2) barium hexaferrite substituted with diamagnetic Al3+ and In3+ ions has been studied. The precise data on the crystal structure have been obtained by powder neutron diffraction using a high-resolution Fourier diffractometer (Dubna, JINR). The data on the distribution of the diamagnetic substituting ions in the hexaferrite structure have been obtained by Mossbauer spectroscopy. The microwave properties (the transmittance and the reflectance) have been studied in the frequency range 20–65 GHz and in external magnetic fields to 8 kOe. It is found that the transmission spectra are characterized by a peak that corresponds to the resonant frequency of the electromagnetic energy absorption, which is due to the ferromagnetic resonance phenomenon. The correlation of the chemical composition, the features of the ion distribution in the structure, and the electromagnetic properties has been revealed. It is shown that external magnetic fields shift the absorption peak of electromagnetic radiation to higher frequencies due to an increase in the magnetocrystal anisotropy. The results enable the conclusion that the features of the intrasublattice interactions and the electromagnetic properties should be explained using the phenomenological Goodenough–Kanamori model.

Мессбауэровские исследования и микроволновые свойства гексаферритов бария с замещением ионами Al-=SUP=-3+-=/SUP=- и In-=SUP=-3+-=/SUP=-

AbstractThe correlation of the chemical composition, the structure, and the microwave characteristic of solid solutions of the BaFe_12 – x D_ x O_19 (0.1 ≤ x ≤ 1.2) barium hexaferrite substituted with diamagnetic Al^3+ and In^3+ ions has been studied. The precise data on the crystal structure have been obtained by powder neutron diffraction using a high-resolution Fourier diffractometer (Dubna, JINR). The data on the distribution of the diamagnetic substituting ions in the hexaferrite structure have been obtained by Mössbauer spectroscopy. The microwave properties (the transmittance and the reflectance) have been studied in the frequency range 20–65 GHz and in external magnetic fields to 8 kOe. It is found that the transmission spectra are characterized by a peak that corresponds to the resonant frequency of the electromagnetic energy absorption, which is due to the ferromagnetic resonance phenomenon. The correlation of the chemical composition, the features of the ion distribution in the structure, and the electromagnetic properties has been revealed. It is shown that external magnetic fields shift the absorption peak of electromagnetic radiation to higher frequencies due to an increase in the magnetocrystal anisotropy. The results enable the conclusion that the features of the intrasublattice interactions and the electromagnetic properties should be explained using the phenomenological Goodenough–Kanamori model.

Evolution of microstructure of niobium carbide NbC0.77 powders

The microstructural evolution of annealed nonstoichiometric niobium carbide NbC0.77 powders subjected to high‐energy ball milling has been investigated by time‐of‐flight (TOF) high resolution neutron diffraction. The diffraction patterns have been collected with the high resolution Fourier diffractometer HRFD by using the TOF mode of data acquisition. The nanocrystalline powders produced by high‐energy milling have an inhomogeneous microstructure, in which two fractions with different particle size and composition can be identified. The average sizes of the coherent scattering regions and microstrains in nanocrystallites with allowance for the anisotropy of the deformation distortions have been estimated. It is shown that TOF neutron diffraction patterns can provide the very accurate data for microstructure analysis of nanocrystalline powders. No superstructure has been observed in the annealed NbC0.77 carbide.

Strong corelation between magnetic and electrical subsystems in diamagnetically substituted hexaferrites ceramics

The BaFe11.9Al0.1O19 M-type hexagonal barium ferrite was obtained by a standard ceramic method (powder synthesis in a solid state reaction method). at 4.2, 50, 100, 200, 300, 400, 630 and 730K via neutron powder diffraction (NPD) on a high-resolution Fourier diffractometer. An anomal microstructural transition on atomic level has been observed in BaFe11.9Al0.1O19 due to transition from a centrosymmetric to a non-centrosymmetric Space Group (SG). The NPD data were successfully refined for both space groups (SG): a centrosymmetric SG #194 (non-polar phase) and a non-centrosymmetric SG #186 (polar phase). The Goodness-offit quality factor (χ2) demonstrated good agreement between experimental data and theoretical model for both SG #194 and for #186. Goodness-offit quality factor (χ2) was better at low temperatures (4.2–150K) for SG #186, while at higher temperatures (630–730K) χ2 was better for SG #194. This might be because of the two different phases in BaFe11.9Al0.1O19 and there are mutual phase transitions at the atomic level. Dual ferroic properties (coexistence of magnetization and polarization) were demonstrated at room temperature in BaFe11.9Al0.1O19. Strong correlation between magnetic and electrical subsystems (magnetoelectrical effect – ME) has been shown. Temperatures dependences of the polarization, magnetization and ME effect were studied.

Magnetostructural phase transitions in NiO and MnO: Neutron diffraction data

Structural and magnetic phase transitions in NiO and MnO antiferromagnets have been studied by high-precision neutron diffraction. The experiments have been performed on a high-resolution Fourier diffractometer (pulsed reactor IBR-2), which has the record resolution for the interplanar distance and a high intensity in the region of large interplanar distances; as a result, the characteristics of both transitions have been determined simultaneously. It has been shown that the structural and magnetic transitions in MnO occur synchronously and their temperatures coincide within the experimental errors: Tstr ≈ Tmag ≈ (119 ± 1) K. The measurements for NiO have been performed with powders with different average sizes of crystallites (~1500 nm and ~138 nm). It has been found that the transition temperatures differ by ~50 K: Tstr = (471 ± 3) K, Tmag = (523 ± 2) K. It has been argued that a unified mechanism of the “unsplit” magnetic and structural phase transition at a temperature of Tmag is implemented in MnO and NiO. Deviation from this scenario in the behavior of NiO is explained by the quantitative difference—a weak coupling between the magnetic and secondary structural order parameters.

High-resolution neutron diffraction study of microstructural changes in nanocrystalline ball-milled niobium carbide NbC0.93

High resolution neutron diffraction was applied for elucidating of the microstructural evolution of nanocrystalline niobium carbide NbC0.93 powders subjected to high-energy ball milling. The diffraction patterns were collected with the high resolution Fourier diffractometer HRFD by using the reverse time-of-flight (RTOF) mode of data acquisition. The traditional single diffraction line analysis, the Rietveld method and more advanced Whole Powder Pattern Modeling technique were applied for the data analysis. The comparison of these techniques was performed. It is established that short-time milling produces a non-uniform powder, in which two distinct fractions with differing microstructure can be identified. Part of the material is in fact milled efficiently, with a reduction in grain size, an increase in the quantity of defects, and a corresponding tendency to decarburize reaching a composition NbC0.80 after 15h of milling. The rest of the powder is less efficiently processed and preserves its composition and lower defect content. Larger milling times should have homogenized the system by increasing the efficiently milled fraction, but the material is unable to reach a uniform and homogeneous state. It is definitely shown that RTOF neutron diffraction patterns can provide the very accurate data for microstructure analysis of nanocrystalline powders.

Correlation Fourier diffractometry: 20 Years of experience at the IBR-2 reactor

The high-resolution Fourier diffractometer (HRFD) was commissioned at the IBR-2 pulsed reactor at FLNP JINR in 1994. The specific feature of the HRFD design is the use of fast Fourier chopper for modulating the primary neutron beam intensity and the correlation method of diffraction data acquisition. This allowed to reach with HRFD extremely high resolution (Δd/d ≈ 0.001) over a wide range of inter-planar spacings at a relatively short flight path between chopper and sample (L = 20 m). Over time, a lot of diffraction experiments on crystalline materials, the main goal of which was to study their atomic and magnetic structures, were performed at HRFD. Successful implementation of the Fourier diffractometry technique at the IBR-2 reactor stimulated the construction of yet another Fourier diffractometer intended for internal mechanical stress studies in bulk materials (FSD, Fourier Stress Diffractometer). In this paper the experience of using this technique at the IBR-2, which is a long-pulse neutron source, is considered, the examples of HRFD studies are given, and possible solutions for existing technical problems of using correlation diffractometry and ways of increasing the intensity and resolution of HRFD are discussed.

Neutron diffraction investigations of residual stresses around a zirconium-stainless steel interface in a bimetallic adapter

This paper presents the results of neutron diffraction investigations of the residual stress state around a zirconium-stainless steel interface in a bimetallic adapter used for some channels in RBMK-type reactors. The adapter consists of a cylinder with a complex cross section with an outer stainless steel layer and an inner zirconium layer. The experiments are carried out on a Pulse overlap time-of-flight diffractometer (POLDI, SINQ) (Paul Scherrer Institut, Switzerland), a Fourier stress diffractometer (FSD), and high resolution Fourier diffractometer (HRFD) at the IBR-2 pulsed reactor (Frank Laboratory of Neutron Physics, JINR, Dubna, Russia).

Crystal structure phase separation in anion-deficient La0.70Sr0.30MnO3 − δ manganite system

The crystal structure of anion-deficient La0.70Sr0.30MnO3 − δ manganite powders (δ = 0, 0.10, 0.15, 0.20) has been investigated at room temperature by the neutron diffraction method using a high-resolution Fourier diffractometer. The structure data have been refined by the Rietveld method. The crystal structures of the stoichiometric La0.70Sr0.30MnO3 and anion-deficient La0.70Sr0.30MnO2.90 manganites are satisfactorily described by the rhombohedral space group R\(\bar 3\)c. A small amount of the non-perovskite MnO phase (space group Fm\(\bar 3\)m) has been found for the anion-deficient La0.70Sr0.30MnO2.90 sample. It has been found that the anion-deficient La0.70Sr0.30MnO2.85 sample consists of two perovskite phases described by space groups R\(\bar 3\)c and I4/mcm and the MnO phase (space group Fm\(\bar 3\)m). The crystal structure of the anion-deficient La0.70Sr0.30MnO2.80 sample is described by one perovskite phase with space group I4/mcm. The volume fraction of the MnO phase is ≪1% for all anion-deficient samples. Oxygen vacancies in the anion-deficient La0.70Sr0.30MnO3 − δ manganite system stimulate the structure phase separation at 293 K.

Investigation of Residual Stresses in a Bimetallic Stainless Steel-Zirconium Adapter by Neutron Diffraction

In this paper we present the results of residual stress measurements in a bimetallic stainless steel –zirconium adapter, which is used in some structures of RBMK reactor channels. The stresses in this component arise due to various manufacturing processes and the thermal expansion factor mismatch between the two alloys. The residual stress distribution in stainless steel was investigated. The residual stresses on three different cross sections were measured. The experiments were carried out on High Resolution Fourier Diffractometer (HRFD) and Fourier stress Diffractometer (FSD) at the pulsed reactor IBR-2 (Dubna, Russia) and on the high-resolution neutron diffractometer at power reactor LVR 15 (NPI, Rez, Czech Republic).

Neutron Fourier diffractometer FSD for internal stress analysis: first results

At the IBR-2 pulsed reactor in Dubna a new neutron Fourier diffractometer FSD is under construction. FSD continues the development of neutron Fourier diffractometry at long-pulse neutron sources, which was started several years ago with the high-resolution Fourier diffractometer HRFD at the IBR-2. Whereas HRFD is mainly used for precise structural refinement, FSD is optimised for internal stress measurements in bulk materials. The FSD design satisfies the requirements of high luminosity, high resolution, a specific sample environment, a wide range of dhkl, and fixed scattering angles 2θ=±90°. It consists of a mirror neutron guide, a fast Fourier chopper for the neutron-beam intensity modulation, a ±90° MultiCon ZnS(Ag) 6Li-loaded detector system with both geometrical and electronic focusing, a five-axis goniometer ‘Huber’ and loading machines, and VME-based RTOF analysers for data acquisition. Examples of the first experimental results obtained with FSD are presented.

Determination of Residual Stresses in WCu Gradient Materials

Residual stress measurements were carried out on copper–tungsten gradient materials by means of neutron diffraction on the High Resolution Fourier Diffractometer on IBR-2, JINR, Dubna. The samples so far investigated had a concentration profile that approximates the gradient by step functions. The results show an averaged positive stress (stretch) in the copper phase and negative (compression) in the tungsten phase. A comparison to analytical linear elastic calculations shows that the measured values are nearly an order of magnitude too low, whereas however, a qualitative agreement of the stress distribution exists. That this quantitative discrepancy can be attributed to the model's simplifying assumption of pure elastic behaviour can be shown by recent calculations that also include plasticity and show a much better agreement with the experimental values. Single peak evaluation also strongly suggests that plasticity does indeed play a significant role.

A multi-DSP system for the neutron high resolution Fourier diffractometer

The multi-DSP data acquisition system for neutron time-of-flight spectrum measurements requiring fast real-time data processing is designed and is operated at the neutron High Resolution Fourier Diffractometer (HRFD). The use of high performance DSPs and front-end electronics based on flexible PLDs allows increasing of the efficiency of neutron diffractometers with a Fourier chopper and a multi-element detector system by the method of electronic time-focusing.

High-resolution Fourier diffractometry for long-pulse neutron sources

New ideas and novel electronics have renewed the interest in neutron scattering correlation technique which has become popular again after a long period of disregard. In this paper, application of the correlation Fourier technique to diffraction experiments at long-pulse neutron sources (LPS) and the experience of operating the high resolution Fourier diffractometer (HRFD) instrument, the first neutron HRFD at the LPS-type source, the IBR-2 pulsed reactor in Dubna, are discussed. A comparison between the performance parameters of conventional time-of-flight (TOF)-diffractometers at LPS with the possible characteristics of the Fourier diffractometer is presented.

Performance of the high resolution fourier diffractometer at the IBR-2 pulsed reactor

Abstract The first neutron Fourier diffractometer at the pulsed neutron source, the High Resolution Fourier Diffractometer (HRFD), is described. The HRFD combines both high neutron flux at the sample position, ∼107n/cm2/s, provided by the IBR-2 high flux pulsed reactor, and high resolution, very close to 0.001, over a wide range of d-spacings. The paper deals with the basic principles of HRFD, its design, and performance. Examples of structural experiments are also given.

Equipment for Residual Stress Measurements with the High Resolution Fourier Diffractometer: Present Status and Prospects

Equipment for Residual Stress Measurements with the High Resolution Fourier Diffractometer: Present Status and Prospects