High-resolution Neutron Powder Diffractometer Research Articles

HRPD and TEM Study of P/M 58Fe17Cr25Ni Austenitic Stainless Steel Synthesized by Spark Plasma Sintering

58Fe17Cr25Ni austenite stainless steel has been fabricated using metal powder through sintering with a spark plasma at temperatures of 900 and 950°C for 5 minutes. High purity Fe, Ni and Cr powders were used as materials for this steel. Before sintering, the powder was mixed in a milling equipment which was processed for 5 hours, then it is formed into a coin by pressing it under a load of 25 tons. High resolution powder neutron diffractometer was used for identifying the crystal structure in the 58Fe17Cr25Ni austenitic stainless steel. The sintering process at temperatures of 900C and 950°C generally forms microstructure having matrix of equiaxed austenite grains, with a crystal structure of face-centered cubic which included in the Fm3m space group. Some particles with high Cr content, a'-Cr, are distributed in all austenite grains. The austenite grains seen in the 58Fe17Cr25Niaustenitic stainless steel sintered at 900°C are twin grains. Dislocations, slip planes and bands are also existed in those grains. These defects are expected to decrease with increasing sintering temperatures up to 950° C. This change was followed by the appearance of air bubbles and sub-grains as the dominant sub-structures in the 58Fe17Cr25Ni austenitic stainless steel sintered at 950°C.

Upgrade of Xuanwu: A dual-mode neutron powder diffractometer at CMRR

Neutron diffraction (ND) is a well-established technique of great significance in condensed physics and materials science. Although it has particular advantages against its brother X-ray diffraction (XRD), intensity is still a limiting factor counteracting its application. Herein, we report the upgrade of Xuanwu, a high-resolution neutron powder diffractometer at the China Mianyang Research Reactor (CMRR). A doubly focusing monochromator system made of Si blades is applied to enhance the intensity from 2 × 105n⋅cm−2⋅s−1 to 2.39 × 106n⋅cm−2⋅s−1 with changeable wavelength. The high-resolution mode with a best resolution 1.6‰ is reserved, which means the working style is optional between high-resolution and high-intensity, making Xuanwu more applicable in expanded scopes.

Effects of Plasma Sintering on the Post TIG Weld Joint of Fe-15Cr-25Ni Austenitic Stainless Steel

Arc-plasma sintering (APS) for 5 s has been applied to the post tungsten inert gas (TIG) weld joint of Fe–15Cr–25Ni austenitic stainless steel (ASS). The treatment is intended to observe the effect of heat generated by plasma on micro-crystal structures around the fusion zone (FZ), especially internal stress relief in steel after being subjected to welding. The effect of stress relief in weld was measured using the neutron diffraction technique. ASS that is predominantly composed of Fe, Cr, and Ni elements, with contents of 57%, 15%, and 25%wt. respectively, was cut into two parts. Both parts were then welded with TIG without filler with a current and voltage of 60 A and 50 V, respectively. After APS for 5 s, the sample was characterized and analyzed using high-resolution powder neutron diffractometer at a high-temperature laboratory facility. The results show that the tensile residual stress decreased with the APS heat input. The residual stresses significantly decreased from 82.40 MPa to 1.21 MPa in the FZ and continued almost evenly from 65.92 MPa to 1.24 MPa in the heat-affected zone (HAZ). The residual stress is a tensile stress that can reduce the mechanical strength of materials. This condition is also applicable to applied loads. A microstructure gives a confirmation that the C element migrates from the FZ to HAZ. The content was very high in dark traces. The C element reacts to Cr and O to form chromium carbide (Cr23C6) and chromium carbonyl (CrC6O6), respectively. It rapidly migrates among its grain boundaries. It may also weaken materials and probably initiate intergranular cracks.

Neutron Diffraction Study on Ce-Doped Nickel Ferrite Nanoparticles

The NiCexFe2-xO4 polycrystalline spinel compound with composition x = 0.005, 0.010, 0.015, and 0.02 was synthesized by the solid reaction method using the high energy milling (HEM) apparatus. Measurement of the neutron diffraction patterns is carried out at room temperature using a high resolution powder neutron diffractometer (HRPD), wavelength λ = 1.8213 Å. The measured neutron diffraction data were analyzed by the Rietveld method utilizing the FullProf analysis code. The results of the neutron diffraction pattern refinement revealed that the sample has a cubic symmetry, the Fd-3m space group, mixed inverse spinel structure, A-site occupied by cation Fe3+, Ni2+, dan Ce3+. Whereas the B-site is only occupied by Fe3+ and Ni2+. The mole fraction of Fe3+ at the B-site is greater than the Fe3+ mole fraction at the A-site, whereas the mole fraction of Ni2+ at the B-site is smaller than the mole fraction of Ni2+ at the B-site. As a result of Ce3+ doping, oxygen position parameters increase, magnetic moments on B-site, and the net magnetic moments decrease. Ni2+ concentrations at the A-site and the B-site were not affected by the amount of Ce3+ substitutions. Without substitution and after Ce3+ substitution, the O-site occupancy factor is still oxygen deficient.

Neutron Guide Building instruments of the Brazilian Multipurpose Reactor (RMB) project

A growing community of scientists has been using neutrons in the most diverse areas of science. In order to meet the researchers demand in the areas of physics, chemistry, materials sciences, engineering, cultural heritage, biology and earth sciences, the Brazilian Multipurpose Reactor (RMB) will provide 3 thermal guides and 3 cold guides, with the installation of several instruments for materials characterization. In this study, we present a standard design requirement of two primordial instruments, namely Sabi'a and Araponga. They are, respectively, cold and thermal neutron instruments and correspond to a Small-Angle Neutron Scattering (SANS) and High-Resolution Powder Neutron Diffractometer (HRPND) to be installed in the Neutron Guide Building (N02) of RMB . To provide adequate flux for both instruments, we propose here an initial investigation of the use of simple and split guides to transport neutron beams to two different instruments on the same guide. For this purpose, we use Monte Carlo simulations utilizing McStas software to check the efficiency of thermal neutron transport for different basic configuration and sources. By considering these results, it is possible to conclude that the split guide configuration is, in most cases, more efficient than cases that use transmitted neutron beams independently of source. We also verify that the employment of different coating indexes for concave and convex surfaces on curved guides is crucial, at least on simulated cases, to optimise neutron flux (intensity and divergence) and diminish facility installation cost.

Neutron Diffraction Study of Multiferroic 0.6NiFe2O4/0.4BaTiO3 Composite

Neutron diffraction study on the 0.6NiFe2O4/0.4BaTiO3 multiferroic composite has been carried out. The 0.6NiFe2O4/0.4BaTiO3 multiferroic composites have been synthesized by solid reaction method. In this study, 20 g of BaTiO3 (BTO) and 20 g of NiFe2O4 (NFO) compounds were prepared from the powder raw materials of BaO3 and TiO2 for BTO, and NiO and Fe2O3 for NFO. Furthermore, both BTO and NFO were each crushed for 5 hours using High Energy Milling (HEM). Then the BTO and NFO were calcined in the furnace at 950°C/5 hours and 900°C/5 hours, respectively. Both NFO and BTO precursors were manually mixed with a weight percent ratio of NFO:BTO was 100:0, 60:40, and 0:100, hereinafter referred to NFO, NFO/BTO, and BTO, respectively. Then the three samples were pressed into pellets. The pellets were then sintered at 1150 °C/5 hours with a heating rate of about 44.8°C/min. Once cooled to room temperature within the furnace it was obtained NFO, BTO, and NFO/BTO multiferroic composite. The magnetic properties of the material were observed with the aid of the Vibrating Sample Magnetometer (VSM) instrument. The nuclear structure of BTO, and the magnetic structure of NFO, and NFO/BTO multiferroic composite were determined by neutron diffraction technique using the high resolution powder neutron diffractometer. The cations arrangement of NFO was obtained by whole pattern fitting with the Rietveld method based on neutron diffraction data using FullProf software. The cations arrangement was obtained by refining the occupancy of individual cation at tetrahedral and octahedral sites. The results of the analysis show that both NFO and 0.6NFO/0.4BTO samples have a mixed spinel structure, it means that there are cations of Ni2+ and Fe3+ on A-site and B-site. In NFO sample, the cations distribution among the A-site and B-site of NiFe2O4 is [Ni0.002Fe0.852][Ni0.006Fe0.862]2O4. The cations distribution among the A-site and B-site of NiFe2O4 in 0.6NFO/0.4BTO samples is [Ni0.0250Fe0.8975] [Ni0.012Fe0.950]2O4. So, the effect of adding BTO as a composite is to increase Ni2+ occupancy by 12.5 times on A-site and 2 times on B-site. The magnetic moment of multiferroic 0.6NFO/0.4BTO composite is 2.4(5) µB same as one of NFO. The BTO content in the composite has caused tensile strains induced into the NFO lattice, and at the same time, tensile strains of NFO caused the compressive strain on the c lattice of BTO even though the unit cell volume of BTO is also increasing from 64.100(5) to 64.374(6) A3.

Weak Ferromagnetic Property and Electromagnetic Waves Absorption Characteristic of La(1-x)BaxMnO3

The weak ferromagnetic property and the electromagnetic waves absorption characteristic of La(1-x)BaxMnO3 (LBMO) compounds have been investigated. The samples of LBMO that are LaMnO3 (S0), La0.9Ba0.1MnO3 (S1); La0.8Ba0.2MnO3 (S2); and La0.7Ba0.3MnO3 (S3) were synthesized using high energy milling (HEM) method. Samples were characterized by means of XRD (X-ray diffractometer), HRPD (high-resolution powder neutron diffractometer), EDS (energy dispersive X-ray spectroscopy, VSM (vibrating sample magnetometer), and VNA (vector network analyzer). There is no magnetic ordering of ferromagnetic in S1 and S2 samples due to the Ba occupation factors of both less than 0.2. The Ba content in the S3 sample is greater than 0.2, hence the ferromagnetic property of the compound is not so visible with the VSM as well as the VNA. The absorption characteristics of electromagnetic waves using VNA indicated that there is an absorption of EM waves in the frequency range between 8-12 GHz with almost the same peak frequency for all four samples at 10.8 GHz with the absorption of around 5 dB. The existence of a weak ferromagnetic property can be detected clearly using HRPD. Neutron diffraction as a probe can observe the magnetic structure accurately even in a material having a weak ferromagnetic property.

ECHIDNA: a decade of high-resolution neutron powder diffraction at OPAL

The ECHIDNA high-resolution neutron powder diffractometer at the 20 MW OPAL research reactor in Australia produces high-quality data for a broad spectrum of crystal and magnetic structural studies. The paper presents an overview of the current status of the hardware, latest developments in data-reduction software, statistics on instrument usage and the user programme, and instrument limitations.

Magnetic Structure of Magnetite Phase of Iron Sand Retrieved from Banten, Indonesia

Among the many types of natural resources that are abundant in Indonesia is iron sand. One of the products of the iron sand processing is magnetite (Fe3O4). The stages of separation and purification process that has been done before were extracting magnetite phase and discarding the other phases. Magnetic structure of magnetite phase of iron sand retrieved from Banten, Indonesia has been invesigated. The aims of this research is to analyze the structure of the new magnetite phase, FexMyO4. The magnetic properties of the sample was evaluated by means of vibrating sample magnetometer (VSM). Sample characterizations was carried out by neutron activation analysis (NAA) method. The analysis result from NAA shows that there are still 17 impurities remaining, namely: M = Ti, Al, Ce, Co, Cr, Eu, La, Mg, Mn, Na, Sc, Sm, Th, V, Yb and Zn, and there are about 94% of iron sites are filled by Fe elements. The structural analysis was carried out by the help of the high resolution neutron powder diffractometer (HRPD) using a wavelength of λ = 1.8223 Å. Neutron diffraction data was analyzed by means of FullProf software. The analysis result shows that the sample hasthe chemical formula: (Fe0.97M0.03)3O4 with a cubic crystal system, space group: Fd-3m and lattice parameters: a = b = c = 8.36834 (3) Å, α = β = γ = 90°. The sample is magnetic at room temperature because the compound has a net magnetic moment, μ = 2.9(1) μB. The magnetic moments of the sample is lower than the magnetic moments of pure Fe3O4 (μ = 3.8 μB), because of about 3% of Fe sites are occupied by impurity elements. Magnetic properties of magnetite phase depend on the purity of the magnetite phase.

Crystal Structure Investigation of Ferritic 73Fe24Cr2Si0.8Mn0.1Ni Steel for Multi-purpose Structural Material Applications

Microstructural identification of synthesized steel with significant local content has been carried out. Alloy ingot was prepared using a casting technique. The samples were then formed into bulk steel by a machining process. A high resolution powder neutron diffractometer (HRPD) was used as an equipment for characterization. By applying neutron diffraction techniques, a ferritic steel profile can be resulted in as well as ‘minor peaks’ belong to impurities formed in the sample. These impurities can be identified as small amounts of Al2O3 54SiO2, Al4C3, SiC and Cr23C6. Scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDX) confirmed and revealed neutron identified phase distributions. Joint Committee on Powder Diffraction Standards (JCPDS) least square curves calibration can precisely calculate the dhkl parameters of each reflection plane. As a comparison, another sample of alloy ingot was also investigated using neutron diffraction. The pattern was free from crystal impurities. Rietveld refinements provide satisfactory goodness of fits Rwp = 10.42% and reliability factor S = 1.7. This was so-called a ‘real bulky’ sample of a 73Fe24Cr2Si0.8Mn0.1Ni ferritic steel alloy.

The investigation of magnetic phase transition in cobaltite perovskites by high-resolution neutron powder diffraction under 14 T magnetic field

We carried out neutron powder diffraction (NPD) experiments on the layered perovskite cobaltite PrBaCo2O5.5+x (x = 0.24) at Super High Resolution Neutron Powder Diffractometer (SuperHRPD) with a newly installed magnet. At low temperatures, the antiferromagnetic (AFM) reflections of the NPD profile are suppressed whilst ferromagnetic (FM) reflections are enhanced under 14 T magnetic field. The magnetic-field-induced AFM-FM transition reveals the ground-state energy of FM is close to that of AFM.

Weak-ferromagnetism of CoF3 and FeF3

Cobalt trifluoride CoF3 and Iron trifluoride FeF3 are known as a G-type antiferromagnetic structure in the R-3c rhombohedral crystal structure. The neutron powder diffraction study had been reported that Co antiferromagnetic spin direction is parallel to 3-fold crystal axis in CoF3 whereas Fe antiferromagnetic spin direction is perpendicular to 3-fold crystal axis in FeF3. However, the resolution of early neutron powder diffractometer is not enough to distinguish between (003)h and (101)h rhombohedral magnetic peaks definitely.We employed high-resolution powder neutron diffractometer(SuperHRPD) at room temperature in MLF, J-PARC. The time-of-flight neutron powder diffractometer distinguishes clearly between (003)h and (101)h magnetic peaks. Then, we confirmed the proposed magnetic structural models of CoF3 and FeF3 at room temperature. In a magnetic susceptibility, CoF3 displays the additional magnetic anomaly at T* = 40 K. We discussed possible weak-ferromagnetism by the interplay of spin tilting and Dzyaloshinski-Moriya interactions.

Magnetoelastic coupling forbidden by time-reversal symmetry: Spin-direction-dependent magnetoelastic coupling on MnO, CoO, and NiO

In the Landau free energy, which is a powerful tool for describing the physical properties and phase transitions in condensed-matter physics, it has been generally believed that time-reversal symmetry allows only even-power polynomials in the magnetic moment when magnetic transition happens. Although no experimental evidence supports it, this symmetry constraint is very strict in theory. On the other hand, MnO, CoO, and NiO have been extensively studied for several decades since these materials are used to test advance experimental and theoretical methods. However, their precise spin directions and phase-transition mechanism have remained as a long-standing problem until now. To resolve these issues, we used the cutting-edge time-of-flight neutron powder diffractometer (SuperHRPD) at the Japan Proton Accelerator Research Complex (J-PARC) to study the spin-direction-dependent magnetoelastic coupling in MnO, CoO, and NiO. We also constructed a group-subgroup structure relation from $Fm\ensuremath{-}3m$ to $C2/m$ with exchange striction and a type of magnetostriction (dipolar and roto magnetostriction). These unified viewpoints and the high-resolution neutron powder diffractometer enable us to construct an order-parameter vector diagram. The order-parameter vector diagram reveals distinguished order-parameter coupling and phase-transition characters by different ${\mathrm{\ensuremath{\Gamma}}}_{1}^{+}({A}_{g})$ and ${\mathrm{\ensuremath{\Gamma}}}_{2}^{+}({B}_{g})$ spin direction. Moreover, the experiment results show clearly that the ${\mathrm{CoO}}_{6}$ octahedral distortion and the Co magnetic moment couple through a magnetoelastic coupling ${\ensuremath{\epsilon}}_{\text{oct}}\ensuremath{\sim}{M}^{3}$, which is forbidden by time-reversal symmetry but allowed by the more general magnetic symmetry---the so-called rotation-time-reversal symmetry in the double antisymmetry space group. Rotation-time-reversal symmetry allows the coupling of odd-power polynomials in the spin vector and odd-power ones in the roto vector when both spin- and roto-axial vectors belong to the same irreducible representation in Landau free energy. Here, we show experimental evidence that the magnetic order parameter and static structural order parameter belong to the same irreducible representation in the materials. Experimental discovery of general magnetic symmetry opens a way to find the physics forbidden by time-reversal symmetry in condensed matter physics.

Monoclinic ferroelectric NaNbO3 at room temperature: Crystal structure solved by using super high resolution neutron powder diffraction

The crystal structure of NaNbO3 at ambient temperature was solved using time-off-flight neutron data obtained from Super High Resolution Neutron Powder Diffractometer in J-PARC. The solved structure was a novel monoclinic type with the space group Pm and lattice parameters of a=5.50453(1), b=15.52975(3), c=5.56779(1)Å, and β=90.0645(2)°. Bond valence calculation indicates that the solved structure is chemically valid. This solved structure corresponds with the observed ferroelectric behaviors (Ps=11–25μC/cm2, S=0.03–0.04%). The calculated Ps (~21μC/cm2) using the refined atomic parameters for one-quarter unit cell conform well to the observed value. Cooperative NbO6 octahedral tilting accompanied by the phase transition from the parent structure Pcmb to the Pm mainly contributes to the spontaneous polarization.

Detailed Study of the Phase Diagram of Fe-based Superconductor Ba(Fe1-xCox)2As2 by Super High-Resolution Neutron Diffraction Measurements

Temperature (T) dependence of Bragg reflections of Ba(Fe1-xCox)2As2 (x = 0, 0.02) have been measured in detail on assembled mm-size crystallites to avoid effects of surface and/or externally induced strains with the high-resolution neutron powder diffractometer, where we have found that the profile width of the (400)O/(040)O reflections with the orthorhombic indexing begin to increase, as T decreases, at ~270 K, much higher than the tetragonal (Tet)-orthorhombic (Ort) second order transition temperature TS (-147.5 K) without showing any indication of an phase change above TS. The coexistence of two Ort phases with different orthorhombicity exists in the region of ~140 K < T < 143 K). The profile widths of (hhl)O reflections are nearly T-independent in the entire temperature region studied here (130 K ≤ T ≤ 350 K). An additional broadening due to the Co-doping is clearly found. We discuss these results in relation to the breakdown of the 4-fold symmetry of static physical quantities found in the electrical resistivity and band splitting of the 3dyz and 3dzx and orbitals and conclude that the disappearance of the 4-fold symmetry even in the macroscopically tetragonal phase can be understood by the existence of orthorhombic domains induced by crystal defects and/or impurities.

Neutron diffraction investigation of phase compositions in as received and modified Zr–2·5Nb pressure tube materials

Zr–2·5Nb alloy is used for the pressure tubes in CANDU [CANDU® (CANada Deuterium Uranium) is a registered trademark of Atomic Energy of Canada Limited.] reactor fuel channels. Three phases (α, β and ω) of zirconium are known to exist in Zr–2·5Nb alloy pressure tube materials. An as received pressure tube is composed mainly of α phase and approximately 8% β phase material. In the last step of production, the pressure tube is given a steam autoclave treatment (i.e. thermal aging at 400°C for 24 h). This treatment results in decomposing the β phase into an Nb enriched β phase and a metastable ω phase material. In the present experiment, as received pressure tube materials were modified by high temperature annealing and thermal aging treatments. This paper presents a neutron diffraction investigation into the phase compositions in the modified materials at room temperature using the C-2 high resolution neutron powder diffractometer at the Canadian Neutron Beam Centre.

Neutron diffraction on functional materials under electric field or mech. load

In this contribution neutron diffraction studies on functional materials under special environmenal conditions will be presented. In particular, studies of ferroelectric ceramics under high electric fields as well as shape memory alloys under mechanical load will be highlighted. The investigations were carried out at the high-resolution neutron powder diffractometer SPODI (FRM II / Garching n. Munich) which offers special sample environmenal tools for electric fields, mechanical load etc. In-situ studies on ferroelectrics under the influence of high electric fields enable to establish correlations between the macroscopic poling behaviour and corresponding structural changes. The investigations were carried out on technologically applied lead zirconate titanate based samples and on a bismuth sodium titanate based system. A self-designed device allows the investigation of large bulk samples under different orientations of the electric field. This method allows to analyze the poling mechanisms in technical ferroelectrics, such as piezoelectric effect, domain reorientation and phase transformations. In the system Bi0.5Na0.5TiO3 - BaTiO3 – K0.5Na0.5NbO3 the large recoverable field-induced strain could be attributed to a reversible field-induced phase transition from an almost non-polar, pseudocubic tetragonal phase to a distorted, ferroelectric active phase [1]. Polycristalline monoclinic nickel-titanium shape memory alloys have been investigated under mechanical load to analyze their stress-strain behaviour and to derive the elastic constants. A novel tensile rig allows to orient the load axis in a Eulerian cradle like manner. The elastic constants tensor could be calculated based on a series of diffraction patterns under different sample orientations in the initial state and under 0.6 % strain. Furthermore the contributions of elastic deformation (lattice dilatation) and inelastic deformation (orentation of twins) to the total strain could be separated.

High-resolution neutron powder diffractometer SPODI at research reactor FRM II

SPODI is a high-resolution thermal neutron diffractometer at the research reactor Heinz Maier-Leibnitz (FRM II) especially dedicated to structural studies of complex systems. Unique features like a very large monochromator take-off angle of 155° and a 5 m monochromator–sample distance in its standard configuration achieve both high-resolution and a good profile shape for a broad scattering angle range. Two dimensional data are collected by an array of 80 vertical position sensitive 3He detectors. SPODI is well suited for studies of complex structural and magnetic order and disorder phenomena at non-ambient conditions. In addition to standard sample environment facilities (cryostats, furnaces, magnet) specific devices (rotatable load frame, cell for electric fields, multichannel potentiostat) were developed. Thus the characterisation of functional materials at in-operando conditions can be achieved. In this contribution the details of the design and present performance of the instrument are reported along with its specifications. A new concept for data reduction using a 2 θ dependent variable height for the intensity integration along the Debye–Scherrer lines is introduced.

Recent developments at the ECHIDNA high-resolution neutron powder diffractometer

Recent developments at the ECHIDNA high-resolution neutron powder diffractometer

Compositionally driven ferroelectric phase transition in xBiInO3–(1−x)BaTiO3: a lead-free perovskite-based piezoelectric material

A comprehensive structural investigation has been carried out on xBiInO(3)-(1-x)BaTiO3, where x <= 0.25, using the high resolution neutron powder diffractometer D2B at Institut Laue-Langevin, France. The room temperature structures of eight different compositions between x=0.03 and 0.25 of this solid solution have been determined through Rietveld refinement. A gradual structural phase transition has been observed as a function of composition, where the tetragonal (P4mm) structure (ferroelectric phase) has transformed into a cubic (Pm (3) over barm) structure (paraelectric phase) after passing through a region of coexisting phases. Details of the crystallographic information obtained from the refinement have been presented. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3442504]