High-resolution Powder Diffractometer Research Articles

Magnetic field induced phase transition in Ce 2 Fe 17-x Mn x compounds

The atomic and magnetic structures of Ce2Fe17−xMnx compounds with x = 0.5 and 1.0 were inves- tigated using neutron diffraction under magnetic fields up to 5.0 T over the temperature range 2 − 300 K. The magnetic reflexes observed at temperatures 2 − 208 K and µ0 H = 0T correspond to an incommensurate antiferromagnetic struc- ture with wave vector (0, 0, 0 ± τ) at 2 K. This structure is suppressed in an external magnetic field and a ferromagnetic phase is induced in fields higher than 0.6 T. The complex transformation of the magnetic structures under magnetic field and temperature is analyzed and discussed. 1 Experimental methods Polycrystalline samples of Ce2Fe17−x Mnx with x = 0. 5a nd 1.0 were prepared by high-frequency melting under argon at- mosphere in Al2O3 crucibles. The ingots were annealed under vacuum at 1173 K for 3 days and then quenched in water. X-ray diffraction at room temperature with CuKα radiation was employed to test the structure and the lattice parame- ters. Neutron-diffraction experiments were performed at the high-flux reactor of the ILL. The high-resolution D2B and D1A powder diffractometers were used for a detailed study of the crystal structure at selected temperatures. The high- intensity powder diffractometer D1B was used for thermal scans under magnetic fields up to 1.2 T using a wavelength of 2.524 A and covering an angular range from 2 up to 82 degrees in 2Θ. In all cases the neutron diffraction data refine- ment was performed using the Rietveld method by means of the FULLPROF program.

Residual stress instrument at the HANARO

A residual stress instrument was developed and measurement service has been available since early 2000 at the HANARO. The instrument is an optional instrument to a high-resolution powder diffractometer sharing its sample table and monochromator with changeable optical components and a linear position-sensitive detector unit. We report here the installation of the residual stress instrument at the HANARO and its early measurements on the samples of VAMAS and some engineering components. A short description of future plans is also included.

Assessment of preferred orientation with neutron powder diffraction data

Crystallographic texture (or preferred orientation) characterization of uniaxially pressed molybdite (MoO3) and calcite (CaCO3) powders has been carried out using the BT-1 high-resolution fixed-wavelength 32-detector powder diffractometer at the NIST Center for Neutron Research. Initially, each pattern was analysed assuming a random orientation of the crystallites. Subsequently, the March model and the generalized spherical harmonic description were used independently to extract the texture description directly from a refinement with neutron diffraction data of molybdite and calcite. The results indicate that the generalized spherical harmonic description provided a better Rietveld fit than the March model for the molybdite sample that had been subjected to the highest pressure.

Residual Thermal Phase Stresses in α-γ Fe-Cr-Ni Alloys Measured by a Neutron Diffraction Time-of-Flight Method

Residual thermal phase elastic strains in rod specimens and powders with particle size from 150 to 250 \\micron of α-γ Fe–Cr–Ni alloys quenched from 1273 to 273 K, were measured by means of a high-resolution neutron powder diffractometer using a time-of-flight (TOF) method. Diffraction patterns were analyzed by the Rietveld method and the single-peak method. Residual thermal phase strains obtained in the rod specimens or the powders from the both methods are positive, i.e., tensile, for austenite (γ) phase and negative for ferrite (α) phase, being consistent with the prediction from the difference in thermal expansion coefficients of the constituent phases. The Rietveld analysis combined with the TOF method is considered to give the most reliable results of the average thermal phase strain. The results by the single-peak analysis suggest that thermal phase strain shows [hkl] dependence; the absolute value of thermal phase strain is decreased with increasing of the Young modulus along the [hkl] direction.

Synchrotron strain scanning on BM16 at the ESRF

BM16 is a high-resolution X-ray powder diffractometer, with an energy range 5–40 keV (2.5–0.3 Å), situated on a bending magnet source at the ESRF, Grenoble. At the higher energies it is possible to penetrate through lighter element materials without

Research and facility of neutron scattering in Indonesia

Neutron scattering activities in Indonesia during last fiscal year are reported in this paper. The neutron beam facilities in Serpong include one diffractometer (DN1-M) for residual stress measurements, one diffractometer (FCD/TD) for single-crystal structure determinations and texture measurements, one high resolution powder diffractometer (HRPD), one neutron radiography facility (NRF), one triple axis spectrometer (TAS), one small angle neutron scattering spectrometer (SANS) and one high-resolution small-angle neutron scattering spectrometer (HRSANS). Four instruments related to this symposium among them are discussed. The FCD/TD, HRSANS and TAS are not working now because of some electronic troubles. NRF is working but not at its best condition. The HRPD, DN1-M and SANS are running well, and HRPD is used heavily. The latest situation of the reactor and its operation mode are also described briefly in connection with activities of the neutron scattering instruments.

E9: The New High-Resolution Neutron Powder Diffractometer at the Berlin Neutron Scattering Center

E9: The New High-Resolution Neutron Powder Diffractometer at the Berlin Neutron Scattering Center

E9: The new high-resolution powder diffractometer at BENSC

In the past only powder diffractometers with medium resolution were available at BENSC. To satisfy ademand from the user community for crystal structure refinements using the Rierveld method, a new high-resolution powder diffractometer has been installed at the BER2 reactor and it came into user operation during the second half of 1999. The instrument is designed for investigating crystal structures with cell volumes up to 1000 k3 by profile refinements of powder diffractograms. Data sets of sufficient resolution and statistics depenlng on the complexity of the structure are needed to apply the Rietveld method successfully. To fulfill these demands, it was decided to build an instrument based on a classical angular dispersive diffractometer similar to the D2B at the ILL however, with relaxed collimations considering the lower thermal flux at the BER2 compared to the ILL reactor. Beside the standard setting with a take-off angle at the monochromator above 90°, the instrument allows to vary the take-off angle in a large angular range. In combination with the optional use of different reflecting planes of the Ge-monochromator crystals, the diffractometer exhibits a great flexibility in the choice of wavelength and resolution. In the following we willshortly describe the instrument design and list the important instrumental specifications. In particular we will describe the performance of the instrument and focus on the line profile shapes, which are crucial for the quality of the Rietveld refinement. Finally an example is presented which illustrates the possibilities the instrument off ersfor crystal structure refinements.

X-ray diffraction line broadening from thermally deposited gold films

Diffraction profiles were analysed from thermally deposited 111-oriented gold films, ranging in thickness from 300 to 1900 Å. The data were collected using the high-resolution powder diffractometer on beamline BM16 at the European Synchrotron Research Facility (ESRF) set at a wavelength of 0.3507 Å. The profiles were measured under conventional symmetric θ–2θ reflection conditions and by asymmetric transmission diffraction to ensure that only crystallites oriented normal to the substrate contribute to the diffraction. An analysis of the instrument profile shape of the diffractometer was undertaken using the SRM 660 LaB6line profile standard. A parallel study of the films using atomic force microscopy and transmission electron microscopy was also undertaken to provide information on the dimensions of the crystallite columns in the films and the presence of dislocations. All the films displayed diffraction broadening arising from both crystallite-size effects and dislocation-induced strain effects. Analysis of the magnitude and anisotropy of the dislocation-induced broadening withhklindicates that the dislocations have a mixed screw/edge character and tend to form primarily on (111) slip planes parallel to the substrate at densities of ∼1015to 1016 m−2.

Neutron diffraction study on hydrogen bond structure inK3H(SeO4)2 and K3D(SeO4)2 crystals

Neutron diffraction experiments on the room- and low-temperature phases ofK3H(SeO4)2 (Ttrs = 21 K) and K3D(SeO4)2 (Ttrs = 105 K)have been performed using the time-of-flight high-resolution powderdiffractometer HRPD at the ISIS pulsed neutron source. Data were collected at 2and 30 K for K3H(SeO4)2 and 2 and 130 K for K3D(SeO4)2 overthe d-spacing range 0.7-2.4 Å. The room-temperature phases of the crystalshave monoclinic structure belonging to the space group A2/a. Rietveldrefinement combined with the published dielectric and calorimetric studiesreveals that H/D atoms are disordered over two symmetry-equivalentpositions. The hydrogen bonds are non-linear with an O-H/D···O angleof 175(1)°. The hydrogen bond length is 2.495(1) Å inK3H(SeO4)2 and 2.533(2) Å in K3D(SeO4)2. The separationbetween the half occupancy hydrogen positions is 0.32(1) Å forK3H(SeO4)2 and 0.550(4) Å for K3D(SeO4)2. The relationbetween these structural parameters and the isotope effect in the transitiontemperature is discussed. Diffraction patterns of the low-temperature phasesindicated that the structure change accompanying the transition is very small.

High-resolution powder diffractometer HRPT for thermal neutrons at SINQ

Design characteristics and first experience concerning the new high-resolution powder diffractometer for thermal neutrons at the Swiss spallation neutron source SINQ are summarized. It is based on a linear position-sensitive 3 He detector with 1600 wires and angular separation of 0.1°, permitting also real-time experiments.

The status of neutron beam utilization in Korea

HANARO at Korea Atomic Energy Research Institute, which reached its first criticality on February, 1995, is a multi-purpose research reactor for application of reactor radiation to a variety of fields such as physics, materials science, biomedical research, irradiation technology, and neutron activation analysis.As for the neutron beam research, 6 horizontal beam ports out of total 7 ports of different types are available, and KAERI has pursued an extensive instrument development program since 1992 based on its long-term development plan for neutron scattering research and required instruments. A High Resolution Powder Diffractometer and a Neutron Radiography Facility are operational since late 1997 and 1996 respectively. A Four-Circle Diffractometer is under commission and a Small Angle Neutron Spectrometer will be operational in late 2000. SANS at cold neutron beam tube will be first operated using liquid nitrogen cooled Be filter and when the cold neutron source becomes available, it will be moved to the guide laboratory with proper modifications.Research work on the instruments in operation was started by the internal and the external users since their full kale normal operation. The number of users and their experiments are increasing continuously. T meet the rapidly increasing demand of external user nationwide, we had to use most of the available institute resources for the on-going development of instruments till last year.In addition to above instruments, a Polarized Neutron Spectrometer, a Triple Axis Spectrometer, and a Neutron Reflectometer for which there is a strong request by external users from universities and industries are under discussion. With the available instruments under operation and the one's under planning, HANARO will provide an excellent combination of neutron instruments to meet the national research demand and the international collaborations, and will be well prepared for the future cold neutrons based research.Starting with the informal users program since 1998, various efforts by internal and external researchers to constitute the Users Group and to find ways to support users has been discussed and it was possible to conduct 3 workshops and 2 winter schoolsannually since 1997. A peer group of 15 members from universities, institutes, and industries was formed in October 1999, and a small trial support program by the ministry of science and technology (MOST) was launched in December 1999.

INDONESIA NEUTRON SCATTERING FACILITIES IN SERPONG

Description of the research reactor is presentedbriefly.The neutron beam facilities include onediffractometer for residual stress measurement, onediffractometer for single crystal structuraldetermination and texture measurement, one highresolution powder diffractometer, one neutronradiography facility, one triple axis spectrometer, onesmall angle neutron scattering spectrometer and onehigh resolution small angle neutron scatteringspectrometer.Current status of each instrument and itsperformance in the last three years are presented as wellas the future development and research programs.

Superspace-Group Approach to the Phase Transition of Cu8GeSe6

The high- and low-temperature forms, i.e., phase I (stable above 328 K) and phase II (stable below 328 K), of Cu8GeSe6 have been investigated by the powder X-ray diffraction method. Cu8GeSe6 II is hexagonal with A=12.6438(2), C=11.7570(1) Å, Z=6, and P63cm, and its structure is considered to be a superstructure of the high-temperature form, Cu8GeSe6 I (hexagonal, a=7.3164(4)≅A/3, c=11.7679(7) Å, Z=2, and P63mc). Rietveld analysis of Cu8GeSe6 I (350 K) and II (290 K) has been performed using diffraction data measured by a high-resolution powder diffractometer and synchrotron X-ray radiation. For Cu8GeSe6 II, a four-dimensional superspace group for commensurate modulation, P63mc(1/3 1/3 0), with basic cell constants a=7.2999, c=11.7570 Å has been successfully applied (Rwp=0.054). The superspace-group description allows uniform treatment of both forms, and the phase transition of Cu8GeSe6 is explained in terms of the presence and absence of commensurate modulation waves.

Structural study of NiO2 and CoO2 as end members of the lithiated compounds by in situ high resolution X-ray powder diffraction

In-situ X-ray diffraction has been carried out on LixNiO2 and LixCoO2 batteries, using the high resolution powder diffractometer BM16 at ESRF (Grenoble, France). Diffraction was performed in transmission geometry through 1-mm thick Bellcore-type plastic batteries. The batteries were controlled in potentiostatic mode. During these experiments, end-members NiO2 and CoO2 have been isolated, and high resolution patterns have been recorded in order to solve their structures from powder data. NiO2 structure is of CdI2 type, with a monoclinic distortion. CoO2 seems to be of CdCl2 type also with a monoclinic distortion.

High-temperature phases of NaNbO3 and NaTaO3.

The high-temperature phases of the perovskites sodium niobate, NaNbO(3), and sodium tantalate, NaTaO(3), have been re-examined using the high-resolution powder diffractometer HRPD at the ISIS neutron spallation source; the two materials show the same sequence of phases with tilted octahedra. Diffraction patterns were measured every 5 K allowing structural changes with temperature within a single phase to be determined for the first time. Previous structure determinations within one phase had been performed at a single temperature only. The octahedra are tilted about pseudocubic <100> directions and are also deformed; the magnitude of the deformation is shown to be proportional to the square of the angle of tilt as expected from a phenomenological theory applied to such transitions. The structures of NaNbO(3) between 753 and 793 K and of NaTaO(3) below 758 K are not as reported in the literature.

New high- and low-temperature apparatus for synchrotron polycrystalline X-ray diffraction.

A high-temperature furnace with an induction heater coil and a cryogenic system based on closed-cycle refrigeration have been assembled to enhance the non-ambient powder diffraction facilities at the Synchrotron Radiation Source, Daresbury Laboratory. The commissioning of the high- and low-temperature devices on the high-resolution powder diffractometer of Station 2.3 is described. The combined temperature range provided by the furnace/cryostat is 10-1500 K. Results from Fe and NH(4)Br powder samples are presented to demonstrate the operation of the apparatus. The developments presented in this paper are applicable to a wide range of other experiments and diffraction geometries.

Structure investigation of defect MgO - high temperature process catalyst

Structure refinement of defect MgO containing acetate and carbonate groups has been performed. The experiment was carried out on high resolution powder diffractometer in Siberian Synchrotron Radiation Center, Novosibirsk. The results demonstrated possibility of admixtures to insert into the structure of MgO by two different ways. The reliability of both models has been estimated. These models provided the decrease of R-factor down to 2.0–2.2% in contrast to the ideal MgO structure R-factor (9.5%).

Time-of-flight neutron diffraction study on lithium dinitride iodide, Li 7N 2I

The structure of Li 7N 2I has been redetermined from neutron diffraction data using the high resolution powder diffractometer (HRPD) at the spallation source ISIS, UK. The title compound crystallizes in the space group F4¯3m (No.216), a=1038.797(1) pm with eight formula units per unit cell. The Li 7N 2I-structure comprises a cationic Li 13N 4 staggered+ framework which is built of monocapped octahedra. While all Li atoms at the vertices are shared between two neighbouring units, the capping metal atom is shared by four octahedra. The Li 13N 4 staggered+ network is closely related to the B 2X 6 octahedral framework observed in the pyrochlore structure. Large voids in the structure are occupied by iodide and a Li +T ion pair. There is evidence that the nonsphericity of the Li +I − dipole induces a complicated Lidisorder in the Li-N framework.

Supermirror neutron guide tube on Sirius, the high resolution powder diffractometer at KENS

A neutron guide tube was mounted on Sirius, the high-resolution powder diffractometer newly installed at Neutron Science Laboratory (KENS) at High Energy Accelerator Researh Organization (KEK), and its performance was investigated. A NiC/Ti supermirror with the critical wave number triple of that of natural nickel was employed for the guide tube coating in order to utilize shorter wavelengths (∼1 Å) required on the powder diffractometry. The wavelength-dependent intensity gain is observed, which enhances the performance of Sirius over the powder diffractometer already existing at KENS without a guide tube.