Four-circle Diffractometer Research Articles

Space-Group Determination of Superlattice Structure Due to Electric Toroidal Ordering in Ca5Ir3O12

Synchrotron X-ray diffraction measurements on a single crystal of Ca5Ir3O12 were performed to clarify the details of the superlattice reflections characterized by \(\mathbf{q} = (1/3,1/3,1/3)\). A search for superlattice reflections in a wide reciprocal space was performed using an imaging plate, and it was confirmed that there were no superlattice reflections at other than \(\mathbf{q} = (1/3,1/3,1/3)\). From the extinction rule of the superlattice reflections, the space group of the crystal structure below 105 K was found to be R3. The details of the superlattice reflections at specific q were investigated using a four-circle diffractometer. The temperature dependence of the integrated intensity at several q confirms that the order parameter of the phase transition of Ca5Ir3O12 at 105 K belongs to an A2 irreducible representation in the point group C3v from the discussion based on the Landau theory of phase transitions. The basis function of the A2 irreducible representation, which is a rotation around the c-axis, corresponds to an electric toroidal dipole.

CRYSTAL STRUCTURE OF THE TmNi5

Сrystal structure of the TmNi5 compound has been investigated by means of X-ray single crystal method (Oxford Diffraction X’calibur four-circle diffractometer, MoKα radiation) for the first time: CaCu5-type structure, Pearson symbol hP6, space group P6/mmm, a = 4.8684(12), c = 3.9541(7) Å, R1 = 0.0529, wR2 = 0.1835 for 80 reflections. Similarly to intermetallic compounds with high transition metal content, atoms in the title structure have rather high coordination numbers: 20 for thulium and 12 for nickel.

CRISTAL-ITE: a single-crystal X-ray diffractometer scale model for scientific dissemination

This article presents the design and manufacture of an automated scale model of a four-circle single-crystal X-ray diffractometer that can be used for scientific dissemination. The purpose of this device is to reach out to the wider public and students to introduce them in an entertaining way to one of the laboratory apparatuses to which they do not usually have access, to talk to them about crystallography in the broadest sense, to develop concepts in various fields of science and technology, and to initiate interest and discussions. The main technical aspects of the project are described, with the expectation that such an approach could be useful to anyone involved in scientific dissemination and could be developed for other laboratory equipment and other disciplines. This kind of device can also be the subject of scientific and technological projects in close collaboration with educational institutions.

Синтез и строение продукта реакции пента-пара-толилсурьмы с гептафторпропил(t-бутил)дикетоном-1,3 p-Tol4Sb[t-BuC(O)СHС(О)С3F7

Penta(para-tolyl)antimony reacts with heptafluoropropyl(t-butyl)diketone-1,3 with the splitting out of toluene and formation of the substitution product p-Tol4Sb[t-BuC(O)СHС(О)С3F7] (1), yielding 82%. The compound was identified by IR spectroscopy and X-ray diffraction analysis. The X-ray analysis was performed on an automatic four-circle diffractometer D8 Quest Bruker (MoK radiation, λ = 0.71073 Å, graphite monochromator) at 293 K. Crystal size is 0.59 × 0.48 × 0.13 mm, P-1, a = 10.47(2), b = 10.94(2), c = 17.04 (3) Å, α = 73.12 (6), β = 88.94(8), γ = 89.94(8) deg., V = 1867 (7) Å3, Z = 2, ρ = 1.39 g/cm3, F(000) = 792.0, the 2θ interval is 3.89–56.999 deg., R1 = 0.2213, wR2 = 0.5429. According to the X-ray diffraction data, compound 1 is a molecular complex, in which the antimony atoms have an octahedral coordination with two oxygen atoms and two carbon atoms in the equatorial plane; the axial positions are occupied by the two remaining tolyl ligands. The CSbC axial angle is strongly distorted and is equal to 159.6 (8)°. The CSbO diagonal angles in the equatorial plane are 167.1(7)°, 166.9(7)°. The lengths of the Sb–C bonds are 2.11(2) and 2.19 (3) Å. The formation of the chain spatial structure of crystals is due to formation of bonds between the molecules involving fluorine (H∙∙∙F 2.64−2.83 Å) and carbon (C∙∙∙F 3.005 Å) atoms. Complete tables of atomic coordinates, bond lengths, and valence angles are deposited in the Cambridge Structural Data Bank (No. 2067768 (1); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/data_request/cif).

Polytypism of Cronstedtite from Ouedi Beht, El Hammam, Morocco

AbstractThe present study deals with accurate identification of polytypes, twins, and allotwins – oriented crystal associations of more than one polytype. The trioctahedral 1:1 layered silicate cronstedtite was studied using single-crystal X-ray diffraction data collected with a four-circle diffractometer equipped with a CCD detector. The sample from the skarn occurrence, Ouedi Beht, El Hammam, Morocco, was explored. It contains cronstedtite in fibrous massive aggregates in the central part, and euhedral crystals in surrounding veinlets and druses. The reciprocal space (RS) sections created by the diffractometer software and presented here were used to determine the OD (ordered-disordered) subfamilies (Bailey’s group A, B, C, D) and to identify polytypes. The chemical compositions of some crystals were determined thereafter by electron probe microanalysis (EPMA-WDS). Some crystals studied are more or less complicated allotwins. Polytypes were thus separated by cleaving crystals into smaller parts in many cases. All polytypes found belong to subfamilies A or D. The following polytypes of the subfamily A were identified: 2M1 (a = 5.49, b = 9.51, c = 14.40 Å, β = 97.30°, space group Cc), 1M (a = 5.51, b = 9.54, c = 7.33 Å, β = 104.5°, Cm), 3T (a = 5.51, c = 21.32 Å, P31), 6T2 (a = 5.50, c = 42.60 Å, P31). 2M1 and 3T were present as isolated crystals or separated by cleaving, otherwise all these polytypes are parts of allotwins. The 2M1 polytype is sometimes twinned by reticular pseudo merohedry with twin index n = 3 and 120° rotation about the chex axis as the twin operation. Allotwins of 1M + twinned 2M1 polytypes are also present. Another kind of twinning, with rotation by (2n+1)×60° about chex is rare. The subfamily D is represented mostly by 2H1 and 2H2 polytypes, a = 5.50, c = 14.25 Å, space groups P63cm (2H1), P63 (2H2). In addition, several six-layer (a = 5.49, c = 42.80 Å), mostly non-MDO polytypes were separated from allotwins by cleaving. In order to identify them, 24 possible stacking sequences were modeled, diffraction patterns calculated, graphical identification diagrams constructed, and comparisons made with actual RS sections. This simulation revealed that five pairs of sequences provided identical diffraction patterns. Polytypes actually found correspond to the following sequences: 1 (6T1), 5 (proposed Ramsdell’s symbol 6T3), 8+10 (6T5), 11+12 (6T4), 24 (6T6, trigonal polytypes, space group type P3), 22 (6R1), and 23 (6R2, rhombohedral polytypes, space group type R3c and R3, respectively). The RS section corresponding to the hexagonal polytype 6H2 (sequence 14) was also found. However, diffraction patterns geometrically indistinguishable can be produced by the twin with rotation by 180° about chex as a twin operation of the rhombohedral polytype 6R2 (sequence 23). Several aggregates with fiber texture of polytype 2H2 were separated from the central part. Use of EPMA-WDS revealed Fe and Si along with significant amounts of Mn and Mg. Crystals from veins were more Mn- and Mg-rich than these from the central part. Traces of Cl, S, and Al are present also.

Structural and electrochemical properties of the binary silicides Eu5Si3 and EuSi

Abstract The crystal structures of Eu5Si3 and EuSi were studied in detail by X-ray single-crystal diffraction. The single crystals were selected from arc-melted and annealed samples. X-ray diffraction was performed at room temperature on an Oxford Diffraction X’calibur Atlas four-circle diffractometer (MoKα radiation). Eu5Si3 adopts the tetragonal Cr5B3-type: space group I4/mcm (# 140), Pearson code tI32, Z = 4, a = 7.9339(6), c = 15.308(2) Å. The compounds with equiatomic composition EuSi crystallize in the structure type TlI: space group Cmcm (# 63), Pearson code oS8, Z = 4, a = 4.6955(6), b = 11.1528(13), c = 3.9845(4) Å. The silicides Eu5Si3 and Li2Si form during electrochemical lithiation (charge process) of EuSi. The electrochemical process 5EuSi + 4Li+ + 4e − ↔ Eu5Si3 + 2Li2Si is reversible, and the discharge specific capacity at 1C rate reached 140 mAhg−1 and the Coulombic efficiency is 93%.

X-ray molecular orbital analysis. II. Application to diformohydrazide, (NHCHO)2.

The molecular orbitals (MOs) of diformohydrazide have been determined from the electron density measured by X-ray diffraction. The experimental and refinement procedures are explained in detail and the validity of the obtained MOs is assessed from the crystallographic point of view. The X-ray structure factors were measured at 100 K by a four-circle diffractometer avoiding multiple diffraction, the effect of which on the structure factors is comparable to two-centre structure factors. There remained no significant peaks on the residual density map and the R factors reduced significantly. Among the 788 MO coefficients, 731 converged, of which 694 were statistically significant. The C-H and N-H bond distances are 1.032 (2) and 1.033 (3) Å, respectively. The electron densities of theoretical and experimental MOs and the differences between them are illustrated. The overall features of the electron density obtained by X-ray molecular orbital (XMO) analysis are in good agreement with the canonical orbitals calculated by the restricted Hartree Fock (RHF) method. The bonding-electron distribution around the middle of each bond is well represented and the relative phase relationships of the π orbitals are reflected clearly in the electron densities on the plane perpendicular to the molecular plane. However, differences are noticeable around the O atom on the molecular plane. The orbital energies obtained by XMO analysis are about 0.3 a.u. higher than the corresponding canonical orbitals, except for MO10 to MO14 which are about 0.7 a.u. higher. These exceptions are attributed to the N-H...O'' intermolecular hydrogen bond, which is neglected in the MO models of the present study. The hydrogen bond is supported by significant electron densities at the saddle points between the H(N) and O'' atoms in MO7, 8, 14 and 17, and by that of O''-p extended over H(N) in MO21 and 22, while no peaks were found in MO10, 11, 13 and 15. The electron density of each MO clearly exhibits its role in the molecule. Consequently, the MOs obtained by XMO analysis give a fundamental quantum mechanical insight into the real properties of molecules.

Multipurpose diffractometer for in situ X-ray crystallography of functional materials

Laboratory X-ray diffractometers play a crucial role in X-ray crystallography and materials science. Such instruments still vastly outnumber synchrotron facilities and are responsible for most of the X-ray characterization of materials around the world. The efforts to enhance the design and performance of in-house X-ray diffraction instruments benefit a broad research community. Here, the realization of a custom-built multipurpose four-circle diffractometer in the laboratory for X-ray crystallography of functional materials at Tel Aviv University, Israel, is reported. The instrument is equipped with a microfocus Cu-based X-ray source, collimating X-ray optics, four-bounce monochromator, four-circle goniometer, large (PILATUS3 R 1M) pixel area detector, analyser crystal and scintillating counter. It is suitable for a broad range of tasks in X-ray crystallography/structure analysis and materials science. All the relevant X-ray beam parameters (total flux, flux density, beam divergence, monochromaticity) are reported and several applications such as determination of the crystal orientation matrix and high-resolution reciprocal-space mapping are demonstrated. The diffractometer is suitable for measuring X-ray diffraction in situ under an external electric field, as demonstrated by the measurement of electric-field-dependent rocking curves of a quartz single crystal. The diffractometer can be used as an independent research instrument, but also as a training platform and for preparation for synchrotron experiments.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP at BESSY II.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP for optical pump/X-ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four-circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non-linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time-resolution of 17 ps is achieved with the `low-α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X-ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time-resolved detection of the diffracted hard X-ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields arepresented.

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.

Alluaudite-Group Phosphate and Arsenate Minerals

ABSTRACT A systematic study of alluaudite, hagendorfite, and varulite was done using single-crystal X-ray diffraction, powder diffraction, and electron probe microanalysis of samples from 12 separate localities. The crystal structures of the representative alluaudite and hagendorfite samples were refined to R1 indices of 3.7 and 1.8%, respectively, using a Siemens P4 automated four-circle diffractometer equipped with a graphite monochromator and MoKα X-radiation. These samples and several others were analyzed with an electron microprobe to study variations in chemical composition. For the single-crystal analyses, the resulting unit formulae are (Na0.11□0.89)(Na0.59Mn0.27Ca0.14)Mn1.00(Fe3+1.64Al0.24Mg0.13)(PO4)3 for alluaudite, (Na0.79□0.21)(Na0.81Mn2+0.19)(Mn0.70Fe2+0.30)(Fe2+1.72Mg0.27Al0.01)(PO4)3 for hagendorfite, and (Na0.84□0.16)(Na0.71Ca0.23□0.06)Mn1.00(Fe3+0.89Fe2+0.68Mn0.42Mg0.01)(PO4)3 for varulite. Originally, a nomenclature scheme was proposed for the alluaudite-group minerals that was based on sequentially distributing the cations in the cell according to increasing polyhedron size, matching that size with increasing ionic radii of the cations. For alluaudite, the structural formula was written as X(2)4X(1)4M(1)4M(2)8(PO4)12, with the sites ordered in decreasing size of the discrete polyhedra. Later, the formula [A(2)A(2)'A(2)”2][A(1)A(1)'A(1)”2]M(1)M(2)2(PO4)3 was proposed, which takes into account the distinct crystallographic sites in the channels of the structure. More recently there has been a revision to the nomenclature of the group. The simplified structural formula for the alluaudite-type is now A(2)'A(1)M(1)M(2)2(TO4)3; the new nomenclature scheme has been adopted by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC), based on the contents of the M(1) and M(2) octahedral sites, and the results are reviewed here. Compounds belonging to the alluaudite structural family have been the focus of synthetic mineral studies for decades owing to the open-framework architecture and their unique physical properties. Improvements in synthesis methods have allowed researchers to substitute a wide range of elements into the alluaudite structure.

Строение органических и элементоорганических соединений. Сообщение 2

The structures of five organoantimony compounds Ph4SbOCH2Ph (1), p-Tol4SbBr (2), [Ph4Sb][I3] (3), [Ph3PCH2СHMe2][I3] (4) and [Ph3P(CH2)3PPh3]+2 [I]2  I2 (5) were determined by X-ray diffraction analysis. X-ray diffraction of the compounds was carried out on an automatic four-circle diffractometer D8 Quest Bruker (МоКα, λ = 0,71073 Å, 293 К. (1), crystal size 0.3 × 0.18 × 0.1 mm, P21/c, a = 14.512(7), b = 10.554(4), c = 17.209(9) Å, β = 106.91(2) deg., V = 2522(2) Å3, Z = 4, R1 = 0.0206, wR2 = 0.0457. (2), crystal size 0.38 × 0.22 × 0.18 mm, P21/n, a = 9.896(6), b = 23.349(11), c = 12.149(6) Å, β = 113.393(18) deg., V = 2576(2) Å3, Z = 4, R1 = 0.0321, wR2 = 0.0673. (3), crystal size 0.3×0.21×0.13 mm, P2/n, a = 10.679(18), b = 8.178(14), c = 15.07(3) Å, β = 92.89(11) deg., V = 1315(4) Å3, Z = 2, R1 = 0.0297, wR2 = 0.0589. (4), crystal size 0.27×0.14×0.05 mm, P21/c, a = 10.199(5), b = 17.886(11), c = 13.300(9) Å, β = 91.77(2), deg., V = 2425(2) Å3, Z = 4, R1 = 0.0531, wR2 = 0.1331. (5), crystal size 0.46×0.29×0.18 мм, P21, a = 8.613(3), b = 15.509(6), c = 14.875(5) Å, β = 93.349(11), deg., V = 1940(6) Å3, Z = 2, R1 = 0.0297, wR2 = 0.0678.

Polytypism of Cronstedtite From Nagybörzsöny, Hungary

AbstractThe present study provides an example of the accurate identification of polytypes of trioctahedral 1:1 layered silicates from single-crystal X-ray diffraction data collected with the aid of a four-circle diffractometer equipped with an area detector. Single crystals of the mineral cronstedtite from the Nagybörzsöny gold ore deposit, northern Hungary, were studied. The chemical composition of some crystals was determined by electron probe microanalysis (EPMA). The precession-like images of the reciprocal space (RS) sections created by the diffractometer software and presented in the study were used to determine the OD (ordered-disordered) subfamilies (Bailey’s groups A, B, C, D) and particular polytypes. With one exception, all crystals studied belong to subfamily A. The rare polytype 1M, a = 5.51, b = 9.54, c = 7.33 Å, β = 104.5°, space group Cm is relatively abundant in this occurrence. Another polytype 3T, a = 5.51, c = 21.32 Å, space group P31 was also found. Both polytypes occur separately or in mixed, mostly 1M dominant crystals. Some 1M polytype crystals are twinned by order 3 reticular merohedry with a 120° rotation along the chex axis as the twin operation. A rare 1M+3T mixed crystal with 1M part twinned also contains a small amount of subfamily C. A possible presence of the most common 1T polytype of this subfamily cannot be confirmed because of overlap of the characteristic reflections with those of 3T. Several completely disordered crystals produced diffuse streaks instead of discrete characteristic reflections on the RS sections. The EPMA revealed Fe, Si, traces of Mg, Al, S, and Cl. One black crystal originally considered to be cronstedtite was identified as (111) twinned sphalerite. Some crystals of cronstedtite are covered partially by a honey-brown crust or small crystals of siderite.

Impurity Composition and Lattice Parameters of High-Purity α-Mn

We have studied a high-purity manganese sample provided by the Exhibition–Collection of Extrapure Substances, operating on the basis of the Devyatykh Institute of Chemistry of High-Purity Substances, Russian Academy of Sciences, and analyzed for the concentration and trace levels of 59 elemental impurities. The content of the major component in it was 99.9993 wt %. Its growth surface was formed by intergrown and individual single crystals, from which samples for lattice parameter measurements were cut. Precision measurements were performed at room temperature (298 ± 1 K) over the entire Ewald sphere on an XCalibur four-circle diffractometer (Rigaku-Oxford Diffraction). The lattice parameters of single-crystal samples selected for measurements were determined using high-angle reflections. The unit-cell dimension of our samples turned out to exceed those reported previously by different groups for poly- and monocrystalline manganese samples.

SYNTHESIS AND STRUCTURE OF ORGANYLTRIPHENYLPHOSPHONIUM DICYANOARGENTATES: [Ph3P(CH2)3PPh3]2+ [Ag(CN)2]– [Br]– AND [Ph3PR]+ [Ag(CN)2]–, R = CH2CH2OH, CH2C6H4F-4

The reaction of potassium dicyanoargentate with organyltriphenylphosphonium bromides in an aqueous solution has led to synthesis of complexes [Ph3P(CH2)3PPh3]2+[Ag(CN)2]–[Br]– (1), [Ph3PR]+[Ag(CN)2]–, R = CH2CH2OH (2), CH2C6H4F-4 (3), whose structures have been characterized by X-ray diffraction analysis (XRD). It is known that the absorption range of cyano groups in IR spectra of organic and inorganic compounds is in the form of a narrow interval of 2200-2000 cm-1, which points at the absence of strong surroundings influence on vibrations of these bonds. The absorption bands in the range 1450-1435 cm-1 peculiar to the P-Ph bands that are present in the spectra of compounds 1, 2, 3 are apparent in the range 1437-1439 cm-1. The XRD data have been obtained at 293 K on a Bruker D8 QUEST automatic four-circle diffractometer: crystals 1 (C41H36AgBrN2P2, М 806.44, triclinic syngony, crystal size 0.72 × 0.37 × 0.3 mm), 2 (C22H20AgN2OP, M 467.24, triclinic syngony, crystal size 0.8 × 0.52 × 0.35 mm), 3 (C27H21AgFN2P, M 531.30, monoclinic syngony, crystal size 0.28 × 0.23 × 0.22 mm). According to the XRD data, crystals 1, 2, 3 contain organyltriphenylphosphonium cations and linear dicyanoargentate anions. Besides, bromide anions are observed in crystal 1. A characteristic feature of complexes with the [Ag(CN)2]− anions is their perspective utility for development of new nano- and liquid crystal systems. The organyltriphenylphosphonium cations have a distorted tetrahedral configuration: the CPC angles vary within the range 106.70(8)° - 113.37(9)°. In the [Ag(CN)2]−anions the CAgC angles equal 171.75(10)° – 178.37(8)°.

Finding a New B1-Type Phase in Single Crystals of Fe–Al and Fe–Ga Soft Magnetic Alloys

The atomic structure of Fe–Al (7 and 9 at % Al) and Fe–Ga (18 at % Ga) alloys is studied by X‑ray diffraction using a laboratory four-circle diffractometer. After refining annealing, single-crystal alloy samples were annealed in the ferromagnetic state (T TC), was quenched in room temperature water. Earlier, the authors reported on the peculiarities of the ordering of alloying atoms in B2 and D03 phase structures in quenched and annealed samples of these alloys. Here, we present and discuss the results of our observations in these alloys of a new phase with a face-centered cubic (fcc) lattice (B1-type structure with NaCl prototype and unit cell parameter ~5.2 nm). The fcc phase appears in the Fe–Al alloy as the aluminum concentration increases from 7 to 9 at %; it is observed in the Fe–18 at % Ga alloy, and its volume fraction increases after annealing in the ferromagnetic state in comparison with a quenched alloy sample. In these alloys (9 at % Al) and (18 at % Ga), different ways of embedding fcc crystals in the bcc phase of single crystals are realized; i.e., the axes of the fcc lattice are directed in four different ways relative to the axes of the bcc lattice.

Влияние отжига в ферромагнитном состоянии на структуру сплава железа с 18 at.% галлия

AbstractThe atomic structure of the iron–gallium alloy containing 18 at % Ga has been studied by X-ray diffraction. The samples were annealed in the paramagnetic ( T > T _C) and ferromagnetic ( T < T _C) state. In the first case, the structural state was fixed by quenching from the annealing temperature into water; in the second case, the structural state was obtained by slow cooling. The structural studies of the single-crystal samples were conducted on a four-circle X-ray diffractometer at room temperature. From the X-ray diffraction data, it follows that the alloy, independently on the heat treatment, contains B 2 clusters, i.e., locally ordered regions with the CsCl-type structure observed in alloys of iron with silicon (to 10 at % Si) and aluminum (7 at % Al) before. In addition to the B 2‑clusters, regions with the D 0_3 short-range order are observed in the quenched sample; the sizes of these regions significantly increases after annealing in the ferromagnetic state, i.e., a long-range order forms. The relation of the fine structural changes in the alloy due to various heat treatments with its magnetoelastic and magnetostriction properties is discussed.

Обнаружение новой фазы типа B1 в монокристаллах магнитомягких сплавов Fe-Al и Fe-Ga

AbstractThe atomic structure of Fe–Al (7 and 9 at % Al) and Fe–Ga (18 at % Ga) alloys is studied by X‑ray diffraction using a laboratory four-circle diffractometer. After refining annealing, single-crystal alloy samples were annealed in the ferromagnetic state ( T < T _C). One sample of the Fe–18 at % Ga alloy, after short holding in the paramagnetic state ( T > T _C), was quenched in room temperature water. Earlier, the authors reported on the peculiarities of the ordering of alloying atoms in B 2 and D 0_3 phase structures in quenched and annealed samples of these alloys. Here, we present and discuss the results of our observations in these alloys of a new phase with a face-centered cubic (fcc) lattice ( B 1-type structure with NaCl prototype and unit cell parameter ~5.2 nm). The fcc phase appears in the Fe–Al alloy as the aluminum concentration increases from 7 to 9 at %; it is observed in the Fe–18 at % Ga alloy, and its volume fraction increases after annealing in the ferromagnetic state in comparison with a quenched alloy sample. In these alloys (9 at % Al) and (18 at % Ga), different ways of embedding fcc crystals in the bcc phase of single crystals are realized; i.e., the axes of the fcc lattice are directed in four different ways relative to the axes of the bcc lattice.

DEMAND, a Dimensional Extreme Magnetic Neutron Diffractometer at the High Flux Isotope Reactor

A two-dimensional (2D) Anger camera detector has been used at the HB-3A four-circle single-crystal neutron diffractometer at the High Flux Isotope Reactor (HFIR) since 2013. The 2D detector has enabled the capabilities of measuring sub-mm crystals and spin density maps, enhanced the efficiency of data collection and phase transition detection, and improved the signal-to-noise ratio. Recently, the HB-3A four-circle diffractometer has been undergoing a detector upgrade towards a much larger area, magnetic-field-insensitive, Anger camera detector. The instrument will become capable of doing single-crystal neutron diffraction under ultra-low temperatures (50 mK), magnetic fields (up to 8 T), electric fields (up to 11 kV/mm), and hydrostatic high pressures (up to 45 GPa). Furthermore, half-polarized neutron diffraction is also available to measure weak ferromagnetism and local site magnetic susceptibilities. With the new high-resolution 2D detector, the four-circle diffractometer has become more powerful for studying magnetic materials under extreme sample environment conditions; hence, it has been given a new name: DEMAND.

Effect of Annealing in a Ferromagnetic State on the Structure of an Fe–18 at % Ga Alloy

The atomic structure of the iron–gallium alloy containing 18 at % Ga has been studied by X-ray diffraction. The samples were annealed in the paramagnetic (T > TC) and ferromagnetic (T < TC) state. In the first case, the structural state was fixed by quenching from the annealing temperature into water; in the second case, the structural state was obtained by slow cooling. The structural studies of the single-crystal samples were conducted on a four-circle X-ray diffractometer at room temperature. From the X-ray diffraction data, it follows that the alloy, independently on the heat treatment, contains B2 clusters, i.e., locally ordered regions with the CsCl-type structure observed in alloys of iron with silicon (to 10 at % Si) and aluminum (7 at % Al) before. In addition to the B2‑clusters, regions with the D03 short-range order are observed in the quenched sample; the sizes of these regions significantly increases after annealing in the ferromagnetic state, i.e., a long-range order forms. The relation of the fine structural changes in the alloy due to various heat treatments with its magnetoelastic and magnetostriction properties is discussed.