LaNiO2: Synthesis and structural characterization

The preparation of a single phase LaNiO₂ by controlled H₂ reduction of the perovskite LaNiO₃ is reported. The different steps of the synthesis are detailed. The structural characterization is made by X-ray diffraction (XRD) and neutron powder diffraction (NPD) and discussed; the derived crystal structure is the infinite-layer CaCuO₂. Both XRD and NPD patterns are characterized by anisotropic shape broadening originating from size effect linked to the reduction process. From NPD, the LaNiO₂ powder is composed of platelet-like crystallites having an average thickness equal to 20 nm along the [001] direction. A modulation of the neutron diffraction background is observed and discussed in connection to the reduction process.     

Neutron diffraction studies of Gd2Zr2O7 pyrochlore

The structure of Gd₂Zr₂O₇ pyrochlore over the temperature range 4-300 K has been refined from powder neutron diffraction data. The sample was enriched in ¹⁶⁰Gd to avoid the high neutron absorption of naturally occurring Gd. The diffraction pattern showed well resolved superlattice reflections indicative of the pyrochlore structure and no evidence is found for anion-disorder from the structural refinements.     

Magnetism and structural chemistry of the n=2 Ruddlesden-Popper phase La3LiMnO7

Polycrystalline samples of the n=2 Ruddlesden-Popper phase La₃LiMnO₇ have been prepared and characterized. X-ray and neutron diffraction suggest that the structure is tetragonal with a disordered distribution of Li and Mn cations over the octahedral sites, but ⁶Li MAS NMR shows that the Li and Mn are 1:1 ordered locally. Electron microscopy shows that the stacking of the cation-ordered, perovskite-like bilayers along the crystallographic z-axis is disordered on the distance scale sampled by X-ray and neutron diffraction. Magnetometry data and neutron diffraction data collected at 2 K together suggest that the Mn cations within each structural domain order antiferromagnetically at 14 K, but that the disorder along z prevents the establishment of long-range magnetic order.     

New determination method of the neutron diffraction system resolution at the Algerian Es-Salam research reactor

The aim of this article is to determine the resolution of the neutron diffraction system (NDS) installed around the Algerian Es Salam research reactor. By using a new method based on neutron radiography technique we have measured the beam divergence at the exit of Soller Collimator (α₂) and hence determine effective collimations. The determination of the adequate resolution of our NDS is performed on experimental results obtained from neutron diffraction patterns for different collimation divergences (α₂) and (α₃) values obtained from several apertures sizes (S ₂) and (S ₃).     

Structural and Magnetic Chemistry of La2Sr2BMnO8 (B=Mg, Zn)

Polycrystalline samples of the layered perovskites La₂Sr₂MgMnO₈ and La₂Sr₂ZnMnO₈ have been studied by X-ray and neutron powder diffraction, electron diffraction and magnetometry. X-ray and neutron powder diffraction indicate that the average structure is that of K₂NiF₄, with disordering of Mn and (Zn, Mg) cations over the octahedral sites. Electron diffraction data indicate that cation ordering is present over these sites in the xy planes, with the xy ordered planes being stacked in a disordered manner along z. No long-range magnetic ordering is observed in the temperature range 5≤T (K)≤300.     

Neutron powder diffraction and first-principles computational studies of CuLixMg2−x (x≅0.08), CuMg2, and Cu2Mg

A small addition of Li changes the orthorhombic structure of CuMg₂ to hexagonal CuLi_xMg_2−x (x=0.08). Determining the Li content of the ternary phase and Li atomic positions was our main objective for this work. For this reason we performed neutron diffraction at several different temperatures below and above room temperature. The results obtained on two neutron powder diffractometers were compared with X-ray diffraction (XRD) data, and with first-principles calculations. The first-principles calculations are in good agreement with Rietveld-refined data from neutron diffraction, but do not show a marked preference for one of several possible Li sites. The pair distribution function (PDF) fitting is consistent with Li substituting only Mg1 (1/2, 0, z). Interstitial spaces in the structure of CuMg₂ and of CuLi_xMg_2−x were also considered, but are unlikely to be occupied by Li. Neutron diffraction data for binary CuMg₂ and Cu₂Mg were also obtained.     

Neutron diffraction study of La4LiAuO8: Understanding Au in an oxide environment

Owing to gold's oxophobicity, its oxide chemistry is rather limited, and elevated oxygen pressures are usually required to prepare ternary and quaternary oxide compounds with gold ions. The Au³⁺ oxide, La₄LiAuO₈, is remarkable both because it can be prepared at ambient pressure in air, and because of its unusual stability toward thermal decomposition and reduction. The structure of La₄LiAuO₈ was established by Pietzuch et al. using single crystal X-ray diffraction [1]. The compound adopts an ordered modification of the Nd₂CuO₄ structure, containing two-dimensional sheets in which AuO₄ square planes are separated from one another by LiO₄ square planes. In light of the meager X-ray scattering factors of Li and O, relative to La and Au, we report here a neutron powder diffraction study of La₄LiAuO₈, definitively confirming the structure. To our knowledge, this is the first reported neutron diffraction study of any stoichiometric oxide compound of gold. X-N maps, which make use of nuclear positions obtained from Rietveld refinement of time-of-flight neutron diffraction data and electron densities obtained from synchrotron X-ray powder diffraction data, point to the highly covalent nature of the Au-O bonding in La₄LiAuO₈. This is in good agreement with charge densities and Bader charges obtained from full density functional relaxation of the structure.     

Crystallographic and magnetic structure of Tb3Ge5

The compound Tb₃Ge₅ has an orthorhombic structure related to the tetragonal α-ThSi₂ structure. Results of a detailed structure determination based on neutron diffraction are reported. Magnetic measurements and neutron diffraction showed Tb₃Ge₅ to order antiferromagnetically below T_N = 17 K. There is a close relationship between the magnetic structure and the orthorhombic deformation if the crystallographic structure of Tb₃Ge₅ is viewed as a derivative of the (defect) α-ThSi₂ structure.     

ChemInform Abstract: Study on the Crystal Structure of the Rare Earth Oxyborate Yb26B12O57 from Powder X‐Ray and Neutron Diffraction.

The title compound, previously assigned as Yb₃BO₆ is characterized by powder X‐ray and neutron diffraction, ¹¹B NMR spectroscopy, electron diffraction, high angle angular dark field‐STEM, and magnetic measurements.     

Polarized neutron diffraction and its application to spin density studies

Spin density distributions in molecular compounds containing unpaired electrons have been studied by polarized neutron diffraction (PND). The spin density distributions provide a unique perspective of the magnetic properties of the compounds. The background and fundamentals of polarized neutron diffraction are summarized in this review, followed by examples of applications in inorganic and organic chemistry. Spin densities in several compounds that are obtained by polarized neutron diffraction are highlighted. Spin densities in single molecular magnet [Fe₈O₂(OH)₁₂(tacn)₆]⁸⁺ and cyano-bridged K₂[Mn(H₂O)₂]₃[Mo(CN)₇]₂·6H₂O demonstrate how to obtain magnetic interaction in the complexes by PND. PND studies of Ru(acac)₃, containing one single unpaired electron, show small spin densities in this complex. Finally the use of PND in studying nitronyl nitroxide radicals is given. Our goal in this review is to illustrate how PND functions and how it serves as a sensitive tool in directly probing spin density in molecules.     

The structure and magnetic properties of chromium(III) molybdate

Magnetic susceptibility measurements have shown that Cr₂(MoO₄)₃ orders magnetically at 42 K. Powder neutron diffraction experiments at 295 and 5 K indicate that Cr₂(MoO₄)₃ is chemically and magnetically isostructural with the L-type ferrimagnet Fe₂(MoO₄)₃, and has a magnetic moment of 2.5 ± 0.2 μ_B per cation at 5 K. The limitations imposed on powder neutron diffraction methods by particle-size effects are discussed.     

ChemInform Abstract: The Crystal Structures of the Low-Temperature Modifications of Deuterium Iodide - a Neutron Study.

Solid DI, obtained by reacting D₂O, red P, and I2, is investigated by neutron powder diffraction.     

Synthesis and Structural Determination of the Disordered Bixbyite Cu3‐xSb1+xO5.5+3x/2 with Spin‐Glass Behaviour

The ternary copper antimony oxide Cu_3‐xSb_1+xO_5.5+3x/2 (x=0.23) has been synthesized under 0.8–1.3 MPa pO₂ at 1022–1082 °C. Rietveld refinements of X‐ray and neutron powder diffraction patterns concluded that the oxide adopts a bixbyite type structure, crystallising in the cubic space group Ia‐3 with the unit cell parameter a=9.61164(4) Å at room temperature from powder neutron diffraction data. The cationic 8b and 24d sites were found to be occupationally disordered where both Cu and Sb could be found on both sites. This is supported by X‐ray absorption spectroscopy experiments showing more than one possible Cu environment. There was a significant net deficiency of oxygen in the compound which was first inferred from observations of a thermochromic‐like phenomena and also seen from in situ high temperature neutron diffraction experiments. Magnetic susceptibility and magnetization measurements show paramagnetic behaviour with spin‐glass like transition below 6 K.     

Structure of Nano‐sized CeO2 Materials: Combined Scattering and Spectroscopic Investigations

The structure of several nano‐sized ceria, CeO₂, systems was investigated using neutron and X‐ray diffraction and X‐ray absorption spectroscopy. Whilst both diffraction and total pair distribution functions (PDFs) revealed that in all of the samples the occupancy of both Ce⁴⁺ and O^2? are very close to the ideal stoichiometry, the analysis using Reverse Monte Carlo technique revealed significant disorder around oxygen atoms in the nano‐sized ceria samples in comparison to the highly crystalline NIST standard. In addition, the analysis revealed that the main differences observed in the pair correlations from various X‐ray and neutron diffraction techniques were attributable to the particle size of the CeO₂ prepared by the reported three methods. Furthermore, detailed analysis of the Ce L₃‐ and K‐edge EXAFS data support this finding; in particular the decrease in higher shell coordination numbers with respect to the NIST standard, is attributed to differences in particle size.     

Structural and Magnetic Properties of Pr2BaCuO5 Oxide

The Pr₂BaCuO₅ oxide has been prepared by using a precursor method. X‐ray and neutron diffraction data reveal that this mixed oxide crystallizes with the so‐called Nd₂BaPtO₅‐type structure, showing tetragonal symmetry and space group P4/mbm. Magnetic susceptibility, magnetization and specific heat measurements reveal that Pr₂BaCuO₅ oxide behaves as antiferromagnet, where the Pr³⁺ and Cu²⁺ sublattices become simultaneously ordered at 15 K. Preliminary neutron diffraction studies confirm this proposed antiferromagnetic ordering and it can be described by the wave vector k = [0,0,0].     

Neutron crystal structure analysis of polyethylene‐d4: The application of a neutron imaging plate

Neutron diffraction provides a more detailed structure than X‐ray diffraction. In this study, a neutron crystal structure analysis of polyethylene‐d₄ was carried out with a neutron imaging plate. This was the first crystal analysis of the crystalline polymer with the neutron fiber pattern. The procedure was almost the same as that in a previous work, in which the neutron structure analysis was carried out on the basis of the equatorial reflections. The azimuthal angle of the molecule with respect to the a axis was estimated to be 46.3°. This corresponded well to the value of 45° estimated in the previous work within the accuracy of the standard deviations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3836–3839, 2004     

Investigations of the magnetic properties of the Yb6Mn23 intermetallic compound

The magnetic properties of the Yb₆Mn₂₃ intermetallic compound were investigated using magnetometry and neutron diffraction. The Yb₆Mn₂₃ phase was found to have a ferrimagnetic structure. The magnetic and chemical unit cells of the compound coincide and the Curie point is 406 K. Neutron diffraction and magnetic measurements at low temperatures indicate that the ytterbium sublattice magnetization rapidly compensates the manganese sublattice magnetization.     

Zirconium dodecarborides ZrB12. Confirmation of the B12 cubooctahedral unit

Using powder neutron diffraction and Rietveld's method of profile refinement, the structure of ZrB₁₂ was confirmed.     

Hydrothermal growth of ceria nanoparticles

Peculiarities of CeO₂ nanoparticle coarsening during hydrothermal treatment in a neutral medium are determined by small-angle neutron scattering, powder X-ray diffraction, low-temperature nitrogen adsorption, and transmission electron microscopy. Coherent intergrowth of individual CeO₂ crystallites is the main scenario of nanoparticle coarsening.