The crystallographic and magnetic structure of Ni(IO 3) 2.2D 2O

We have investigated the crystal structure of Ca(BD4)2 by combined synchrotron radiation X-ray powder diffraction, neutron powder diffraction, and ab initio calculations. Ca(BD4)2 shows a variety of structures depending on the synthesis and temperature of the samples. An unknown tetragonal crystal of Ca(BD4)2, the beta phase has been solved from diffraction data measured at 480 K on a sample synthesized by solid-gas mechanochemical reaction by using MgB2 as starting material. Above 400 K, this sample has the particularity to be almost completely into the beta phase of Ca(BD4)2. Seven tetragonal structure candidates gave similar fit of the experimental data. However, combined experimental and ab initio calculations have shown that the best description of the structure is with the space group P4(2)/m based on appropriate size/geometry of the (BD4)tetrahedra, the lowest calculated formation energy, and real positive vibrational energy, indicating a stable structure. At room temperature, this sample consists mainly of the previously reported alpha phase with space group Fddd. In the diffraction data, we have identified weak peaks of a hitherto unsolved structure of an orthorombic gamma phase of Ca(BD4)2. To properly fit the diffraction data used to solve and refine the structure of the beta phase, a preliminary structural model of the gamma phase was used. A second set of diffraction data on a sample synthesized by wet chemical method, where the gamma phase is present in significant amount, allowed us to index this phase and determine the preliminary model with space group Pbca. Ab initio calculations provide formation energies of the alpha phase and beta phase of the same order of magnitude (delta H < or = 0.15 eV). This indicates the possibility of coexistence of these phases at the same thermodynamical conditions.

Synthesis and structural properties of Nd 3− xY xFe 27.5Ti 0.8Mo 0.4(0 ⩽ x ⩽ 1.8) and Nd 3− x′ Y x′ Fe 27.8Mo 1.2(0 < x′ ⩽ 2.8) intermetallic compounds

Alkaline earth copper oxides

The polymeric compound Ni(tz)2Br2 (tz = 1,3-thiazole) has been synthesized by the addition of thiazole to an ethanolic solution of anhydrous NiBr2. Powder X-ray and neutron diffraction measurements were used for structural determination. An attempt to solve the structure using powder X-ray diffraction data was unsuccessful due to the presence of unrefinable preferred orientation, a consequence of the needle-like nature of the microcrystalline powder. The structure was determined using powder neutron diffraction data and Rietveld techniques: space group I2/a, a = 17.8854(7), b = 3.7705(2), c = 15.0919(7) A, β = 92.0007(3)°, U = 1017.13(8) A3, Z = 4. The structure consists of pseudo-octahedral units, doubly linked by halide bridges to form infinite linear chains.

Dehydrogenation reaction of Li–Mg–N–H systems studied by in situ synchrotron powder X-ray diffraction and powder neutron diffraction

High magnetic ordering temperature in the perovskites Sr4−xLaxFe3ReO12 (x=0.0, 1.0, 2.0)

Neutron diffraction evidence for a cationic order in the REMn0.5Ni0.5O3 (RE=La, Nd) and YMn0.5Co0.5O3 perovskites

Crystal structure of Mg 0.65Sc 0.35D x deuterides studied by X-ray and neutron powder diffraction

Up to now, the possible occurrence of a cationic ordering on the tetrahedral sublattices of stoichiometric double scheelite-type oxides was not settled, with somewhat contradictory X-ray diffraction and optical measurements [Blasse, G. J. Inorg. Nucl. Chem. 1968, 30, 2091]. Using two different synthesis routes, both ordered and disordered forms of fergusonite La2SiMoO8 were prepared. The crystal structure of the ordered form was determined using powder X-ray and neutron diffraction, which clearly evidence a tridimensional ordering between [SiO4] and [MoO4] tetrahedra. The crystal chemistry of ordered double sheelite-type LaIII2(SiIVO4)(MoVIO4) can be seen as an intermediate between those of simple regular scheelite or fergusonite LnIII(NbVO4) and of ordered triple scheelite BiIII3(FeIIIO4)(MoVIO4)2. The structure of the disordered La2SiMoO8 phase was analyzed using powder X-ray diffraction. A few small and larger diffraction peaks or bumps are observed in addition to the sharper peaks of a simple fergusonite cell. DIFFaX and FAULTS programs helped showing that these faint peaks originate from stacking faults between 2D ordered layers. The intermediate 2D-3D nature of SiO4/MoO4 ordering in seemingly disordered compounds might explain the previous discrepancy between optical and X-ray diffraction measurements.

Accurate structure of LiAlD4 studied by combined powder neutron and X-ray diffraction

Synthesis, structural study and magnetic properties of TbFeMnO 5

Neutron powder diffraction and magnetic phase diagram of RCo4Ga compounds (R=Y and Pr)

La1−xBixMn2O5 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) oxides are members of the RMn2O5 family. The entire series has been prepared in polycrystalline form by a citrate technique. The evolution of their magnetic and crystallographic structures has been investigated by neutron powder diffraction (NPD) and magnetization measurements. All the samples crystallize in an orthorhombic structure with space group Pbam containing infinite chains of Mn4+O6 octahedra sharing edges, linked together by Mn3+O5 pyramids and (La/Bi)O8 units. These units become strongly distorted as the amount of Bi increases, due to the electron lone pair of Bi3+. All the members of the series are magnetically ordered below TN = 25–40 K and they present different magnetic structures. For the samples with low Bi content (x = 0.2 and 0.4) the magnetic structure is characterized by the propagation vector k = (0,0,1/2). The magnetic moments of the Mn4+ ions placed at octahedral sites are ordered according to the basis vectors (Gx, Ay, 0) whereas the Mn3+ moments, located at pyramidal sites, are ordered according to the basis vectors (0, 0, Cz). When the content of Bi increases, two different propagation vectors are needed to explain the magnetic structure: k1 = (0,0,1/2) and k2 = (1/2,0,1/2). For x = 0.6 and 0.8, k2 is predominant over k1 and for this propagation vector (k2) the magnetic arrangement is defined by the basis vectors (Gx, Ay,0) and (Fx, Cy, 0) for Mn4+ and Mn3+ ions, respectively.

Transmission electron microscopy and neutron or X-ray diffraction are powerful techniques available today for characterization of the structure of various carbon materials at nano and atomic levels. They provide complementary information but each one has advantages and limitations. Powder X-ray or neutron diffraction measurements provide structural information representative for the whole volume of a material under probe but features of singular nano-objects cannot be identified. Transmission electron microscopy, in turn, is able to probe single nanoscale objects. In this review, it is demonstrated how transmission electron microscopy and powder X-ray and neutron diffraction methods complement each other by providing consistent structural models for different types of carbons such as carbon blacks, glass-like carbons, graphene, nanotubes, nanodiamonds, and nanoonions.

Domain size effects in neutron and SR powder diffraction studies of some oxides