Materials Science Forum Vols. 443-444

Abstract: Ni₇(C₄H₄O₄)₄(OH)₆(H₂O)₃ . 7H₂O, a new layered nickel(II) succinate, was prepared hydrothermally (180°C, 48 h, autogenous pressure) from a 1:1.5:4.1:120 mixture of nickel (II) chloride hexahydrate, succinic acid, potassium hydroxide and water. It crystallizes in the monoclinic system (space group P2₁/c, Z = 4) with the following parameters a = 7.8597(1) Å, b = 18.8154(3)Å, c = 23.4377(4) Å,ϐ = 92.0288(9)°, and V = 3463.9(2) Å ₃. Its structure, which contains 55 non-hydrogen atoms, was solved ab initio from synchrotron powder diffraction data. It can be described from hybrid organic-inorganic layers, constructed from nickel oxide corrugated chains. These chains are built up from NiO₆ hexameric units connected via a seventh octahedron. Half of the succinates decorate the chains, and the others connect them to form the layers. The three dimensional arrangement is ensured by hydrogen bonds directly between two adjacent layers and via free water molecules.

Abstract: The structure of a high ionic conductor Rb₄Cu₁₆I_7.2Cl_12.8 at low temperature has been reinvestigated by use of angle-dispersive neutron powder diffraction. All the diffraction data have been analyzed with integrated software REMEDY consisting of RIETAN-2000 for whole-pattern fitting and MEED for calculating densities of electrons or atomic nuclei by the maximum-entropy method. The resulting nuclear-density maps have reconfirmed that Cu1-Cu2 chains are the main conduction pathways in this material, as previously suggested from the Rietveld analysis of neutron powder diffraction data.

Abstract: A recent measurement on the high-pressure phase of Ca(OH)₂ using high-resolution synchrotron X-ray powder diffraction has been carried out on a hydrogenated sample at high-temperature. It complements an earlier time-of-flight neutron measurement carried out in the US on a deuterated sample at low temperature. The two protons are found by Rietveld refinement using a new suitable non-Fourier based strategy, for which GSAS and FullProf yield very similar results. Our X-ray result agrees with the previous neutron study for one proton site only, prompting us to reinvestigate the neutron data. A second new and distinct non Fourier-based strategy coupled with GSAS is used to tackle the latter data and indeed confirms the US results. Whilst the reasons for this X-Ray vs Neutron discrepancy can only be guessed at this stage, the use of the two related proton-finding strategies could be extended beyond our specific study.

Abstract: The crystal structure of new Prussian blue analogue samples, KCu[Fe_1-x Co_x(CN)₆], KNi[Fe_1-x Co_x(CN)₆] and Fe[Fe_1-x Co_x(CN)₆], was solved on the base of the model from Keggin and Miles [1] and refined by the Rietveld method [2] from conventional X-ray powder diffraction data. These compounds form mixed crystals for all Fe/Co ratios. The crystal structure of the KCu[Fe_0.3Co_0.7(CN)₆], KNi[Fe_0.3Co_0.7(CN)₆] and Fe[Fe_0.8Co_0.2(CN)₆] is presented in detail. For both potassium containing compounds the disorder in the potassium arrangement is the most obvious characteristic.

Abstract: Pd₃P, which crystallises in the cementite, Fe₃C-type structure, forms a solid solution with nickel. The crystal structure contains two crystallographically different palladium sites (8d and 4c). Refinements of neutron powder diffraction intensities using the Rietveld method show that all nickel atoms occupy the eight-fold position. The unit cell parameters were refined to a=5.7812(4) Å, b=7.4756(6) Å and c=5.1376(4) Å, for Pd_2.7Ni_0.3P_0.94.

Abstract: We have performed neutron powder diffraction (NPD) experiments on polycrystalline powders with nominal compositions (Ca_0.5La_0.5)(Ba_1.25La_0.75)Cu₃O₇- δ , (Ca_0.6La_0.4)(Ba_1.15La_0.85)Cu₃O₇-δ and (Ca_0.8La_0.2)(Ba_0.95La_1.05)Cu₃O₇-δ . The diffraction patterns, analysed by the Rietveld method, show that all samples consist mainly of a tetragonal Y-123 type phase. Unit cell parameters a and c shorten as the calcium content increases: a = 3.8660(2), 3.8634(3), and 3.8624(5) Å; c = 11.6325(11), 11.6143(14), and 11.5822(20) Å for x-values 0.5, 0.6, and 0.8, respectively. For the x = 0.6 and 0.8 samples the Rietveld refinement of calcium occupancies and EDX analysis suggest that the actual composition is closer to x ≈ 0.5. However, since the lattice parameters do change, it is also suggested that at these higher doping levels calcium does enter the Y- site to a larger extent than for the x = 0.5 composition. This is also in accordance with previously reported values for the T_c, which decreases slighty as x changes from 0.5 to 0.6 and has a pronounced change from 80 K to 73 K for x = 0.6 and 0.8, respectively.