R. Ben Hassen

Rietveld refinement of X-ray powder data and bond-valence calculations of NdSrNi0.5Cr0.5O4-δ compound

Compound from the solid-solution NdSrNi 1− x Cr x O 4−δ , 0≤ x ≤1, has been prepared using conventional solid-state method and was characterized by X-ray powder diffraction. The NdSrNi 0.5 Cr 0.5 O 4−δ sample shows the adoption of the K 2 NiF 4 -type structure based on the tolerance factor calculation. X-ray diffraction analysis using the Rietveld method was carried out and it was found that NdSrNi 0.5 Cr 0.5 O 4−δ compound crystallizes in tetragonal symmetry with space group I 4/ mmm . The lattice parameters are found to be at room temperature, a =3.8012(3) A and c =12.4812(1) A. For X-ray diffraction data, the reliability factors are R B =0.034, R wp =0.089, , and χ 2 =1.17. Bond-valence sum calculations were performed for nickel and chromium. The changes in unit-cell parameters are discussed in terms of oxygen stoichiometry and transition metal (3 d ) oxidation state from the perspective of the Brown bond-valence sum calculation theory.

Rietveld refinement of YbCoO3 prepared from aqueous solution-gel precursor

A polycrystalline sample of YbCoO 3 was prepared using a water-soluble complex method at relatively low temperatures. Common chelating ligands such as citric acid were employed for the synthesis of complex-based precursors, followed by thermal decomposition of the precursors at high temperatures. X-ray diffraction data were collected and the crystal structure was refined by the Rietveld method. The structure of YbCoO 3 can be described as a sesquioxide C-M 2 O 3 -like structure with space group I a -3 and unit-cell parameter a =10.4470 (2). The Yb 3+ and the Co 3+ cations are found to preferentially occupy the two nonequivalent 8 d and 24 d sites, respectively. The two independent atoms Yb/Co have octahedral coordination; however, the degrees of distortion of their coordination polyhedron are different. The relationship between the title compound and the orthorhombic Perovskite structure of YbCoO 3 reported in the literature is established.

Rietveld refinement of the gadolinium strontium oxide SrGd 2 O 4

Powder X-ray diffraction (XRD) data were collected for a new phase of SrGd 2 O 4 . Analysis using the Rietveld method was carried out and it was found that the sample crystallizes in the orthorhombic symmetry with CaFe 2 O 4 related structure. The lattice parameters are found to be a =12.0521(2) A, b =10.1327(2) A, c =3.4757(4) A and Z =4. For X-ray data R F =4.9%, R B =7.6%, R P =8.1% and χ 2 =1.51. The structure can be described as an assembly of bioctahedron [Gd 2 O 10 ] which are linked together by O 2− anions and of dodecahedron of SrO 8 .

Structural and magnetic studies of a new intermetallic compound: Er2Cu10.9Ga6.1

A new ternary phase, Er 2 Cu 10.9 Ga 6.1 , has been found in the Er-Cu-Ga phase diagram. X-ray powder diffraction data were successfully refined based on a rhombohedral Th 2 Zn 17 structure type (space group R -3 m , No. 166) with cell parameters a =8.6627(1) A, c =12.6824(2) A, and Z =3. Er 2 Cu 10.9 Ga 6.1 exhibits a paramagnetic Curie-Weiss behaviour down to 2 K with a trivalent character of Er atoms.

Crystal structure of 3-(2,2-di-bromo-acet-yl)-4-hy-droxy-2H-chromen-2-one.

In a new coumarin derivative obtained from the reaction of 3-acetyl-4-hydroxy-2H-chromen-2-one with bromine in acetic acid, the hydroxy group in involved in an intramolecular O—H⋯O hydrogen bond. In the crystal, π–π interactions between the rings of the bicycle pack molecules into stacks along the b axis.