Structural study of zinc-substituted nickel hydroxides

The structure of zinc-substituted nickel hydroxide is investigated as a fun ction of the amount of zinc. The hydroxide shows a beta-type structure with up to 10% zinc in substitution for nickel (in mol), whereas an alpha-type phase is stabilised with 20-50% zinc. For the beta-type phases, the unit ce ll parameters are similar to those of the non-substituted phase. The X-ray diffraction patterns evidence the presence of stacking faults. Zinc cations are located in octahedral sites of the slab in substitution for nickel. Fo r the alpha-type phases (d(interslab) = 8.4 Angstrom), EXAFS spectroscopy g ives evidence that the zinc cations are located in tetrahedral sites of the interslab space, these tetrahedra share one face with the octahedral vacan cies within the slab. Mass spectrometry coupled with thermogravimetric anal ysis together with chemical analysis show the presence of carbonate ions in this phase. These anions are monodendate as evidenced by IR spectroscopy. The existence of pairs of zinc cations located above and below the octahedr al vacancies of the slab can be considered. This implies an excess of posit ive charge which is compensated by the intercalation of carbonate ions. How ever, the turbostratic character of the alpha-type phase allows the coexist ence of other local configurations within the structure.