STRUCTURAL AND QUANTITATIVE PHASE ANALYSIS OF Zn7-xNixSb2O12 PREPARED BY POLIMERIC PRECURSORS
Lucianna Gama1, Carlos O. Paiva-Santos2, Marcos A. L. Nobre 1, José A. Varela2, Elson Longo1
1 Lab. Interdisciplinar de
Eletroquímica e Cerâmica - Univ. Federal de Sao Carlos - Depto.
de Química, Cx. Postal 676 - 13565-905 - Sao Carlos - SP
(Brazil).
lucianna@iris.ufscar.br
2 Instituto de Química - Universidade
Estadual Paulista, Araraquara - SP (Brazil).
The Zn7Sb2O12 are known by
crystallizing in inverse spinel type structure, in which 8 of the
tetrahedral positions are occupied by Zn2+ and 16 of
the octahedral positions are randomly occupied by Sb5+
and Zn2+. Samples of Zn7Sb2O12
were synthesized by the method of the polymeric precursors
developed by Pechini and doped with nickel (phase Zn7-xNixSb2O12,
x = 0.8, 1, 2, 3 and 4). The resulting powders were calcined at
1000°C by 1 hour and then characterized by infrared spectroscopy
and the Rietveld method with XRD data. The IR analyses indicated
that Ni was just substituting Zn in the octahedral site for x
< 2 and also substituting the tetrahedral site for x >=2.
Those observations were considered in the refinements by the
Rietveld method. In the refinements for x >=2 a bimodal
distribution of crystallite size was observed. The occupation of
the tetrahedral site by Ni occurred preferentially in the portion
of material with smaller crystallites. It was verified that the
unit cell volume decreases with the increase of added Ni. For the
Zn7Sb2O12 the volume is
636.27(4) A3 and for Zn3Ni4Sb2O12
the volume is 617.81(7) for the smallest crystallites and
618.3(4) for the smallest crystallites. According the difference
in the unit cell volume between the largest and smaller
crystallites, it is supposed that the fraction of the material
with smaller crystallites is the one, which preferentially absorb
Ni in the tetrahedral site.
Acknowledgements: The authors are grateful to CNPq, CAPEs
and FAPESP, all Brazilian agencies, for supporting this work.