INVESTIGADORES
ACUÑA Leandro Marcelo
artículos
Título:
Local atomic structure in tetragonal pure ZrO2
Autor/es:
LEANDRO M. ACUÑA, DIEGO G. LAMAS, RODOLFO O. FUENTES, ISMAEL O. FÁBREGAS, MÁRCIA C. A. FANTINI, ALDO F. CRAIEVICH AND ROGÉRIO J.PRADO
Revista:
JOURNAL OF APPLIED CRYSTALLOGRAPHY
Editorial:
WILEY-BLACKWELL PUBLISHING, INC
Referencias:
Año: 2010 vol. 43 p. 227 - 236
ISSN:
0021-8898
Resumen:
The local atomic structures around the Zr atom of pure (undoped) ZrO22
nanopowders with different average crystallite sizes, ranging from 7 to 40 nm,
have been investigated. The nanopowders were synthesized by different wetchemical
routes, but all exhibit the high-temperature tetragonal phase stabilized
at room temperature, as established by synchrotron radiation X-ray diffraction.
The extended X-ray absorption fine structure (EXAFS) technique was applied
to analyze the local structure around the Zr atoms. Several authors have studied
this system using the EXAFS technique without obtaining a good agreement
between crystallographic and EXAFS data. In this work, it is shown that the
local structure of ZrO2 nanopowders can be described by a model consisting of
two oxygen subshells (4 + 4 atoms) with different ZrO distances, in agreement
with those independently determined by X-ray diffraction. However, the
EXAFS study shows that the second oxygen subshell exhibits a DebyeWaller
(DW) parameter much higher than that of the first oxygen subshell, a result that
cannot be explained by the crystallographic model accepted for the tetragonal
phase of zirconia-based materials. However, as proposed by other authors, the
difference in the DW parameters between the two oxygen subshells around the
Zr atoms can be explained by the existence of oxygen displacements
perpendicular to the z direction; these mainly affect the second oxygen subshell
because of the directional character of the EXAFS DW parameter, in
contradiction to the crystallographic value. It is also established that this model
is similar to another model having three oxygen subshells, with a 4 + 2 + 2
distribution of atoms, with only one DW parameter for all oxygen subshells.
Both models are in good agreement with the crystal structure determined by
X-ray diffraction experiments.2 nanopowders can be described by a model consisting of
two oxygen subshells (4 + 4 atoms) with different ZrO distances, in agreement
with those independently determined by X-ray diffraction. However, the
EXAFS study shows that the second oxygen subshell exhibits a DebyeWaller
(DW) parameter much higher than that of the first oxygen subshell, a result that
cannot be explained by the crystallographic model accepted for the tetragonal
phase of zirconia-based materials. However, as proposed by other authors, the
difference in the DW parameters between the two oxygen subshells around the
Zr atoms can be explained by the existence of oxygen displacements
perpendicular to the z direction; these mainly affect the second oxygen subshell
because of the directional character of the EXAFS DW parameter, in
contradiction to the crystallographic value. It is also established that this model
is similar to another model having three oxygen subshells, with a 4 + 2 + 2
distribution of atoms, with only one DW parameter for all oxygen subshells.
Both models are in good agreement with the crystal structure determined by
X-ray diffraction experiments.z direction; these mainly affect the second oxygen subshell
because of the directional character of the EXAFS DW parameter, in
contradiction to the crystallographic value. It is also established that this model
is similar to another model having three oxygen subshells, with a 4 + 2 + 2
distribution of atoms, with only one DW parameter for all oxygen subshells.
Both models are in good agreement with the crystal structure determined by
X-ray diffraction experiments.