GAUSS-LORENTZ SIZE-STRAIN BROADENNING AND CELL PARAMETERS ANALYSIS OF Mn DOPED SnO2 PREPARED BY ORGANIC ROUTE
Carlos O. Paiva-Santos, Helder Gouveia, Wanda Las, Jose Arana Varela
Dep. Físico-Química,
Instituto de Química - UNESP, R. Prof. Francisco Degni s/n., 14800-900 Araraquara SP
Brazil
Email: copsanto@iq.unesp.br
Keywords: Crystallite size, microstrain,
lattice parameters
SnO2 samples doped with x-mol% Mn (x
= 0, 0.3, 0.5, 0.7, 1.0) were prepared by organic route, calcined
at 800oC for 4h, and characterized by the Rietveld
method with X-ray diffraction data. The Thompson-Cox-Hastings
pseudo-Voigt profile function was used as it is in the DBWS 9411
Rietveld analysis software. For the FWHM, were refined only the
Gauss and Lorentz coefficients that can be related to size and
strain, while the others were kept fixed in the values reached
for a WC standard. The Gauss-strain, Lorentz-size and
Lorentz-strain broadening coefficients present an almost uniform
variation in respect to the Mn inclusion while the Gauss-size
coefficient vary disorderly. The crystallite size determined with
these coefficients varies uniformly for Lorentz broadening and
higly non-uniform for Gauss broadening. The strain determined
with the Lorentz coefficient are approximately 5 times smaller
than when determined with Gauss coefficient.. The Lorentz and
Gauss contributions for crystallite size (also for strain) were
weighted in the FWHM formulae of the TCHZ pseudo-Voigt profile
function, and used in the evaluation of the mean crystallite
size. The crystallite size and strain so determined showed a
uniform decrease in the crystallite size and increase in the
microstrain with the addition of dopants. It was also observed
that the unit cell volume decreases slightly as the amount of
added dopant increases. For undoped sample the cell parameters
are a = 4.73785(5) A and
c = 3.18667(4) A and
for 1mol% Mn doped SnO2 the cell parameters are a
= 4.73577(7) A and c = 3.18481(6) A.
Based on the cell parameters' variation it is suggested that the
Mn dopant occupies the same crystallographic site as Sn, in the
SnO2 crystal structure. Considering that the
crystallite size decreases with increasing Mn content, this could
explain Mn segregation on the grain boundary of sintered samples
and the increase in conductivity observed elsewhere.
Acknowledgments: This work was performed with financial support from FAPESP and CNPq.