A MÖSSBAUER EFFECT STUDY OF THE
QUADRUPOLE INTERACTION IN
PARAMAGNETIC CHLORINE AND FLURINE
CONTAINING β-FeOOH
D. Chambaere, A. Govaert, E. De Grave, G. Harts, G. Robbrecht
To cite this version:
D. Chambaere, A. Govaert, E. De Grave, G. Harts, G. Robbrecht. A MÖSSBAUER EFFECT
STUDY OF THE QUADRUPOLE INTERACTION IN PARAMAGNETIC CHLORINE AND
FLURINE CONTAINING β-FeOOH. Journal de Physique Colloques, 1979, 40 (C2), pp.C2350-C2-352. <10.1051/jphyscol:19792124>. <jpa-00218495>
HAL Id: jpa-00218495
https://hal.archives-ouvertes.fr/jpa-00218495
Submitted on 1 Jan 1979
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JOURNAL DE PHYSIQUE
Coiloque C2, suppldment au n o 3, Tome 40, mars 1979, page
~2-350
A MbSSBAUER EFFECT STUDY OF THE QUADRUPOLE INTERACTION I N PARAMAGNETIC CHLORINE AND
F L U 3 R I N E CONTAINING B-FeOOH
D. Chambaere, A. Govaert, E. de Grave, G. Harts and G. Robbrecht
Laboratory of Magnetism, University of Ghent, Proeftuinatraat 86, B-9000 Ghent, Belgium
Rdsum6.- Des ichantillons de 0-FeOOH contenant des ions de chlorure et fluorure ont 6tL dtudids par
microscopic Llectronique, diffraction de rayons X et spectroscopie Mb'ssbauer. L'apparance macroscopique des cristaux, ainsi que leurs propridt6.s microscopiques diffsrent beaucoup d'une variitL P
l'autre. On sugg2re que, les ions de chlorure n'occupant que les trous de la maille Llimentaire, les
ions de fluorure peuvent aussi substituer des OH dans les octasdres O/OH.
Abstract.- Chlorine and fluorine containing 8-FeOOH samples are studied by electron microscopy,
Rkgendiffraction and Mb'ssbauer spectroscopy. The macroscopic shape of the crystals, as well as
their microscopic properties are found to be very different for both varieties. It is suggested that,
while chlorine ions only occupy the holes exhibited by the unit cell, fluorine ions might also substitute OH'S in the O/OH octahedra.
In a previous paper /I/, we reported the influence of the chlorine ions on the quadrupole inte-
Figure la shows a typical 8-PeOOH(C1) MSssbauer
spectrum at room temperature.
raction in paramagnetic 8-FeOOH (further denoted
8-FeOOH(C1)).
" ~ e MEssbauer effect measurements on
an expanded velocity scale revealed the presence of
two strongly overlapping doublets, the area ratio of
which could be related to the chlorine content, determined by 37~1-neutronactivation analysis.
Fluorine containing 0-FeOOH (further denoted
by 8-FeOOH(F)) has been prepared by hydrolysis of a
0.1 M FeF3 solution at temperatures ranging from
40Dc to 100°C. The obtained compounds were studied
by electron microscopy, Riintgendiffraction and Mijssbauer spectroscopy. The experimental set-up is described elsewhere /I/.
Electron microscopy on 8-FeOOH(C1) reveals
typical cigar shaped crystals and clearly shows that
these somatoids are built up of parallel tubular rods
discovered by Feitknecht /2/ and further studied by
e.g. Watson et al. /3/ and Gallagher 141. On the
other hand electron micrographs of 0-FeOOH(F) reveal
crystals compressed along the long axis (c-axis) and
in which the above mentioned superstructure is not
detectable.
X-ray diffraction on 0-FeOOH(C1) shows the
same pattern as described by Mackay /5/, but yields
slightly larger values of the tetragonal lattice
Fig. 1 : Mgssbauer spectrum of 8-FeOOH(C1) (a) and
8-FeOOH(F) (b) at room temperature. Dots represent
experimental data. The best fit and its constituent
Lorentzian lines are drawn in full line.
The spectra can satisfactorily be described as a
superposition of two Lorentzian shaped doublets,
denoted the low distortion (LD) and high distortion
parameters : a = 10.54 t 0.02
and c = 3.033 + 0.002 i. (HD) doublet /I/. Figure Ib shows a Mb'ssbauer specFor 8-FeOOH(F) we calculate values of a = 10.44
trum of 0-FeOOH(F). One can inrmediately notice, even
0
0
without fitting the spectrum, that the absorption
0.03 A and c = 3.02650.005 A which are consistent
*
with the lattice parameters of both varieties, repor
ted by Keller 161.
envelope of the 8-FeOOH(F) spectrum is broader than
that of the 8-FeOOH(C1) spectrum. The only reasonable-
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792124
way of fitting this spectrum with Lorentzian lines
cular quadrupole interaction.
In this case we can write down the following
is by introducing a third doublet. This yields logical variations of isomer shift and quadrupole split-
formulae for both compounds :
ting throughout the paramagnetic temperature region.
Fe808(OH-) (C1-, OH-)
<2
while a two doublet fit introduces inconsistencies
and
in the obtained results.
F-
(F-, OH-)
(O<Y<1)
<2
The quadrupole splitting of the two innermost
doublets is close to the value observed in 6-FeOOH
The charge compensating hydrogen ions are omitted
(Cl) (table I).
and the halogen ions between brackets are those lo-
The existence of the third doublet
is somewhat enigmatic. It exhibits a very large qua-
cated in the holes of 0-FeOOH's hollandite type
drupole splitting, in fact beyond the usually cited
structure /5,6/.
range for Fe3+ in octahedral coordination 171.
Another argument in favour of anion exchange
in 6-FeOOH(F) are thesurprisingly high fluorine contents which we determined by "F-neutron
activation
analysis. The maximum chlorine content observed is
8.17 weight XC1. Arranging one C1-ion in each available halogen ion site (the holes exhibited by the
unit cell) yields a maximum occupancy of 82% of the
holes. On the other hand calculation learns that a
100% occupancy of the holes by F-' ions would lead to
a fluorine content of 5.34 weight X F. Still, the
minimum fluorine content measured in our samples
amounts to 7.36 weight % F (corrected for excess
water).
This excess of F- ions possibly substitutes
OH- ions in the O/OH octahedra.
Furthermore, it is impossible, contrary to the
Experimental values of quadrupole splitting and isomer shift (referred to Pd) for both varieties. The
numbers in brackets denote the region in which parameter values for different samples (7 for each variety) are observed, not the experimental errors.
ved fluorine content. This again suggests a more
Its linewidth decreases with decreasing hydrolysis-
continuous approach to the ~assbauerabsorption envelope, because introducing still more discrete d o w
temperature from 0.30nrm. s-' for a sample prepared
blets would increase the uncertainty on the inten-
at 100°C to 0.23mm.s-'
sities and make their obtained values physically
for a sample prepared at 40°C,
i.e. below the experimentally observable limit.
One explanation for this doublet could be that
the spectra of 6-FeOOH(F)
can no longer be fitted
with a sum of Lorentzian lines, this procedure being
case of 6-FeOOH(Cl),
to straightforwardly correlate
the intensities of the Msssbauer lines to the obser-
irrelevant.
The problem of both B-FeOOH's varieties surely
merits further investigation. From the data reported
above, it follows already, be it only qualitatively,
only an approximation, but need an analysis invol-
that the kind of halogen ion involved in the forrna-
ving complete transmission integrals as described by
tion of this oxyhydroxide very much influences its
e.g. Dunham et al. 181.
crystallization and its chemical and physical pro-
Another possibility is that the 6-FeOOH(F)
perties.
spectrum originates from a more continuous distribution of quadrupole interactions than that of
FeOOH(Cl),
B-
because more F- than C1- configurations
Acknowledgements.- Pr. Dr. J. Hoste is acknowledged
for his kind permission to perform the neutron acti-
around an iron atom are possible. Indeed, since the
vation analysis in his laboratory. We also wish to
ionic radius of F- is approximately equal to that
thank Dr. R. Cornelis and Dr. P. Vanacker for their
of OH-, the latter ion might be substituted by the
assistance at these analyses. The authors are indeb-
former within the OIOH octahedra themselves, while
ted to I.W.O.N.L.
this is highly improbable for the much larger C1ion. This would greatly increase the possible nuder
of iron surroundings, each giving rise to its parti-
and F.K.F.O.
for financial support.
JOURNAL DE PHYSIQUE
References
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Chambaere, D., Covaert, A., d e S i t t e r , J . , d e
Grave, E., S o l i d S t a t e Conrmun. 26 (1978) 657.
/ 2 / F e i t k n e c h t , W., Fourth I n t e r n . Symp. R e a c t i v i t y
i n S o l i d s , E l s e v i e r , Amsterdam (1960) 579.
/ 3 / Watson, W., C a r d e l l , R.,
Chem. 66 (1962) 1757.
/4/ G a l l a g h e r , K . ,
Nature
Heller, W.,
226
151 Mackay, A . , Miner. Mag.
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