>Is it possible to distinguish the valence state of an ion, say manganese,
>in different compounds of the same structure (say LiMn2O4 from
>Li0.3Mn2O4, both Fd3m) using x-ray powder diffractometry?
I doubt you can do that with ordinary X-ray diffraction. There are two
possible approaches to determining oxidation states. A quick search of
my references gives the following:
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1) Rietveld refinement with synchrotron radiation near resonance energies
eg the following may be relevent (from ICSD for WWW)
1. Will, G. (1981) Fortschritte der Mineralogie; Acta Crysta . 59 , 31.
Energiedispersion und Synchrotronstrahlung: Eine neue Methode und eine
neue Strahlenquelle fuer die Roentgenbeugung .
2. Lightfoot, P., Cheetham, A. K. and Sleight, A. W. (1987) Inorganic
Chemistry. 26 , 3544.
Structure of MnPO4 (H2O) by Synchroton X-Ray Powder Diffraction .
3. Wilkinson, A. P., Cheetham, A. K., Tang, S. C. and Reppart, W. J. (1992)
Journal of the Chemical Society. Chemical Communications . 1992 , 1485.
Cation Distribution in Zeolite Zinc/Sodium-Y by Resonant X-Ray Diffraction .
4. Sinclair, D. C., Aranda, M. A. G., Attfield, P. and Rodriguez-Carvajal, J.
(1994) Physica C . 225 , 307.
Cation distribution and composition of the Tl-2223 superconductor from
combined powder neutron and resonant X-ray diffraction .
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2) Rietveld refinements with NEUTRON data to give more accurate bond
lengths, then Zachariasen/Brown/Shannon bond charge calculations.
(We used this method extensively for superconductor structures in the 80's).
For some recent neutron work on LixMn2O4 see (again from ICSD for WWW):
1. David, W. I. F., Thackeray, M. M., De Picciotto, L. A. and Goodenough, J. B.
(1987) Journal of Solid State Chemistry. 67 , 316.
Structure refinement of the spinel-related phases Li2 Mn2 O4 and Li.2 Mn2 O4 .
2. Fischer, D. and Hoppe, R. (1993) Zeitschrift fuer Anorganische und Allgemeine
Chemie. 619 , 1419.
Koordinationszahl 4 oder 6 fuer Lithium?: Die Kristallstruktur von wasserfreiem Lithiumpermanganat, Li(MnO4) .
3. Thackeray, M. M., de Kock, A. and David, W. I. F. (1993) Mat. Res. Bull. 28,1041.
Synthesis and structural characterization of defect spinels in the
lithium-manganese-oxide system .
4. Fong, C., Kennedy, B. J. and Elcombe, M. M. (1994) Zeit. f. Krist. 209 , 941.
A powder neutron diffraction study of -lambda and -gamma manganese dioxide
and of Li Mn2 O4 .
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Alan Hewat, ILL Grenoble, FRANCE <hewat@ill.fr> tel (33) 4.76.20.72.13
ftp://ftp.ill.fr/pub/dif fax (33) 4.76.48.39.06 http://www.ill.fr/dif/