Determination of the fluorite related structure of Mn3Ta2O8, using synchrotron X-ray powder and electron diffraction data

(Note: The full text of this document is currently only available in the PDF Version )

Saeid Esmaeilzadeh, Jekabs Grins and Andy Fitch


Abstract

The Mn2+-containing oxide Mn3Ta2O8 has been synthesised at 1200°C in Ar atmosphere, and its structure has been solved from X-ray synchrotron powder data (λ0.65 Å) by direct methods. The structure was refined by the Rietveld method to RF=6.3%, with space group I41/a, a=11.2728(2), c=9.8030(3) Å, V=1243.47 Å3, from 1190 reflections with d≥0.65 Å. It is related to the fluorite structure with a≊√5af and c≊2af. The Ta atoms are octahedrally coordinated by oxygen atoms and the three crystallographically different Mn atoms by 7, 4 + 4 and 4 oxygen atoms. Electron diffraction patterns show the presence of weak superstructure reflections corresponding to a primitive unit cell with a′=a and c′=6c. The melting point of Mn3Ta2O8 is 1470°C in Ar atmosphere. It is a semiconductor with an activation energy of 1.2 eV and a conductivity σ=3.7×10–5 S cm–1 at 600°C. The magnetic susceptibility shows a maximum at 23 K and a Curie-Weiss behaviour at higher temperatures, with µeff=5.7(1) µB per Mn atom. When Mn3Ta2O8 is oxidised at 1100°C in air an Mn-Ta oxide forms, which has a wolframite type structure with unit cell a=4.7574(5), b=5.7296(6), c=5.1133(4) Å and β=91.202(9)°.


References

  1. A. C. Turnock, J. Am. Ceram. Soc., 1966, 49, 382 Search PubMed.
  2. N. Schönberg, Acta Metall., 1955, 3, 14 Search PubMed.
  3. J. Grins, P.-O. Käll and G. Svensson, J. Solid State Chem., 1995, 117, 48 Search PubMed.
  4. J. Grins and A. Tyutyunnik, J. Solid State Chem., 1998, 137, 276 Search PubMed.
  5. M. A. Subramanian, G. Aravamudan and G. V. Subba Rao, Prog. Solid State Chem., 1983, 1, 55 Search PubMed.
  6. R. Norrestam, Ark. Kemi, 1968, 29, 343 Search PubMed.
  7. G. Cascarano, L. Favia and C. Giacovazzo, J. Appl. Crystallogr., 1992, 25, 310 Search PubMed.
  8. A. C. Larson and R. B. Von Dreele, Los Alamos National Laboratory Report No. LA-UR-86-748, 1987.
  9. T. Hörlin, Chem. Scr., 1985, 25, 270 Search PubMed.
  10. P.-E. Werner, L. Eriksson and M. Westdahl, J. Appl. Crystallogr., 1985, 18, 367 Search PubMed.
  11. I. D. Brown and D. Altermatt, Acta Crystallogr., Sect. B, 1985, 41, 244 Search PubMed.
  12. R. D. Shannon, Acta Crystallogr., Sect A, 1965, 32, 258 Search PubMed.
  13. H. Weitzel, Z. Kristallogr., 1976, 144, 238 Search PubMed.
  14. S. Esmaeilzadeh, J. Grins and A.-K. Larsson, in preparation.
Click here to see how this site uses Cookies. View our privacy policy here.