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Journal of Materials Science

, Volume 18, Issue 1, pp 195–207 | Cite as

Mössbauer, EXAFS, and X-ray diffraction study of Fe3+ clusters in MgO:Fe and magnesiowüstite (Mg,Fe)1−xO-evidence for specific cluster geometries

  • Glenn A. Waychunas
Papers

Abstract

Mössbauer and EXAFS analysis of Fe3+-doped MgO rapidly quenched from 1200° C have yielded octahedral/tetrahedral Fe3+ site occupancy ratios which are used to place constraints on the possible defect cluster geometries. The data suggest the samples contain a range of defect aggregates consisting of combinations of basic dimer and trimer units (octahedral Fe3+ ions coupled to 1 or 2 cation vacancies) and variations about the “4-1” cluster motif. (Four cation vacancies surrounding one interstitial Fe3+.) The groupings are consistent with lattice-energy calculations for defect clusters in both FeO and MgO, the observed sample colour, and prior TEM and ED observations of defect ordering in quenched wüstite. Low-temperature annealing of the samples results in cluster growth and changes in the Mössbauer spectrum attributable to production of magnesioferritelike aggregates. The colour of the samples after annealing is indicative of grouping of magnetically interactive octahedral Fe3+ ions such as would be present in spinel nuclei. X-ray diffraction structure factor measurements of magnesiowüstite with 70 cation % Fe/(Fe+Mg) yield defect-concentration ratios similar to those observed in MgO and wüstite. This indicates that initial clustering of Fe3+ ions and cation vacancies probably results in similar structures throughout the MgO-FeO-Fe2O3 system.

Keywords

Site Occupancy Cation Vacancy Initial Cluster Sample Colour Defect Cluster 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Chapman and Hall Ltd. 1983

Authors and Affiliations

  • Glenn A. Waychunas
    • 1
  1. 1.Center for Materials ResearchStanford UniversityStanfordUSA

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