Dimorphism in methylammonium aluminum alum studied by X-ray diffraction and electron paramagnetic resonance

Ssu Hao Lou, Jiang-Tsu Yu

Research output: Contribution to journalArticle

Abstract

We have found a reliable method of growing single-phase methyl-ammonium alum (MASD) crystallising in the infrequently-occurring α alum structure; the presence of the perchlorate ion, ClO4 -, in growth solutions induces the crystallisation of α MASD crystals. Seeding the growth solution with α MASD crystals also induces crystallisation of new α MASD crystals. The X-ray powder diffraction pattern and the EPR spectrum of the Cr3+ ions doped into α MASD are drastically different from those for the more frequently occuring β MASD. The linewidths of Cr3+ in α and β MASD show anomalous angular dependence. The inhomogeneous line broadening observed for β MASD could be explained by a random distribution in the orientation of the symmetry axis of the trigonal [Cr(H2O)6]3+ complex. The linewidth anomaly shows a more complicated angular dependence for α MASD; it could be that not only the orientation of the symmetry axis but also the magnitude of the axial crystal field of [Cr(H2O)6]3+ suffer random distributions.

Original languageEnglish
Pages (from-to)775-779
Number of pages5
JournalSolid State Communications
Volume84
Issue number7
DOIs
Publication statusPublished - 1992 Jan 1

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Materials Chemistry

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