Structural modulations and phase transitions in β-eucryptite: An in-situ TEM study

H. Xu, P. J. Heaney, H. Böhm

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18 Scopus citations


Beta-eucryptite as grown by the flux method has been investigated by in-situ cold- and hot-stage transmission electron microscopy (TEM). Using electron diffraction and dark-field TEM imaging, we found no evidence for the merohedral twinning that accompanies structural collapse at the β-to-α-quartz transition, suggesting a true hexagonal symmetry for the aluminosilicate framework of β-eucryptite. Selected-area electron diffraction (SAED) patterns exhibited a variety of incommensurate structures along the three a axes with an average modulation period of about 6.5 a. These modulated structures arise from superperiodic stacking parallel to (100) of two structural units with different Li configurations. In-situ heating experiments show that the modulated structures undergo a reversible transition to the disordered modification at elevated temperatures. This transition arises from positional order-disorder of Li ions along the main structural channels. In addition, it appears that at constant low temperature, electron beam irradiation alone can induce a sequence of transitions similar to those that are thermally induced from the ordered modification to modulated states.

Original languageEnglish (US)
Pages (from-to)633-643
Number of pages11
JournalPhysics and Chemistry of Minerals
Issue number8
StatePublished - Sep 1 1999

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Geochemistry and Petrology

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