Structural modulations and phase transitions in β-eucryptite

An in-situ TEM study

H. Xu, Peter J. Heaney, H. Böhm

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

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
Volume26
Issue number8
DOIs
StatePublished - Sep 1 1999

Fingerprint

phase transition
Electron diffraction
transmission electron microscopy
Phase transitions
Modulation
Transmission electron microscopy
electron
diffraction
Quartz
Order disorder transitions
Aluminosilicates
Twinning
Diffraction patterns
Electron beams
twinning
aluminosilicate
Irradiation
Ions
Fluxes
Imaging techniques

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology
  • Materials Science(all)

Cite this

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abstract = "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.",
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Structural modulations and phase transitions in β-eucryptite : An in-situ TEM study. / Xu, H.; Heaney, Peter J.; Böhm, H.

In: Physics and Chemistry of Minerals, Vol. 26, No. 8, 01.09.1999, p. 633-643.

Research output: Contribution to journalArticle

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