Theoretical investigation of metastable Al2SiO5 polymorphs

Artem R. Oganov, G. David Price, John P. Brodholt

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)


Using theoretical simulations based on density functional theory within the generalized gradient approximation, a series of metastable phase transitions occurring in low-pressure Al2SiO5 polymorphs (andalusite and sillimanite) are predicted; similar results were obtained using semiclassical interatomic potentials within the ionic shell model. Soft lattice modes as well as related structural changes are analysed. For sillimanite, an isosymmetric phase transition at ca 35 GPa is predicted; an incommensurately modulated form of sillimanite can also be obtained at low temperatures and high pressures. The high-pressure isosymmetric phase contains five-coordinate Si and Al atoms. The origin of the fivefold coordination is discussed in detail. Andalusite was found to transform directly into an amorphous phase at ca 50 GPa. This study provides an insight into the nature of metastable modifications of crystal structures and the ways in which they are formed. Present results indicate the existence of a critical bonding distance, above which interatomic interactions cannot be considered as bonding. The critical distance for the Si-O bond is 2.25 Å.

Original languageEnglish
Pages (from-to)548-557
Number of pages10
JournalActa Crystallographica Section A: Foundations of Crystallography
Issue number5
Publication statusPublished - 2001
Externally publishedYes


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