A new polymorph of eucryptite (LiAlSiO4), ε-eucryptite, and thermal expansion of α- and ε-eucryptite at high pressure

Jianzhong Zhang, Aaron Celestian, John B. Parise, Hongwu Xu, Peter J. Heaney

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22 Scopus citations

Abstract

X-ray diffraction experiments have been carried out on β-eucryptite (LiA1SiO4) at pressures up to 2.5 GPa and temperatures up to 1073 K in a large-volume apparatus. With room-temperature compression, we observed a phase transition to a new polymorph between 0.83 and 1.12 GPa. This transition is reversible in character. The new phase, referred to here as ε-eucryptite, can be indexed according to an orthorhombic unit cell with a = 10.217(4) Å, b = 8.487(4), Å, c = 5.751(3) Å, and V = 498.7(4) Å3 for XRD data at 2.2 GPa and 298 K. On heating at 2.2 GPa, ε-eucryptite and β-eucryptite were metastable over the temperature interval 298-873 K; at higher temperatures they underwent an irreversible phase transition to α-eucryptite. Both hexagonal α-eucryptite and ε-eucryptite show anisotropic thermal expansion. For α-eucryptite, we obtained αa = 6.71(±0.25) × 10 6 K-1, αv = 1.07(±0.05) × 10-5 K-1, and αv = 2.42(±0.1) × 10-5 K-1 at 1.94(2) GPa over the temperature range 298-1073 K. For ε-eucryptite at 2.32(8) GPa, we find larger thermal expansion in a smaller temperature range 298-773 K. with αa = 1.47(±0.15) × 10-5 K1, αb = 6.65(±1.33) × 106 K-1, αc = 7.83(±0.88) × 10-6 K-1, and αv = 2.99(±0.15) × 10-5 K-1. In combination with a previous determination of thermal expansion at ambient pressure, the pressure effect on volume thermal expansion of α-eucryptite is determined to be -2.68 x 10-6 GPa-1 K-1, and the temperature derivative of the bulk modulus is estimated to be -0.015 GPa/K.

Original languageEnglish (US)
Pages (from-to)566-571
Number of pages6
JournalAmerican Mineralogist
Volume87
Issue number4
DOIs
StatePublished - Jan 1 2002

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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