Temperature-induced phase transition of AlPO4-moganite studied by in-situ Raman spectroscopy

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Abstract

The moganite-form of AlPO4 has recently been discovered from our high-pressure study. Similar to SiO2 - moganite, a temperature-induced displacive phase transition is expected. In order to confirm the phase transition, high-temperature in-situ Raman spectroscopy study was conducted at ambient pressure up to 600 °C. One of the low-frequency Raman modes (74 cm-1 at room temperature) significantly softened with temperature, and disappeared at 420 °C. Its frequency versus temperature relation can be well fitted with an order parameter equation, and the mode is interpreted as a soft mode with a critical exponent of 0.232(8). According to this fitting, the transition temperature is determined as 415 °C. Some hard modes also revealed slight softening or hardening with temperature up to ~ 420 °C and reached nearly constant frequency at higher temperature. Vibrational mode calculations by the first-principles density functional theory (DFT) method showed that the soft mode corresponds to tetrahedral rotations, representing the pathway of the transformation.

Original languageEnglish
Pages (from-to)126-134
Number of pages9
JournalJournal of Mineralogical and Petrological Sciences
Volume113
Issue number3
DOIs
Publication statusPublished - Jan 1 2018

Keywords

  • AlPO
  • Moganite
  • Phase transition
  • Raman spectroscopy
  • Soft mode

ASJC Scopus subject areas

  • Geophysics
  • Geology

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