Reactions and phases within the TeO2-rich part of the Bi 2O3-TeO2 system: The non-equilibrium phase diagram

L. Pöppl, Zsuzsanna Szaller

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Abstract

The chemical reactions between Bi2O3 and TeO 2 oxide powder and pellets have been investigated by differential scanning calorimetry (DSC) and electron microprobe analyses applying 10°C min-1 heating and cooling rate, as well as isothermal heat treatment, respectively. The reaction pathway was identified in which the Bi 2O3 is the stationary phase and the TeO2 is the moving phase. The reaction starts by grain boundary diffusion. But at the same time, from 450°C the TeO2 evaporates onto the Bi 2O3 grains producing TeO2 layer. Melts participation in the mechanism was proved. The reaction sequence is independent of the sample composition, always the TeO2-rich phases form first. Bi2TeO5 could not be detected until the TeO2 is fully reacted. The 10°C min-1 cooling rate applied is relatively high and permits the formation of metastable phases (β-Bi 2Te4O11, Bi2Te7O 17) with cubic symmetry between 54 and 100% composition range. Though stable phases form during the subsequent heating the phase diagram has been determined under non-equilibrium conditions. In the contrast with the literature data the 54% composition is considered as the border of solid solution, from which the homogeneous and high-quality single crystal can be grown.

Original languageEnglish
Pages (from-to)375-386
Number of pages12
JournalJournal of Thermal Analysis and Calorimetry
Volume74
Issue number2
DOIs
Publication statusPublished - Nov 25 2003

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Keywords

  • BiO
  • Bismuth oxide
  • Bismuth tellurites
  • DSC
  • Phase diagram
  • Reaction mechanism

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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