Order-disorder in R3TaO7 (R=rare earth) phases

Yoshiyuki Yokogawa, Masahiro Yoshimura, Shigeyuki Somiya

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A series of 3R2O3·Ta2O5 (R3TaO7, R=rare earth) samples were synthesized in various conditions; i.e. solid-state reactions at 1350°C or 1700°C, melting and cooling, rapid quenching of the melt and annealing at 1700°C, etc. According to powder X-ray diffraction, the crystal structure of R3TaO7 is more symmetric and disordered for the smaller ionic radius of the R3+ ion, changing from weberite-type orthorhombic to pseudo-cubic to pyrochlore-type cubic to fluorite-type cubic. We prepared a series of R3TaO7 single crystals by a floating-zone method for further investigation of R3TaO7 structures. Although the powder X-ray diffraction patterns of R3TaO7 showed a cubic fluorite structure for the smaller R3+ ions, single-crystal X-ray diffraction gave diffraction spots forbidden by the fluorite face-centered-cubic structure. This observation shows that the R3+ and Ta5+ ions are ordered in R3TaO7 even for the smaller R3+ ions.

Original languageEnglish
Pages (from-to)1250-1253
Number of pages4
JournalSolid State Ionics
Issue numberPART 2
Publication statusPublished - 1988 Sep

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics


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