Structural and magnetic properties of pyrochlore solid solutions (Y,Lu)2Ti2-x(Nb,Ta)xO7 ±y

D. V. West, T. M. McQueen, Q. Huang, R. J. Cava

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Abstract

The synthesis and characterization of the pyrochlore solid solutions, Y2Ti2-xNbxO7- y, Lu2Ti2-xNbxO7- y, Y2Ti2-xTaxO7- y and Lu2TiTaO7-y (-0.4<y<0.5), is described. Synthesis at 1600 °C, and 10-5 Torr yields oxygen deficiency in all systems. All compounds are found to be paramagnetic and semiconducting, with the size of the local moments being less, in some cases substantially less, than the expected value for the number of nominally unpaired electrons present. Thermogravimetric analysis (TGA) shows that all compounds can be fully oxidized while retaining the pyrochlore structure, yielding oxygen rich pyrochlores as white powders. Powder neutron diffraction of Y2TiNbO7-based samples was done. Refinement of the data for oxygen deficient Y2TiNbO6.76 indicates the presence of a distribution of oxygen over the 8b and 48f sites. Refinement of the data for oxygen rich Y2TiNbO7.5 shows these sites to be completely filled, with an additional half filling of the 8a site. The magnetic and TGA data strongly suggest a preference for a Ti3+/(Nb,Ta)5+ combination, as opposed to Ti4+/(Nb,Ta)4+, in this pyrochlore family. In addition, the evidence clearly points to Ti3+ as the source of the localized moments, with no evidence for localized Nb4+ moments.

Original languageEnglish (US)
Pages (from-to)1753-1758
Number of pages6
JournalJournal of Solid State Chemistry
Volume181
Issue number8
DOIs
StatePublished - Aug 1 2008

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Keywords

  • Magnetism
  • Oxygen deficient
  • Oxygen excess
  • Pyrochlore
  • Reduced niobium
  • Reduced titanium

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