Protonated niobate/titanate pyrochlores via lead-acid exchange in Pb 1.5Nb2O6.5 and Pb2Nb 1.33Ti0.67O6.67

Alicia B. Brune, Robert I. Mangham, William Petuskey

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Abstract

Hydrogen-based niobates and niobate-titanates were derived from the pyrochlores Pb1.5Nb2O6.5 (PN) and Pb 2Nb1.33Ti0.67O6.67 (PNT) by ion exchange in acid baths, affording sub-micron size white powders. The niobium sublattice was left intact, as shown by X-ray diffraction. A combination of stripping and thermogravimetric analyses gave the effective formulas H 2.66Pb0.17Nb2O6.5•0.5H 2O (HPN) and H3.88Pb0.06Nb 1.33Ti0.67O6.67•0.33H2O (HPNT). The corresponding structural refinements gave good fits to the XRD data. Densities measured by He pycnometry agreed with densities calculated from XRD analyses and the effective formulas. Thermal stability was assessed by TGA, DSC, and XRD. With increasing temperature, HPN and HPNT lost weight (H 2O), becoming amorphous, and then transforming to crystalline phases, with greatly reduced particle size. HPN was more stable than HPNT. The electrical conductivities of powder compacts in wet atmospheres were moderate and attributed mainly to proton conduction; i.e., 10-6 to 10 -5 S cm-1 for HPN and 10-7 to 10-6 S cm-1 for HPNT (from room temperature to 230 °C). Experimental results were interpreted in terms of Nb(V) being a stronger electron acceptor than Ti(IV).

Original languageEnglish (US)
Pages (from-to)621-634
Number of pages14
JournalJournal of Materials Science
Volume43
Issue number2
DOIs
StatePublished - Jan 1 2008

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ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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