Protonated niobate/titanate pyrochlores via lead-acid exchange in Pb1.5Nb2O6.5 and Pb2Nb1.33Ti0.67O6.67

• Published in: Journal of materials science 2008, Vol.43 (2), p.621-634
• Main Authors: Brune, Alicia B, Mangham, Robert I, Petuskey, William T
• Format: Article
• Language: English
• Subjects: ambient temperature; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; diffraction; Elements and non-metal compounds (oxides, hydroxides, hydrides, sulfides, carbides, ...); Exact sciences and technology; Inorganic chemistry and origins of life; Ion exchange; Materials Science; Niobates; Niobium; particle size; Polymer Sciences; Powder compacts; powders; Preparations and properties; Proton conduction; Pycnometry; Pyrochlores; Room temperature; Solid Mechanics; Stability analysis; temperature; Thermal stability; thermogravimetry; Titanates; titanium; X-ray diffraction
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-007-2170-0

Hydrogen-based niobates and niobate-titanates were derived from the pyrochlores Pb₁.₅Nb₂O₆.₅ (PN) and Pb₂Nb₁.₃₃Ti₀.₆₇O₆.₆₇ (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 H₂.₆₆Pb₀.₁₇Nb₂O₆.₅·0.5H₂O (HPN) and H₃.₈₈Pb₀.₀₆Nb₁.₃₃Ti₀.₆₇O₆.₆₇·0.33H₂O (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 (H₂O), 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).