Protonated niobate/titanate pyrochlores via lead-acid exchange in Pb sub(1.5)Nb sub(2)O sub(6.5) and Pb sub(2)Nb sub(1.33)Ti sub(0.67)O sub(6.67)

Hydrogen-based niobates and niobate-titanates were derived from the pyrochlores Pb sub(1.5)Nb sub(2)O sub(6.5) (PN) and Pb sub(2)Nb sub(1.33)Ti sub(0.67)O sub(6.67) (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 sub(2.66)Pb sub(0.17)Nb sub(2)O sub(6.5).0.5H sub(2)O (HPN) and H sub(3.88)Pb sub(0.06)Nb sub(1.33)Ti sub(0.67)O sub(6.67).0.33H sub(2)O (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 sub(2)O), 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 super(-6) to 10 super(-5) S cm super(-1) for HPN and 10 super(-7) to 10 super(-6) S cm super(-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).