Electrical and catalytic properties of some oxides with the fluorite or pyrochlore structure

Abstract

The catalytic properties of mixed oxides with the fluorite or pyrochlore structure were investigated using CO oxidation. The presence of ions with a variable valence state, the size of the ions and especially the extent of pyrochlore ordering affect kinetic behaviour and activity of the investigated materials.

Powder Diffraction Data for the Imperfect Pyrochlore Terbium Titanate, Tb2Ti2O7

“…The lattice parameter is supposed to follow Vegard's law with the terbium content. This would explain the apparent deviations in the reported values of this parameter in literature and it would also explain the deviations found in the reaction rate of the catalytic oxidation of CO (Korf et at, 1987, ter Maat et al, 1984. We present in this paper the powder diffraction pattern of Tb 2 Ti 2 O 7 , the correct value of the lattice parameter and the least-squares evaluation of the intensities in relation to longrange ordering of mainly cations.…”

“…The catalytic oxidation of carbon monoxide is favored by a partial conversion of a compound with a fluorite structure into a compound with a pyrochlore structure (Korf et al, 1987). Some bismuth or terbium compounds (ter Maat et al, 1984) also show such catalytic activity. Incorporation of terbium introduces an increasing contribution of electronic conductivity of the compound, caused by the redox couple Tb 3+ /Tb 4+ (van Dijk, 1985).…”

Synthesis and structural characterization of a series of lanthanide stannate pyrochlores

“…They act as potential panacea for the material research fields [2], such as metal-semiconductor transitions [3,4], magnetic frustration/spin ices [5][6][7], colossal magnetoresistance [8], superconductivity [9], ferroelectrics, mixed conductivity [10], pigments and catalysis [11][12][13].…”