Some properties of zirconates and stannates with the pyrochlore structure

Abstract

The properties of the stannates and zirconates (M2Sn2O7 and M2Zr2O7) of yttrium, lanthanum, cerium and neodymium are discussed, and the materials are considered for possible application in magnetohydrodynamic (MHD) power generation. Measurements are discussed of their structural properties, thermal expansion, thermal diffusivity, electrical resistivity, resistance to oxidation, to chemical corrosion, and to electrolytic corrosion. Thermal shock resistance is also qualitatively assessed. For non-electrical applications, lanthanum stannate has shown the most promise, especially in the corrosion tests. All the materials are insulators below 1000 K, except cerium zirconate which has ample electrical conductivity (> 10 Ω−1 m−1 above 1400 K) for use as an MHD electrode. Cerium zirconate has complicated structural and electrical properties, and must be prepared in low oxygen partial pressures. However, it is easily oxidized and may disintegrate. The equimolar ceria-zirconia solid solution formed when the oxides are fired in air would be more useful as an MHD material.