abstract
Terbium hafnate and zirconate ceramics with submicron grain sizes were prepared via mechanically-activated synthesis. X-ray and electron diffraction and infrared (IR) absorption spectroscopy showed that TbZrO4-delta has a disordered fluorite-type structure, while TbHfO4-delta is partially ordered, containing pyrochlore microdomains. The oxygen ion transference numbers determined by the modified e. m. f. technique under oxygen/air gradient, vary in the range 0.08-0.26 at 873-1123 K, increasing with temperature. The activation energies for ionic and p-type electronic transport are 82-83 and 29-40 kJ/mol, respectively. The ionic conduction becomes dominant in reducing atmospheres, but tends to decrease at low p(O-2). Oxygen partial pressure dependencies of Seebeck coefficient can be described by a model common for oxide phases with mixed ionic and electron-hole conductivity. Due to partial cation ordering, terbium hafnate exhibits lower ionic and hole transport as compared to TbZrO4-delta. The average thermal expansion coefficients of TbMO4-delta ( M = Zr, Hf) ceramics in air, calculated from dilatometric data, are (11.5-12.4) x 10(-6) K-1 at 600-1200 K and (18.4-20.3) x 10(-6) K-1 at 1200-1420 K.
keywords
OXYGEN-ION CONDUCTORS; FORMER SOVIET-UNION; ELECTRICAL-CONDUCTIVITY; FLUORITE; ELECTROCHEMISTRY; DIFFRACTION; PEROVSKITES; CHEMISTRY; POWDER; OXIDES
subject category
Materials Science
authors
Tsipis, EV; Shlyakhtina, AV; Shcherbakova, LG; Kolbanev, IV; Kharton, VV; Vyshatko, NP; Frade, JR
our authors
Jorge Ribeiro Frade
Retired Professor