Mechanically-activated synthesis and mixed conductivity of TbMO4-delta (M = Zr, Hf) ceramics
authors Tsipis, EV; Shlyakhtina, AV; Shcherbakova, LG; Kolbanev, IV; Kharton, VV; Vyshatko, NP; Frade, JR
nationality International
journal JOURNAL OF ELECTROCERAMICS
author keywords terbium zirconate; terbium hafnate; fluorite; mechanical activation; mixed conductor
keywords OXYGEN-ION CONDUCTORS; FORMER SOVIET-UNION; ELECTRICAL-CONDUCTIVITY; FLUORITE; ELECTROCHEMISTRY; DIFFRACTION; PEROVSKITES; CHEMISTRY; POWDER; OXIDES
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.
publisher KLUWER ACADEMIC PUBL
issn 1385-3449
year published 2003
volume 10
issue 3
beginning page 153
ending page 164
digital object identifier (doi) 10.1023/B:JECR.0000011214.18447.4d
web of science category Materials Science, Ceramics
subject category Materials Science
unique article identifier WOS:000187928000002
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