Hydrothermal Synthesis and Properties of Ceria Solid Electrolytes
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Pr substitution in Ce0 .83 Sm 0 .17 0
1 .915
is reduced, the conductivity becomes more ionic, and is
purely ionic at 2 %. However the conductivity at this lower level doping is not significantly lower. INTRODUCTION In the past several years, CeO2-based materials have been intensely investigated as catalysts, structural and electronic promoters of heterogeneous catalytic reactions and oxide ion conducting solid electrolytes in electrochemical cells [1,2]. The solid electrolyte is a key component of solid-state electrochemical devices, which are increasingly important for applications in energy conversion, chemical processing, sensing and combustion control [3-5]. Presently available oxide ion conducting solid electrolytes are mainly derived from solid solutions based on ZrO 2 (zirconia) [6,7]. Many studies have been made on other, better conductive solid electrolytes as alternatives to zirconia, e.g. Bi 20 3 [8,9] and CeO 2 [2] based materials. However, at present, the application of Bi 20 3-based materials is hindered by their limited electrolytic domain
[9].
The oxygen vacancy concentration, and concomitant oxide ion conductivity, in cerium oxide can be increased by the substitution of a lower-valent metal ion for cerium. In the past many investigations have been carried out on various aspects of ceria solid electrolytes mostly prepared by conventional ceramic methods [2,10]. Yttrium and samarium doped ceria solid electrolytes have been successfully prepared by hydrothermal method, providing low-temperature preparation and morphological control in ultrafine particles of uniform crystallite dimension [11,12]. Our systematic study of the hydrothermally prepared Cel.xSmxO 2 _x12 show maximum
ionic conductivity for the
Ce0 .83 SMo,17O 1 .915
composition [13].
Recently Mericle et al. [14]
demonstrated that by co-doping small quantities of praseodymium in Cej.xGdxO 2 .x2 solid solutions, the application region (electrolytic domain) of the electrolyte is shifted by two orders of magnitude to lower oxygen partial pressure. In this paper we present a systematic study of the structure, ionic and electronic conductivities and thermophysical properties of hydrothermally prepared samarium substituted ceria solid electrolytes doped with small amounts of Pr or Th as electron traps to extend the oxygen partial pressure application of ceria as solid electrolyte (ion transfer numbers >0.99). EXPERIMENT
Solid solutions Cel.x(Sm/Ca)xO 2-8(x=0-030) and (Ceo.8 3SmO. 17) 1.y(Tb/Pr)yO1. 9 15+8 (y=00.10) were synthesized by the hydrothermal method as previously reported for the Sm doped 149
Mat. Res. Soc. Symp. Proc. Vol. 496 01998 Materials Research Society
ceria solid electrolytes [13]. The appropriate quantities of cerium (III) nitrate hexahydrate (Ce(N0 3)36H 20, 99.9 % Aldrich), samarium (III) nitrate hexahydrate (Sm(N0 3)36H 20, 99.9 % Aldrich) or calcium nitrate hexahydrate (Ca(N0 3)2 6H 20, 99.9 % Aldrich), praseodymium (III) nitrate hexahydrate (Pr(N0 3)36H 20, 99.9 % Alfa) or terbium (III) nitrate pentahydrate (Tb(
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