SOLID IONIC PROPERTIES OF METASTABLE ZrO_2-CeO_2-CeO_<1.5> SOLID SOLUTIONS

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In the metal-oxygen system, reduction and successive oxidation of a single phase make possible to prepare various metastable phases ; the oxidation proceeds remaining the cation distribution in the precursor of reduced phase. This principle was applied to ZrO_2 - CeO_2 system, the local atom displacements and solid ionics properties of the noble metastable phases obtained were characterizedThe precursors were prepared by reducing the t'-(Ge_<0.5>Zr_<0.5>O_2) phase at T_<de>=873K-1573K.When the precursor with T_<de>=1573K was oxidized at 873 K, a noble metastable kappa-CeZiO_4 phas was obtained in which Ce and Zr are in an ordered arrangement. The oxidation of the precursor with 1173K produced another noble metastable t'_<meta>, -(Ce_<0.5>Z_<0.5>O_2) phase in which Ce and Zr are in an disordered arrangement similar to t'-(Ce_<0.5>, Zr_<0.5>O_2). The distance between Ce-O-Ce ions decreased in the order of t'* t'_<meta> * kappa.In spite of the same composition : CeZrO_4, the electrical conductivity of the metastable t'_<meta> and kappa phases were found to be fairly larger than that of t'. The results couled be interpreted in terms of the Ce-O-Ce distance, cation distribution, and oxygen displacement. The present results imply that the electrical properties could be controlled by the preparation of metastable phase as well as doping of impurities.