Copper and iron precipitates in thermochemically reduced yttria-stabilizedzirconia crystals

Thermochemical reduction (TCR) at 2173 K has been performed on nominally pu re yttria-stabilized zirconia crystals. After TCR the crystals become opaqu e owing to a very intense optical absorption band centred at 2.64 eV. Analy tical transmission electron microscopy studies have shown that both copper and iron impurity precipitates are present. Colloids with different sizes a nd shapes are inhomogeneously distributed and both large and small precipit ates are observed. Most of the large precipitates are elongated and irregul ar shaped. with an average dimension of 130 nm x 30 nm, they all contain co pper. Exclusively copper and exclusively iron contents can be Found in diff erent parts of the same precipitate, an observation that is compatible with the fact that copper and iron are inmiscible. Smaller precipitates, with a n average size of about 5 nm, are usually iron rich or copper rich.