  The aging behavior of 3-mol%-yttria-stabilized tetragonal zirconia (3Y-TZP)
ceramics sintered in air and in reducing conditions was investigated at
140{\deg}C in water vapor. It was observed by X-ray diffraction (XRD) that
3Y-TZP samples sintered in reducing conditions exhibited significantly higher
tetragonal-to-monoclinic transformation than samples with similar density and
average grain size values but obtained by sintering in air. This fact is
explained by the increase of the oxygen vacancy concentration and by the
presence at the grain boundary region of a new aggregate phase formed because
of the exolution of Fe2+ ions observed by X-ray photoelectron spectroscopy.
