Ceramics of Ta-doping stabilized orthorhombic ZrO2 densified by spark plasma sintering and the effect of post-annealing in air

16 mol% Ta-doped ZrO powders were synthesized and densified by spark-plasma sintering (SPS) in vacuum, followed by post-SPS annealing in air, thus obtaining two ultrafine-grained ceramics consisting of Ta-doping stabilized orthorhombic ZrO. The as-SPSed ceramic is black because it is actually a suboxide essentially with reduced cations and abundant oxygen vacancies, whereas the post-annealed ceramic is white because it is an oxide without vacancies and with only partially reduced cations. Both ceramics are relatively hard and brittle, but the as-SPSed ceramic was slightly more so, attributable to crystallographic and microstructural differences. Implications of interest for the ceramics community are discussed.This work was supported by the Junta de Andalucía under Grant n° P12-FQM-1079 and from the Junta de Extremadura under Grant n° GR15078, co-financed with FEDER Funds. Financial support from the Ministerio de Economía y Competitividad (Government of Spain) and FEDER Funds under the Grants n° MAT2013–41012-P and MAT2015-71411-R is gratefully acknowledged as well