Spark plasma sintering of a commercially available granulated zirconia powder—II. Microstructure after sintering and ionic conductivity G. Bernard-Granger a, * , C. Guizard a , S. Surble ´ b , G. Baldinozzi b , A. Addad c a Laboratoire de Synthe `se et Fonctionnalisation des Ce ´ramiques, UMR 3080 CNRS/Saint-Gobain, Saint-Gobain CREE, 84306 Cavaillon Cedex, France b Laboratoire Structures Proprie ´te ´s et Mode ´lisation des Solides, UMR 8580 CNRS, Ecole Centrale Paris, 92295 Chatenay-Malabry, France c Laboratoire de Structure et Proprie ´te ´s de l’Etat Solide, UMR 8008 CNRS, Universite ´ des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq Cedex, France Received 30 October 2007; accepted 17 May 2008 Available online 26 June 2008 Abstract The microstructure of TZ3Y zirconia samples sintered by spark plasma sintering was investigated using transmission electron micros- copy. The results of these observations were used to confirm the mechanisms involved in the control of densification. For the second time, the ionic conductivity of some samples obtained by SPS was investigated as a function of temperature. The results were compared with the best results found in the literature and discussed. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Ceramics; Transmission electron microscopy; Electrical resistivity/conductivity 1. Introduction Spark plasma sintering (SPS) of a commercially avail- able TZ3Y granulated zirconia powder (Tosoh Europe BV, Amsterdam, The Netherlands) was investigated and reported in a previous companion paper [1]. By building the ‘‘grain size vs. relative density” trajectory, it was shown that three types of microstructure, depending on the exper- imental parameters other than the heating rate (fixed to 50 °C min 1 ) and the applied macroscopic compaction pressure (fixed to 100 MPa), were achievable [1]. Porous materials (opened porosity, relative density between 61% and 90%) with nanometer grain size (80 nm) were obtained when the temperature was <1050 °C whatever the soak time, or when the temperature was 1050 °C and the soak time limited to 15 min. Dense materials (closed porosity, relative density between 90% and 98%) with a nanometer grain size (80 nm) were obtained at tempera- tures ranging from 1125 to 1200 °C whatever the soak time, or when the temperature was 1050 °C and the soak time >60 min. Lastly, a fully dense material with a submicron grain size (160 nm) was achieved for a temperature of 1200 °C and 3 h of soak. For the first time, the mechanisms controlling the densi- fication of granulated stabilized zirconia raw powder dur- ing SPS experiments were also determined [1]. When the effective compaction stress and/or the temperature were low, a pure diffusion mechanism (bulk?) was probably responsible for the densification. At intermediate effective compaction stresses and/or medium temperatures, a stress exponent of two, associated with an apparent activation energy of 450 kJ mol 1 , were determined using a densifica- tion law derived from an analogy with high-temperature creep models. In that case, it was proposed that densifica- tion proceeded by grain boundary (GB) sliding accommo- dated by an in-series (interface-reaction/lattice diffusion of 1359-6454/$34.00 Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2008.05.031 * Corresponding author. Tel.: +33 4 32 50 09 21; fax: +33 4 32 50 09 21. E-mail address: guillaume.bernard-granger@saint-gobain.com (G. Bernard-Granger). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 56 (2008) 4658–4672