Sintering constitutes an important step in the production of ceramic materials. Whatever the nature of the ceramic material considered and its field of application (nuclear ceramics, fuel cell ceramics, etc.), one of its essential characteristics is its microstructure (size and shape of grains, distribution of porosity residual). The microstructure directly affects the physico-chemical properties of the material.
We have examined the role of sintering conditions on La1.95Sr0.05Zr2O6.975 material, considered as a promising proton-conductive fuel cell electrolyte . Conventional sintering methods (UP Uniaxial Drying, IP Isostatic Pressing, HP Hot Pressing) lead to the production of low density pellets (relative densities in the range 46% to 78%) with consequent increase of crystallite size (75-235 nm). In addition, X-ray diffraction experiments and ion beam analyzes revealed a surface decomposition of the pellets obtained through conventional methods (Figure 1). The flash sintering method (SPS Spark Plasma Sintering) made it possible to obtain totally densified pellets (96%) with a crystallite size of the order of one hundred nanometers. Figure 2 shows the crystallite sizes (calculated from Williamson-Hall's law) and the densities obtained for each of the sintered pellets.
The ionic conductivity of the SPS-1500 ° C pellet is three orders of magnitude higher than the HP-1500 ° C pellet (σHP = 3.18 10-7 S.cm-1 and σSPS = 1.87 10-4 S.cm-1 at 740 ° C, relative densities of 78% and 96% respectively). The residual porosity of the material can be corrected by applying the equation proposed by Vishjager ; however, it is not sufficient to explain the difference observed. A decrease in the number of oxygen vacancies in the sintered material by conventional sintering may be responsible for this decrease in ionic conductivity .
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 D. J. Vischjager, A. A. van Zomeren, J. Schoonman, I. Kontoulis, and B. C. H. Steele, Solid State Ionics, vol. 40–41, Part 2, pp. 810–814, Aug. 1990.
 N. Q. Minh, Journal of the American Ceramic Society, vol. 76, no. 3, pp. 563–588, Mar. 1993.
Contact CEA : Suzy Surblé.