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Dense PbTiO 3 ceramics consisting of submicrometer-sized grains were prepared using the spark-plasma-sintering (SPS) method. Hydrothermally prepared PbTiO 3 (0.1 m) was used as a starting powder. The powder was densified to տ տ98% of the theoretical X-ray density by the SPS process. The average grain size of the spark-plasma-sintered ceramics (SPS ceramics) was Շ Շ1 m, even after sintering at 900°-1100°C, because of the short sintering period (1-3 min). The measured permittivity of the SPS ceramics showed almost no frequency dependence over the range 10 1 -10 6 Hz, mainly because pores were absent from the ceramics. The coercive field of the SPS ceramics was somewhat higher than that of conventionally sintered ceramics, which could be attributed to the smallgrained microstructures of the SPS ceramics.

Dense 8 mol % yttria-stabilized zirconia (8YSZ) ceramics consisting of submicrometer-sized grains were prepared using the spark-plasma sintering (SPS) method without any additives. The starting powder (ca. 0.1 μm) was densified to ca. 99% of the theoretical X-ray density with shorter sintering time (5-10 min) while preserving a grain size in submicrometer. The measured three-point bending strength was ca. 400 MPa at room temperature for samples sintered at 1300°C for 5-10 min, which was higher than the value of conventionally sintered ceramics, ca. 250 MPa, due mainly to the small-grained microstructures of the SPS ceramics. The electrical conductivity was 0.19 S cm−1 at 1000°C in air, which is comparable to previously reported values (ca. 0.1 S cm−1) for well-sintered ceramics. Thus, the SPS method is an effective process to improve the mechanical strength of 8YSZ without degrading the electrical conductivity. © 2002 The Electrochemical Society. All rights reserved.

Test pieces with cross sections of 3•~4mm were prepared for strength testing, with the tension sides finished by a #800 diamond wind plate. The strength of the pieces was tested by the three-point bending method under the conditions of a 30mm span and a 0.5mm/min loading rate. The high-temperature test was carried out after the specimen had been kept at a specified temperature for 10min in air. Hardness was measured y a Vickers-type hard ness tester under the conditions of 93N and 30s.