Preparation and Sintering of Perovskite-Type Compound Powders by the Hydrazine Method

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Submicron powders consisting of various kinds of perovskite-type compounds (PbZrO_3, LaCrO_3, LaCr_<0.85>Mg_<0.15-x>Co_xO_3 (x=0,0.05,0.10) have been prepared by the hydrazine method. Characterization of powders have been performed using transmission electron microscopy, differential thermal analysis, thermal gravimetry, X-ray diffraction analysis, and BET method. LaCr_<0.85>Mg_<0.15-x>Co_xO_3 powders have been sintered. Electrical and thermal properties of the sintered ceramics have been evaluated.1) PbZrO_3 Metastable ZrO_2 solid solutions containing up to 50 mol% PbO are formed at low temperatures from as-prepared amorphous materials ; the tetragonal phase up to 30 mol% PbO and the cubic phase between 30 and 50 mol% PbO.The compound PbZrO_3 is formed at 615ﾟ to 690ﾟC by transformation of c-ZrO_2 solid solution.2) LaCrO<@D23@>D2 Metastable LaCrO<@D24@>D2 crystallizes at (]SYgtoreq[)530ﾟC from as-prepared materials. The compound LaCrO<@D23@>D2 consisting of submicron powders (0.2mum) … More is formed at 840ﾟC by transformation of LaCrO<@D24@>D2.3) LaCr<@D20.85@>D2Mg<@D20.15-x@>D2Co<@D2x@>D2O<@D23@>D2 (x=0,0.05,0.10) As the same result as LaCrO<@D23@>D2, metastable LaCrO<@D24@>D2 solid solutions crystallize at low temperatures ((]SYapprxeq[)480ﾟC) from as-prepared amorphous materials. LaCrO<@D24@>D2 solid solutions transform at(]SYapprxeq[)780ﾟC into the compounds LaCr<@D20.85@>D2Mg<@D20.15-x@>D2Co<@D2x@>D2O<@D23@>D2 (x=0,0.05,0.10) consisting of submicron powders ((]SYapprxeq[)0.12mum). After being calcined at 1000ﾟC for 1h, the powders compacted into pellets at 343 MPa have been sintered at 1600ﾟC for 2h. Well-densified compacts ((]SYapprxeq[) 95% of theoretical) can be obtained, although these compounds show poor sinterability. The LaCr<@D20.85@>D2Mg<@D20.15-x@>D2Co<@D2x@>D2O<@D23@>D2 ceramics obtained show high electric conductivity of (]SYapprxeq[)8.8S・cm<@D1-1@>D1 at 1000ﾟC ; this value is about ten times higher than that of LaCrO<@D23@>D2 ceramics reported. Thermal expansion coefficients of ceramics alpha are (]SYapprxeq[)11.3-12.0x10<@D1-6@>D1K<@D1-1@>D1 in the temperature range between room temperature and 1000ﾟC ; the values are the same as c-ZrO<@D22@>D2. These results reveal that the LaCr<@D20.85@>D2Mg<@D20.15-x@>D2Co<@D2x@>D2O<@D23@>D2 ceramics are suitable candidates for electrodes in solid oxide fuel cell (SOFC) composed of c-ZrO<@D22@>D2 as a solid electroloyte. Less