Preparation and applications for new nano-sized ceramics using heterometallic-complexes as precursors

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Heterometallic oxides are one of the promising material as electrodes of fuel cells and chemical sensors. We have been proposed the thermal decomposition of heteronuclear complexes as a new method for the preparation of di- or tri-metallic oxides. We found that heterometallic oxides with relatively high specific surface area were formed at low temperature when heteronuclear hexacyano-complexes were used as precursors. The organic heteronuclear LaMn(dhbaen)(OH)(NO_3)(H_2O)_4 complex was synthesized and perovskite-type hexagonal LaMnO_3 was obtained by its thermal decomposition at 700 ℃. Particle size of the samples decomposed at 600 ℃ and 700 ℃ is ca.20 nm and 50 nm, respectively. Furthermore, homogeneous La_<1-x>Sm_xFeO_3 and YBa_2Cu_3O_7 tri-metallic oxides were prepared using same method. SmFeO_3 was applied for semiconductor-type NO_2 gas sensors and determined surface structure using XPS.The number of adsorption sites for the sample prepared by this method was larger than that by solid reaction method. On the other hand, the NASICON-type Na_3Zr_<2-(x/4)>Si_<2-x>P_<1+x>O_<12> system was prepared by sol-gel method. The sinterability was improved by an increase in x value. This seems to be caused by the liquid phase sintering. This dense electrolyte system is suitable for the application as gas sensors. The Co_2 gas sensors using highly dense x=0.667(sample B)and x=1.333(sample C)samples show a stable EMF response in dry atmosphere which is very close to the theoretical value.