Microstructural and Property Control of Dielectrics in the La_2O_3-TiO_2 System Using Complex Colloid Particles.

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In the present study, the powder preparation of single phase compounds in the La_2O_3- TiO_2 system was examined, and then compositional and microstructural control in the multicomponent dielectrics was also investigated by using the synthesized powders from which highly densified bodies with different microstructures could be fabricated. The results obtained are as follows.1. The double oxide powders of La_2O_3・TiO_2(LT_2) and 2La_2O_3・9TiO_2(L_2T_9) were prepared from the corresponding precursor. The rapid mixing of homogeneously mixed aqueous solutions of La- and Ti-chlorides, with an excess amount of aq.NH_3, resulted in the simultaneous precipitation of both cations in a form of X-ray amorphous colloid. Examinations of the compaction and sintering behaviors of the prepared powders showed that the most densified bodies of each specimen could be readily obtained from loosely packed powder compact.2. Structural evolution in the X-ray amorphous precursor to LT_2 was examined using IR and Raman spectroscopy. Rapid coprecipitation from an aqueous solution containing unlike cationic species yielded a complex colloid which was definitely not a mixed dispersion of single-component colloids.3. Complex dielectrics consisting of mixed phases of LT_2 and La_2Sn_2O_7(LS_2) were fabricated by controlled sintering of synthesized powders. The LT_2-LS_2 dielectrics gave positive TCC(temperature coefficient of capacitance), while the dielectric constant changed linearly from 40 to 12 with increasing LS_2 content.4. Finally, the coprecipitation method established in the present study was modified and applied to produce a more complex, 1:1:4 ternary compound in the BaO-La_2O_3-TiO_2 system.