Papers by Keyword: Polymerized Complex

Abstract: Relaxor-based ferroelectrics, 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT) with a pyrochlore-free phase, was prepared by a modified polymerized complex process. The reactive columbite (MgNb2O6) phase was synthesized by the polymerized complex method at 1050oC for 4 h with 3wt% excess MgO. Lead acetate and tetrebutyl titanate were used to synthesize pyrochlore-free PMN-PT powder via the columbite route, from 800oC to 900oC, in air for 4 h. X-ray diffraction and scanning electron microscopy were used to detect the perovskite phase evolution and the presence of the pyrochlore phase in PMN-PT. The formation of perovskite PMN-PT is a function of the time and temperature conditions of the precursor calcinations, and an optimum condition for the thermal decomposition of the precursor was determined to avoid the formation of the pyrochlore phase.

Abstract: Nanocrystalline cordierite powders were prepared by the polymerized complex method. The synthesized precursor was calcined in air at 600-1200 oC for 1h, and the calcined powders were fully characterized by TG/DTA, BET, XRD, SEM, and TEM. The XRD and selected-area electron diffraction (SAED) analysis confirmed the development of the phase composition of cordierite powders showing amorphous phase after calcination at temperature below 800oC, mixed phases of spinel and μ-cordierite phase after calcination at 800oC and 900oC, and mixed phases of spinel, μ- cordierite and α-cordierite phases after calcination at above 900oC. The BET specific surface areas of the calcined powders varied from 3 to 107 m2/g, depending on calcination temperature. The highest specific surface area of 107 m2/g was found in the powders calcined at 800oC. The average particle sizes evaluated by BET were less than 60 nm, depending on calcination temperature. The powders calcined at 800oC and 1000oC were uniaxially pressed and pressureless-sintered in air at 1250-1350oC for 2h. Densities of the sintered samples evaluated by Archimedes’s method were 87- 91 % of theoretical value. The crystal structure of all the sintered samples, determined by XRD, was mainly α-cordierite, having a small amount of spinel as second phase.