Papers by Keyword: Polymerized Complex Method

Abstract: This work reports the preparation and characterization of hafnium (IV) oxide (HfO2) nanoparticles grown by derived sol-gel routes that involves the formation of an organic polymeric network. A comparison between polymerized complex (PC) and polymer precursor (PP) methods is presented. For the PC method, citric acid (CA) and ethylene glycol (EG) are used as the chelating and polymerizable reagents, respectively. In the case of PP method, poly(acrylic acid) (PAA) is used as the chelating reagent. In both cases, different precursor gels were prepared and the hafnium (IV) chloride (HfCl4) molar ratio was varied from 0.1 to 1.0 for the PC method and from 0.05 to 0.5 for the PP method. In order to obtain the nanoparticles, the precursors were heat treated at 500 and 800 °C. The thermal characterization of the precursor gels was carried out by thermogravimetric analysis (TGA) and the structural and morphological characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns of the samples obtained by both methods shows the formation of HfO2 at 500 °C with monoclinic crystalline phase. The PC method exhibited also the cubic phase. Finally, the HfO2 nanoparticles size (4 to 11 nm) was determined by TEM and XRD patterns.

Abstract: Nano-sized powders of CaCu3Ti4O12 (crystallite size of 44, 58 and 71 nm) have been synthesized by a polymerized complex method, followed by calcination the synthesized precursor at 600, 700 and 800°C in air for 8h. The CaCu3Ti4O12 powders were then characterized by XRD, FTIR and SEM. Sintering of the powders was conducted in air at 1100°C for 16h. The XRD results confirmed a typical perovskite CaCu3Ti4O12 structure in all the sintered ceramics, although the presence of a second phase of CaTiO3 was observed in the sample sintered using the powders calcined at 600°C. Microstructure of the sintered CaCu3Ti4O12 ceramics was observed by SEM and the grain size of the materials evaluated with polished using the line intercept method were found to be ~ 10-20 μm. A giant frequency-dependent dielectric constant samples (ε ~10000-60000) with weakly temperature dependence and was observed in the all the samples. The highest dielectric constant of the material was found to be ~60000 (at 140-160°C, 100 Hz) in the sample sintered using the powders calcined at 700°C. The origin of the high permittivity observed in these CaCu3Ti4O12 ceramics is attributed to the Maxwell-Wagner polarization mechanism.

Abstract: Nanosized MgAl2O4 powder was prepared following a polymerized complex oxide method. Size of the synthesized powders was 7 to 45 nm depending on the calcination temperature. Powder synthesized at lower temperature showed excellence sinterability. The relative density of the sintering body using the powder synthesized at 700°C reached up to 99.8 % at 1550°C for 3 h in air without any sintering additive.