Ronaldo Santos da Silva

Laser Sintering of BaTiO3 Ceramics Obtained from Nanometric Powders

We have studied the synthesis and sintering of BaTiO3 (BTO) nanometric powders produced by Pechini technique. A laser sintering procedure was applied to the BTO and its major advantage was the quickness of the processing. We have used the radiation of a CO2 laser (CW – 100 W) as the heating source. A linear rate of irradiation was applied to avoid macroscopic defects. The calcined powder at 800°C presented a single crystalline phase confirmed by the XRD and a crystallite size of 20 nm. BTO ceramics sintered at Pmax = 7.0 W/mm2 for 10 min of irradiation showed a high relative density (98 ± 1) % with an average grain size of 400 nm for a total time of sintering of 40 minutes.

Ba(Ti1 - xZrx)O3 (x = 0,05 and 0,08) Ceramics Obtained from Nanometric Powders: Ferroelectric and Dielectric Properties

We have used the Pechinis technique for synthesizing nanometric powders of Ba(Ti 1−x Zr x )O 3 (x = 0.05 and 0.08), named BTZ5 and BTZ8, respectively. The calcined powders at 750°C/2 h presented single crystalline phase and showed average particle size of about 50 nm. The BTZ sintered ceramics presented density close to 95 ± 1% and an average grain size of 1 μm. The samples showed a broader peak in the permittivity and decreasing in the maximum dielectric constant. We also observed a decrease in Curie temperature with the increased of the Zr concentration. The remnant polarization was also studied and presented dependence with the grain size.

Cation size effects-modified phase and PTCR development in Er3+ and Ca2+ co-doped BaTiO3 ceramics during sintering

Development of the positive temperature coefficient of resistivity (PTCR) in Er3+ and Ca2+ co-doped ferroelectric BaTiO3 was studied in this work, with Er3+ being used to act as a donor doping. Irrespective of all the materials showing high densities after sintering at 1200 to 1300 oC, these revealed insulator at the lowest sintering temperature, changing to semiconducting and PTCR-type materials only when the sintering temperature was further increased. Observations from X-ray diffraction help correlating this effect with phase development in this formulated (Ba,Ca,Er)TiO3 system, considering the formation of initially two separated major (Ba,Ca)TiO3- and minor (Ca,Er)TiO3-based compounds, as a consequence of cation size-induced stress energy effects. Thus, appearance and enhancement here of the semiconducting and PTCR responses towards higher sintering temperatures particularly involve the incorporation of Er3+ into the major phase, rendering finally possible the generation and percolative-like migration of electrons throughout the whole material.