Synthesis of non-agglomerated Ba0.77Ca0.23TiO3 nanopowders by a modified polymeric precursor method

Effect of pH-induced nanopowder deagglomeration on sintering, microstructure and dielectric properties of Ba0.77Ca0.23TiO3 ceramics

“…That is, only the BCT23 phase was observed in all the XRD spectra, revealing that the initial pH value did not show any important influence on synthesizing ceramics with the stoichiometric (second phase-free) BCT23 composition envisaged. This result was expected provided that, as briefly commented in the introduction, all the powders (even those prepared from the precursor solutions with the higher pH values, and showing small amounts of a BaCO 3 phase after solution heating at 600 °C for 5 hours) resulted free of BaCO 3 traces after calcination at 700 °C and above 4 . Taking as reference, for instance, the tetragonal double (002)/(200) peak appearing in these XRD spectra just above 2q = 45°, as magnified in the Figure 5 inset, the only difference applying to all these ceramic samples is the observation of a clear trend of the double peak resolution and, thus, structure tetragonality to increase with diminishing the pH value.…”

“…Adjustment of the pH value of the resins was achieved through addition of ammonium hydroxide, followed by heating up to 120-150 °C in order to eliminate the water excess and promote the polyesterification reaction. As presented in the previous report 4 , Table 1 summarizes some of the properties of interest for the powders calcined at 600 °C for 5 hours, the data showing an evident influence of the pH value of the resin on the powder characteristics finally observed. Instead of those BaCO 3 -free powders calcined, for instance, at 700 °C for 2 hours, the present ones (Table 1) were selected as starting powders for developing this study because of their comparatively smaller average particle size, according to powders' analysis performed through field emission scanning electron microscopy, FE-SEM (FEG-VP Zeiss Supra 35 equipment).…”

“…In a preceding paper 4 , we showed that the pH values of the starting solutions effectively influenced the physical properties of BCT23 nanocrystalline powders that were synthesized by a modified polymeric precursor method. That is, increasing the pH values to alkaline conditions allowed the production of highly-reactive powders with very fine and homogeneous particles.…”

“…In practice, nevertheless, elimination of large pores from green compacts is often the common problem when dealing with sintering of nanopowders, these pores being created due to the propensity of such powders to form agglomerates during their synthesis by chemical methods 3,4 . It is well known that green compacts showing particle agglomeration normally require higher sintering temperatures than compact with well deagglomerated particles; otherwise, significantly reduced final densities of the prepared ceramics may be unfortunately obtained.…”

“…To address the above problem, adjustment of the pH value of the precursor solutions prepared via chemical synthesis-based methods has often been used as an alternative way to nearly prevent agglomerates formation and to control morphology of the powders planed to be produced [4][5][6][7][8] . In a preceding paper 4 , we showed that the pH values of the starting solutions effectively influenced the physical properties of BCT23 nanocrystalline powders that were synthesized by a modified polymeric precursor method.…”