Tetragonality enhancement in BaTiO₃ by mechanical activation of the starting BaCO₃ and TiO₂ powders: Characterization of the contribution of the mechanical activation and postmilling calcination phenomena

Abstract

By‐products including unwanted phase formation and/or unreacted starting materials are normally seen in the outcome of solid‐state synthesis approaches used in the literature for powder processing of advanced materials; this drawback requires critical attention and must be addressed in the new synthesis pathways in order to obtain quality powder products. A high energy mechanical milling approach was developed in this work. Addressing the drawback, the starting materials were mechanically activated by a high energy ball mill before their mixing step. It was found that highly pure barium titanate nanopowders with high tetragonality character are obtained using the approach developed here. The work also characterized tetragonality, role of the mechanical activation and postmilling thermal treatment on structure, phase formation and morphology of the obtained powder products. It was found that the mechanical activation accelerates the kinetic of formation of barium titanate and enhances the purity and tetragonality of the final products. The mechanism behind this achievement and the related reaction pattern are disclosed in this work. In order to obtain highly pure tetragonal barium titanate, a calcination temperature of 1173 K (900°C) after 30 hours mechanical activation is necessary; if these requirements are not satisfied, the final powder product contains impure phases and/or unreacted starting materials. The results also indicated that the processing conditions result in enhancement of tetragonality character of the final powder products. It seems that the method developed here can be used as a generalized methodology for obtaining the quality highly pure monosized nanocrystals of the mixed oxides for assembling in nanotechnology.

Roles of local reactivity on the solid‐state addition reaction kinetics

“…However, in many cases, other reaction steps likeoccur as well 9,10,13,14,17 . The reason for those side reactions is simply explained by insufficient supply of Ba 2+ ions throughout the host TiO 2 particles, due to too long diffusion path and impeded diffusion of Ba 2+ due to the formation of the product layer, BT.…”

“…We chose one of the most popular solid‐state addition reactions for the synthesis of polycrystalline barium titanate (BaTiO 3 , BT) from an equimolar powder mixture of BaCO 3 and TiO 2. 13‐17 …”

“…Conventional BT powder production cannot always meet such demands, 21‐24 despite tremendous efforts paid for nonconventional methods 25‐29 . Because solid‐state processes remain beneficial due to its high affordability, we have to think about the rationalization of the solid‐state processes by accounting for various possible components dominating reaction kinetics 14,15 . The same is true for many other solid‐state syntheses for more advanced modern complex oxides in a sustainable manner.…”

TiO2-Seeded Hydrothermal Growth of Spherical BaTiO3 Nanocrystals for Capacitor Energy-Storage Application

“…No peaks belonging to other identifiable impurities can be found in all the samples obtained, indicating the as-obtained BaTiO 3 samples are pure. As Figure 3b shows, the peak at about 45 • can be divided into two diffraction sub-peaks at 44.9 and 45.3 • , attributable to the (200) and (002) reflections of the tetragonal BaTiO 3 species, respectively [41]. With the increase of the R Ba/Ti value from 1.6 to 2.5, the peaks near 45 • become wider and wider, suggesting that a higher R Ba/Ti value is favorable in forming a tetragonal BaTiO 3 phase.…”

Structure and properties of nanocrystalline tetragonal BaTiO3 prepared by combustion solid state synthesis

“…However, the reactions at such high temperatures are almost impossible to control and the obtained powders often have large particle size and wide particle size distribution. The literature data indicate that solid-state synthesis from BaCO 3 and TiO 2 was used the most frequently [9][10][11]. The pure BaTiO 3 was dominantly produced by this reaction, but with irregular structure and the presence of large agglomerates.…”