Nanocomposites and nanomaterials 

Effect of Ba/Ti ratio in BaTiO3 on the crystal parameters and crystallites size 
Kovalenko O.A., Ragulya A.V.
 Department of Physics, Chemistry and Technology of Nanotextured Ceramics and Nanocomposite Materials, Institute for Problems in Materials Science of the NAS of Ukraine.
Krzhizhanovsky str., 3, Kyiv-03680, Ukraine.
E-mail: telur7@gmail.com

Barium titanate (BaTiO3) have been attracting attention of researchers due to its unique dielectric, piezoelectric, and ferroelectric properties. Under transition to the nanoscale, the dimensional effects and structural changes are manifested. These effects are described in many works [1-4]. However, since BaTiO3 is bertholides with variable composition, it’s important to detect the alterations in forms and structures of the crystal with stoichiometry changing. Therefore, in this paper, the BaTiO3 of different Ba/Ti ratios are synthesized and the dependences of crystallite sizes, tetragonality and lattice parameters on the Ba / Ti ratio are shown.
Barium titanate powder was obtained by the chemical precipitation of oxalate precursors from metal chlorides solutions with the subsequent thermal decomposition of barium titanyl oxalate to barium titanate under temperature of 750 °C and a heating rate of 10 °C / min. The obtained powder contains a mixture of tetragonal and cubic phases in the Ba/Ti ratio range of 0,96-1,026 and a mixture of low-stoichiometric phases with deviation from this range. The size of the obtained stoichiometric BaTiO3 crystallites is 27,73 nm. The TEM shows polycrystallinity and predominantly isometric round grains shape.

1.	Fang C., Zhou D. X., Gong S. P. Core-shell structure and size effect in barium titanate nanoparticle //Physica B: Condensed Matter. – 2011. –406, N 6-7. – P. 1317-1322.
2.	Uchino K., Sadanaga E., Hirose T. Dependence of the crystal structure on particle size in barium titanate //Journal of the American Ceramic Society. – 1989. – 72, N 8. – P. 1555-1558.
3.	Zhao Z. Grain-size effects on the ferroelectric behavior of dense nanocrystalline BaTiO3 ceramics //Physical Review B. – 2004. – 70, N 2. – P. 024107.
4.	Chung N. K. Enhancement of the crystallinity of barium titanate by using a uniform barium-carbonate surface coating //Journal of the Korean Physical Society. – 2017. – 70, N 9. – P. 861-865.