Relaxor behaviour in BaBi₄Ti₄O₁₅ ceramics fabricated using the powders obtained by mechanochemically assisted synthesis route

Abstract

Mechanochemically activated reactants were found to facilitate the synthesis of fine powders comprising 200–400 nm range crystallites of BaBi₄Ti₄O₁₅ at a significantly lower temperature (700 °C) than that of solid-state reaction route. Reactants (CaCO₃, Bi₂O₃ and TiO₂) in stoichiometric ratio were ball milled for 48 h to obtain homogeneous mixture. The evolution of the BaBi₄Ti₄O₁₅ phase was systematically followed using X-ray powder diffraction (XRD) technique. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to probe its structural and microstructural details. The electron diffraction studies established the presence of correlated octahedral rotations and associated long-range polar ordering. High-resolution TEM imaging nevertheless revealed structural inhomogeneities leading to intergrowth defects. Dense BaBi₄Ti₄O₁₅ ceramics with an average grain size of 0.9 μm were fabricated using mechanochemically assisted synthesized powders at relatively low temperature (1000 °C). The effect of grain size on the dielectric and relaxor behaviour of BaBi₄Ti₄O₁₅ ceramics was investigated. Fine-grained ceramics (average grain size ~0.9 μm) showed higher diffusion in phase transition, lower temperature of phase transition, lower Vogel-Fulcher freezing temperature and higher activation energy for the polarization reversal than those for coarse-grained ceramics (average grain size ~7 μm) fabricated via the conventional solid-state reaction route.