Effect of intermediate phases on the formation of nanostructured lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoceramics by mechanical alloying

Abstract

Formation of perovskite (Bi 0.5 Na 0.5 ) 0.94 Ba 0.06 TiO 3 powders by mechanical alloying (MA) of the constituent oxides: direct creation of a small portion of BNBT from primary material, production of a significant amount of BNBT from the amorphous phase crystallization, formation of an important fraction of BNBT from pyrochlore and BNT, Polymorphic transformations of TiO 2 as a hindrance to BNBT formation, amorphization of crystalline BNBT after prolong milling. • A small portion of perovskite BNBT can be created directly from primary material. • A significant amount of BNBT was produced from the amorphous phase crystallization. • An important fraction of BNBT was created from crystalline pyrochlore and BNT. • Polymorphic transformations of TiO 2 were hindered the BNBT formation during MA. • Achievement of a fully crystalline BNBT is complicated even after prolong milling. The present study focuses on the effect of intermediate phases on the formation of perovskite (Bi 0.5 Na 0.5 ) 0.94 Ba 0.06 TiO 3 powders during mechanical alloying. Quantitative structural analyses were done by X-ray diffraction using Rietveld refinement, and microstructural studies were performed by transmission electron microscopy. The structural analyses revealed that during milling, crystalline perovskite and pyrochlore phases as well as an amorphous phase were formed, and the polymorphic transformations of TiO 2 were observed. It was found that by the milling evolution, the amorphous phase was developed considerably and after sufficient milling time, the BNBT phase prevailed over other phases, due to the crystallization of the amorphous phase as well as the pyrochlore-to-perovskite phase transformation. However, by further progression of milling, the BNBT amount was gradually decreased, owing to its transformation to the amorphous phase.