Non-isothermal phase formation kinetics of SrBi_2Ta_2O_9-Bi_3TiTaO_9 powder derived from sol-gel precursors

摘要

Ferroelectric oxides belonging to the family of layered perovskite, the so called Aurivillius, such a SrBi_2Ta_2O_9 (SBT), were identified as promising candidates for nonvolatile ferroelectric random access memory (NvFRAM) applications due to their polarization fatigue endurance for up to 10~(12) switching cycles, good retention properties, and low leakage current densities on Pt substrates [1]. However, the application of SBT has been limited due to the high crystallization temperatures (>750 ℃) since undesirable diffusion reactions may occur at the interfacial regions, resulting in serious deterioration of whole memory devices. Recently, several attempts have been made to reduce the crystallization temperature by cation doping [2], and composition and heating condition control [3,4]. Also, Desu et al. [5,6] investigated the solid solution of SrBi_2(Ta_xNb_(1-x))_2O_9 (SBTN) and (1-x)SrBi_2Ta_2O_9-xBiTi_3Ta_3O_9 (SBT-BTT), and reported decreased crystallization temperatures and increased remanent polarization values. However, the precise reason for the reduction in the processing temperature of the solid solution systems has not been investigated. In the present work, a kinetic study has been performed to elucidate the origin of lowered crystallization temperature in the SBT-BTT solid solution system. A possible phase formation mechanism for the SBT-BTT solid solution is discussed based upon ionic bond strength and ionic dissociation energy theories.