The effects of bond covalency on the chemical bonding nature and lattice stability of ferroelectric bismuth-based transition-metal oxides have been investigated systematically through comparative X-ray absorption spectroscopic studies for several Aurivillius-structured materials and their chemically reduced derivatives. According to Ti K-edge X-ray absorption near-edge structure (XANES) analysis, Bi3TaTiO9 shows a weaker strength of (TiIV-O) bonds than Bi4Ti3O12, which could be interpreted as a result of the bond competition with highly covalent (Tav-O) bonds. Also, it was found that a lithiation process gives rise to a remarkable variation of Ti local structure commonly for Bi 3TaTiO9 and Bi4Ti3O12. In contrast, there is only a slight spectral change in the Ta LIII-edge XANES spectra of Bi3TaTiO9 and SrBi2Ta 2O9 upon the chemical reduction, underscoring the higher stability of more covalent (Tav-0) bonds than (TiIV-0) bonds. Alternatively, an energy difference between the peaks corresponding to Ta 2p3/2 → Ta 5dt2g and Ta 2p3/2 → Ta 5deg transitions appears to be greater for Bi3TaTiO 9 than for SrBi2Ta2O9, indicating that the bond competition between collinear (Ta - O) and (Ti - O) bonds has a greater influence on the crystal field of TaOê octahedra than an interaction between perpendicularly aligned (Ta - O) and (Bi/Sr - O) bonds. On the basis of the present experimental findings, we are able to conclude that the highly resistive nature of the (Tav-O) bonds against the increase of electronic charge is responsible for the excellent cycle characteristics of the SrBi2Ta2O9 phase. In this regard, the incorporation of highly covalent metal ions into the octahedral sites of the Aurivillius-structured lattice is supposed to be effective in improving the lattice stability and memory performance of this ferroelectric metal oxide.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films