Site occupation of doping La³⁺ cations and phase transition in Na_0.5Bi_0.5TiO₃–BaTiO₃ solid solution

Effects of La doping on the ferroelectric properties of 0.92Na_0.5Bi_0.5TiO₃–0.08BaTiO₃ (NBT–BT) solid solution have been studied both experimentally and theoretically. The experimental results show that an abnormal ferro-to-antiferroelectric phase transition is induced by La doping in NBT–BT. The first-principles calculations indicate that La³⁺ cations selectively substitute for the A site in NBT–BT as donors. Furthermore, the computed binding energy reveals that La cations is most likely to substitute for Ba²⁺ or Na⁺ to Bi³⁺ at A site as donors in NBT–BT, as supported by our Raman spectra. The ferro-to-antiferroelectric phase transition of La-doped NBT–BT is believed to originate from the lattice aberrance and redistribution of valence electrons, thus strengthening the bonding of A–O, enhancing the hybridization between the A cation d orbital and O 2p orbital, and resulting in the deflection of the polar direction of NBT–BT lattice.