The effects of La doping on the ferroelectric properties of 0.92Na0.5Bi0.5TiO3-0.08BaTiO3（NBT-BT） solid solution have been studied both experimentally and theoretically.The experimental results show that an abnormal ferro-toantiferroelectric 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 Ba^ 2＋or Na^＋,not Bi^3＋,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.
The synthetic fused quartz glasses with bare metal impurities have been analyzed by temperaturedependent electrical impedance spectroscopy. The complex electric impedance and the overlapping of the normalized dielectric modulus imply the single mechanism of dielectric and conduction relaxation in the fused quartz glass.Besides, the dependence of conductivity on temperature may attribute to the predominant electric relaxation to the delocalized or long range electronic hopping between the nonbridged dangling oxygen.
