Mn-doped 0.92(K_(0.5)Na_(0.5))NbO_(3)-0.08LiNbO_(3)(0.92KNN-0.08LN)lead-free piezoelectric cer-amics have been prepared by a developed sol-gel routes using Nb_(2)O_(5)as Nb source.Due to thehigh quality of gel precursor,Mn-doped 0.92KNN-0.08LN nanopowders with the mean particlesize about 20 nm were obtained at 500℃.The addition of Mn can promote the densification ofnanopowders effectively at 950℃,and also influences in a pronounced way both the crystal structure and microstructure of the materials.With the increase of the amount of Mn addition,0.92KNN-0.08LN ceramics are transformed from dominant orthorhombic to coexistence of the orthorhombic and tetragonal phases,and the grain sizes are enhanced simultaneously.Optimizedparameters,such as d_(33)=212 pC/N and k_(p)=0.46,were achieved in 0.2 Mn-doped0.92KNN-0.08LN systems,which are good candidate material for lead-free piezoelectric devices.
YUDONG HOUCHAO WANGJINGYANG RONGHAIYAN GEMANKANG ZHUHUI YAN
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.
