Structural Phase Transition of (1-x)Pb(Fe_(1/2)Nb_(1/2))O_3-xPbTiO_3 Ferroelectric Ceramics

(1-x)Pb(Fe1/2Nb1/2)O3-xPbTiO3(PFN-PT) ferroelectric ceramics were prepared by the conventional ceramic processing via the wolframite precursor method.The X-ray diffraction(XRD) measurement and density measurement confirmed that the PFN-PT ceramics sintered at 1 150 ℃ for 2.5 h exhibited pure perovskite structure and high relative density.With the increase of the content of PbTiO3(PT),the crystal structure of PFN-PT changed gradually from the rhombohedral perovskite structure to the tetragonal perovskite structure,while the cell volume decreased and the tetragonality(defined as the ratio of the cell parameters c/a) of the perovskite structure increased.The PFN-PT ceramics exhibited apparent dielectric frequency dispersion.With the increase of the PT content,the temperature of dielectric maximum Tm/TC increased,the dielectric response character changed from diffused and broad dielectric peaks to relatively sharper ones,the dielectric loss decreased,and the frequency dispersion became weak.The doping of MnO2 improved dielectric property of the PFN-PT ceramics effectively,in which the values of dielectric constant maximum em and room-temperature dielectric loss tan δ were 13 254 and 0.003 63,respectively,at 100 kHz,and the values of saturation polarization Ps,coercive field Ec and piezoelectric constant d33 were 6.18 μC/cm2,1.1 kV/mm and 98pC/N,respectively,of the 0.25% MnO2-doped 0.66PFN-0.34PT ceramics.