AC conductivity and dielectric analysis of Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x)/4]O3, (x = 0, 0.02, 0.05) relaxor ferroelecric ceramics

In this paper we investigate the effect of lanthanum doping on structural, dielectric and electrical  properties  of lead magnesium niobate - lead titanate, 0.65Pb(Mg1/3Nb2/3O3)- 0.35PbTiO3 (x=0, 0.02, 0.05) ferroelectric ceramics. Dielectric and AC impedance spectroscopic measurements were carried out on pure and lanthanum doped PMN/PT ceramics over a wide temperature (30o- 450o C) and frequency interval (10 Hz-1 MHz). Pure and lanthanum doped Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x/4)]O3, (x=0, 0.02, 0.05) ceramics were prepared by solid state reaction route using columbite precursor method. X-ray diffraction revealed tetragonal (P4mm) phase for pure PMN/PT ceramics and transition to pseudo cubic phase (Pm3m) was observed with increased lanthanum doping. The dielectric response of the lanthanum modified PMN/PT ceramics was interpreted in terms of modified curie weiss law. Modulus spectroscopy revealed the deviation of dielectric behavior from ideal Debye behaviour. Activation energies calculated from dielectric relaxation and modulus spectroscopy suggested that charge transport  processes are due to oxygen ion hopping.The AC conductivity of the PMN/PT ceramics initially increased for 2 mol% of lanthanum doping followed by a subsequent decrease with further 5 mol% of  lanthanum doping. The value of the activation energies calculated from the temperature dependance of ac conductivity was in the range from 1.20-1.48 ev which is due to doubly ionized oxygen vacancies. The overall structural, electrical and dielectric behaviour of  Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x/4)]O3, (x=0, 0.02, 0.05) ceramics is correlated to the  relaxor nature induced by lanthanum doping.