Study of the Dielectric Relation and the Doping Effect on Conductivity in Lithium Tantalate

Ceramics Li0.98-xTa1.004-x/5NixO3 (LTN) samples have been prepared, for x∈ { } 0;0.01;0.02;0.05;0.08;0.15;0.2 . Ac impedance measurements were carried out in the frequency range 1Hz-1MHz and from 300°C to 900°C. The influence of Ni doping on dc conductivity was depicted. Through the ac impedance, dielectric constant was deduced and two dielectric relaxations have been clearly identified at high temperature. The low frequency relaxation is attibuted to the space charges, and the high frequency one to ferroelectric dipoles. Systematic fits have been done using the Cole-Cole model. It’s appears for identified relaxations, that at the temperature close to Tc, the dispersion step ε Δ is maximum ; the relaxation time τ is thermally activated and also present an extremum at Tc. The influence of Ni doping on these relaxations, specially the relaxation of the space charges was examined.