Electrical properties of Sb and Cr-dopedPbZrO< sub> 3--PbTiO< sub> 3--PbMg< sub> 1/3 Nb< sub> 2/3 O< sub> 3 ceramics'

The pyroelectric, dielectric and DC resistive properties of Sb and Cr-doped ceramics with a base composition of Pb(Mg₁/₃Nb₂/3)_0.025 (Zr₀.₈₂₅Ti_0.175)_0.975O₃ have been studied. Sb doping has been shown to produce a linear reduction in Curie temperature (T_C=-22_z+294°C) with concentration (z) and to give an increase in pyroelectric coefficient from 250 to 310 μCm^-2 K^-1 for z increasing from 0 to 3 at.%. It also produces first a reduction and then an increase in both dielectric constant and loss, so that the 33 H_z pyroelectric figures of merit (FOM's) are as follows: F_V peaks at 3.8×10^-2m²C^-1 and F_D peaks at 1.2×10^-5 Pa^-1/2. The resistivity is increased substantially from 1.1×10¹¹ to ca 6×10¹¹ ωm with 1 at.% Sb, thereafter changing little. The behaviour has been explained in terms of Sb acting as a donor ion, reducing oxygen vacancy concentrations up to 1 at.%, with conductivity dominated by hole hopping between traps (E_a=0.59±0.05 eV) that are not changed by the Sb doping. It is concluded that additions of higher levels of Sb do not produce electron-mediated hopping conduction. The Cr additions have no effect upon T_C, but reduce dielectric constant and loss, pyroelectric coefficient and resistivity at doping levels up to 3 at.%. The FOM F_V peaks at 3.6×10^-2m²C^-1 and F_D at 1.9×10^-5 Pa^-1/2. The behaviour of the electrical resistivity as a function of dopant level is shown to produce a linear ln(σ_o) vs z^-1/3 dependence (σ^o=DC conductivity), as would be expected for hole hopping conduction between Cr³+ sites, with an E_a=0.38±10.03 eV.