Electrical properties of Sb and Cr-doped PbZrO3-PbTiO3-PbMg1/3Nb2/3O3 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) (Zr0.825Ti0.175)(0.975)O-3 have been studied. Sb doping has been shown to produce a linear reduction in Curie temperature (T-C = -22z + 294 degreesC) with concentration (z) and to give an increase in pyroelectric coefficient from 250 to 310 muCm(-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 Hz pyroelectric figures of merit (FOM's) are as follows: F-v peaks at 3.8x10(-2) m(2) C-1 and F-D peaks at 1.2x10(-1) Pa-1/2. The resistivity is increased substantially from 1.1x10(11) to ca 6x10(11) Omegam 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 I 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 Fv peaks at 3.6 x 10(-2) m(2) C-1 and F-D at 1.9x10(-5) Pa-1/2. The behaviour of the electrical resistivity as a function of dopant level is shown to produce a linear ln(sigma(o)) vs z(-1/3) dependence (sigma(o)=DC conductivity), as would be expected for hole hopping conduction between Cr3+ sites, with an E-a = 0.38 +/- 0.03 ev. (C) 2002 Elsevier Science Ltd. All rights reserved.