Positive temperature coefficient of resistivity and negative differential resistivity in lead iron tunstate-lead zirconate titate

A tetragonal crystal of formula (PbFe0.67W0.33O3)(0.2)(PbZr0.53Ti0.47O3)(0.8) (PFW/PZT) was recently found to exhibit ferroelectric switching via magnetic fields of H=0.5 T at room temperature [Kumar , arXiv:0812.3875v2]. In the present study we found that this material exhibits two other unusual properties: a positive temperature coefficient of resistivity (PTCR) and negative differential resistivity. These phenomena are often considered to be unrelated and PTCR usually results from grain boundary effects, but can be bulk [D. C. Sinclair and A. R. West, J. Appl. Phys. 66, 3850 (1989)]. Within the diffusion theory of Dawber and Scott [J. Phys. Condens. Mater. 16, L515 (2004)] they are necessarily related and we fitted the present data to their diffusion-limited model.