Non-ohmic behaviour and switching phenomena in YMnO3-based ceramic materials

Ceramic materials based on the ferroelectric compound YMnO3 have been prepared by solid state reaction of the corresponding oxides to obtain sinterable powders, which were isostatically pressed and sintered at temperatures ranging from 1350 to 1525 degrees C. The samples were characterised by X-ray diffraction, (XRD), scanning electron microscopy, (SEM), apparent density measurements, and their electrical properties were established at several temperatures. The ceramic materials showed a semiconducting behaviour when they were subject to low electrical fields. The activation energy of conductivity was calculated for a narrow range of temperatures. Applying higher electrical fields the ceramics showed non-ohmic behaviour and switching phenomena from low-to-high conductivity state with a threshold voltage which depended on the testing temperature. Values of current density as high as 80 A/cm(2) were measured in the high conductivity state. The process is reversible and the ceramics returned to low conductivity mode lowering or leaving the applied field. Analysis of the I-characteristic curves have allowed to advance a model based on the Poole-Frenkel effect. (C) 1998 Elsevier Science Limited. All rights reserved.