Thermal depolarization studies in leukolite (polycrystalline magnesite, MgCO3)

We performed thermally stimulated depolarization current experiments on leu kolite (polycrystalline magnesite). Two bands appear in the thermograms: on e is located at 140 K (LT1 band) and another one (HT band) that reaches a m aximum around 305 K. Zn the present work, we perform the characterization o f the HT band by carrying out successive TSDC scans with electrodes of diff erent blocking degree by changing the polarization conditions and by varyin g the thickness of the specimen. The results indicate that the HT band is c haracterized by the distribution in the relaxation time and is related prob ably to the homogeneous polarization of the sample. The features can be int erpreted through an interfacial polarization mechanism like the trapping of free charges at the grain boundaries. We performed the thermal sampling sc heme and obtained a set of the constituents that build up the HT band. The fitting of a theoretical curve with normal distribution in the activation e nergy to the experimental data yielded the relaxation parameters. (C) 1999 Elsevier Science Ltd. All rights reserved.