, Volume 4, Issue 1–2, pp 33–41 | Cite as

Studies of polarization/self-depolarization and electret-type effect in AgI

  • R. C. Agrawal
  • R. K. Gupta
  • Mohan L. Verma


A novel d.c. polarization/self-depolarization study and electret-type effect in AgI are reported. AgI pellets of varying thicknesses, placed between two blocking (graphite) electrodes, were subjected to an external d.c. potential. A state of complete polarization was attained within ∼10 min, irrespective of the sample thickness. At this state, the potential difference, developed across the sample pellet as a result of polarization/accumulation of mobile Ag+ ions at the bulk/negative electrode interface, was measured experimentally. The potential difference, obtained immediately after the removal of the external d.c. source, has been referred to as ‘instant peak potential (Vp)’. As soon as the external voltage source is switched off, a process of self-depolarization is initiated due to the chemical/self diffusion of polarized mobile Ag+ ions throughout the bulk. ‘Vp’ gives a direct information regarding the extent of mobile ion concentration (n). ‘Vp’ measurements were carried out as a function of temperature and ‘Log Vp vs 1/T’ variation was compared with the ‘Log n vs 1/T’ Arrhenius plot, reported earlier in an entirely independent study. The two variations are almost analogous. This, in turn, supported as an earlier assertion that the abrupt conductivity increase in α-AgI, after β→α-phase transition at ∼147 °C, is predominantly due to the excessive increase in ‘n’. Furthermore, it has also been revealed that the Ag+ ions play another unique role which led to the existence of ‘persistent polarization’ states in AgI. These states are identical to the ‘electret-type effects’, observed in a number of dielectric materials. The polarization state persisted for very long time in ‘thermally stimulated polarized’ sample. A detailed investigation of the persistence/retention of polarization in the thermally-stimulated-polarized sample is reported.


Polarization State Dielectric Material Peak Potential Arrhenius Plot Sample Thickness 
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Copyright information

© IfI - Institute for Ionics 1998

Authors and Affiliations

  • R. C. Agrawal
    • 1
  • R. K. Gupta
    • 1
  • Mohan L. Verma
    • 1
  1. 1.Solid State Ionics Research Laboratory, School of Studies in PhysicsPt. Ravishankar Shukla UniversityRaipurIndia

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