Impedance and Modulus studies of the solid electrolyte system 20CdI 2 –80[x Ag 2 O– y (0.7V 2 O 5 –0.3B 2 O 3 )], where 1  x /y  3 K.P. Padmasree a , D.K. Kanchan a, * , A.R. Kulkarni b a Department of Physics, Faculty of Science, M.S. University of Baroda, Vadodara-390002, Gujarat, India b Material Science Centre, Indian Institute of Technology, Powai, Bombay-400076, India Received 19 July 2005; received in revised form 16 December 2005; accepted 17 December 2005 Abstract In the present work, an evaluation of the transport properties of super ion conducting quaternary system 20CdI 2 – 80[x Ag 2 O– y (0.7V 2 O 5 – 0.3B 2 O 3 )], where 1  x /y  3, in steps of 0.25, to study the effect of changing the modifier to former ratio on the conduction phenomena has been undertaken. Electrical conductivity measurements were made using complex impedance method. The electrical conductivity and conductivity relaxation of the system were studied in the temperature range from 303 K to 333 K and in the frequency range from 100 Hz to 10 MHz. The highest conductivity at room temperature is obtained for the system with modifier to former ratio 1.75. Impedance and modulus analyses had indicated the temperature independent distribution of relaxation times and the non-Debye behavior in these materials. The co-operative motion due to strong coupling between the mobile Ag + ions is assumed to give rise to non-Debye type of relaxation. The silver ionic transport number (t Ag+ ) obtained by the emf technique suggested the occurrence of silver ion conduction in the CdI 2 -doped Ag 2 O–V 2 O 5 –B 2 O 3 system. D 2006 Elsevier B.V. All rights reserved. Keywords: Super ion conductors; Conductivity; Impedance; Modulus 1. Introduction Considerable interest in fast ion conducting solid electro- lytes had been seen from the number of studies reported earlier [1–4] and the high ionic conductivity of these glasses makes them interesting for many applications like solid state batteries, fuel cells, sensors, etc. These glasses have more advantages over crystalline materials because of their isotropic properties, ease of glass formation and change in properties with slight change in composition [5]. Among the fast ion conducting systems studied, AgI-doped glasses are frequently investigated because it is easy to form glassy specimens having high ionic conductivity at room temperature. The electrical characteristics of these glasses are usually measured by ac techniques to avoid the polarization effects during the dc measurements. The dc methods are considered to be inade- quate for the complete understanding of mobile ion transport properties, since frequency dispersion is inevitable in practical solid electrolytes. The ac response has made an important contribution in the study of solid electrolytes and can be analyzed in different formalisms like complex impedance Z*, complex admittance Y*, complex permittivity ( * and complex modulus M*. The advantages of using both complex imped- ance and complex modulus have been reported [6–8]. The complex electric modulus or inverse complex permittivity M*=(( *)  1 = M V + jM VV highlights the bulk effects and is complementary to impedance spectroscopy which highlights electrode effects as well. It has been reported [9] that Ag + and I  ions occupy nearest neighbor sites in the glass and that the structure of glass forming component is not affected by the addition of AgI, as confirmed by neutron diffraction [10,11] and X-ray diffraction [12,13] studies. Recently, some of the studies have been reported on silver oxysalt systems with different dopants other than AgI, which exhibit the feasibility of obtaining high silver ion conductivity at ambient temperatures [14,15]. It has been observed that conductivity increases with CdI 2 in CdI 2 – Ag 2 O–V 2 O 5 –B 2 O 3 system as reported earlier [15]. In view of this fact, in the present study, we have tried to see the effect 0167-2738/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2005.12.019 * Corresponding author. Tel.: +91 265 2795339. E-mail address: d _ k _ kanchan@yahoo.com (D.K. Kanchan). Solid State Ionics 177 (2006) 475 – 482 www.elsevier.com/locate/ssi