Materials Science and Engineering B 149 (2008) 18–25 Mixed conductivity studies in silver oxide based barium vanado–tellurite glasses Meenakshi Pant, D.K. Kanchan ∗ , Poonam Sharma, Manish S. Jayswal Physics Department, Faculty of Science, M.S. University of Baroda, Vadodara 390002, Gujrat, India Received 18 August 2007; received in revised form 28 November 2007; accepted 29 November 2007 Abstract The dc conductivity and frequency dependent ac conductivity of the quaternary glass system x(BaO:1.5 Ag 2 O)–(95 - x)V 2 O 5 –5TeO 2 , are reported in the frequency range 1 Hz to 32 MHz in the temperature range from room temperature to 433 K. The dc conductivity measured in high temperature range increased with transition metal oxide content while the activation range decreased. The conductivity arises mainly from polaron hopping between V 4+ and V 5+ ions. High temperature conductivity data satisfy Mott’s small polaron hopping model. It is found that a mechanism of non-adiabatic hopping is the most appropriate conduction model for these glasses. A power law behavior σ(ω)= σ dc + Aω n (with 0 < n < 1) is well exhibited by the ac conductivity data of the glasses. The activation energy calculated from both the relaxation time and dc conductivity is found to be nearly same in both the cases. A scaling of the conductivity spectra with respect to temperature and composition is attempted and it is observed that the relaxation dynamics of charge carriers in the present glasses is independent of temperature and composition. © 2007 Elsevier B.V. All rights reserved. Keywords: Small polaron; Scaling; Ac conductivity; Non-adiabatic hopping 1. Introduction Most of the glasses are insulating in nature, but some glasses containing transition metal oxide (TMO) exhibit semi- conducting properties for higher temperature due to the existence of transition metal ion in two different valence states, for example, in V 2 O 5 containing glasses conduction occurs by the hopping of small polarons from valence state (V 4+ ) to valence state (V 5+ ). Here the unpaired 3d 1 electron induces a polarization of the surrounding lattice and the charge carrier is a small polaron. These glasses are of charge–charge-transfer or mixed valence type of semi-conducting conductors. Semi- conducting TMO glasses are important for their applications as switching and memory devices [1,2]. Vanadium tellurite glasses showed that they are semi-conducting in nature and they switch when a high electrical field is applied. They have high refractive index [3] and high IR transmittance [4,5]. In silver oxide based (BaO–V 2 O 5 –TeO 2 ) glass system, TeO 2 exhibits the best dielectric properties and BaO acts as a modifier. Ag 2 O when substituted in this barium vanado–tellurite glass sys- ∗ Corresponding author. Tel.: +91 265 2795339. E-mail address: d k kanchan@yahoo.com (D.K. Kanchan). tem, it exhibits mixed conductivity (ac as well as dc). The Ag ions act as charge carrier in this glass system and elec- tronic conductivity is exhibited due to the presence of vanadium oxides. The interaction between electron and lattice is strong enough to form small polarons and occurs by the hopping of small polarons. Dhawan et al. [6] studied non-adiabatic hop- ping in V 2 O 5 –TeO 2 glass system. In other oxide glasses like V 2 O 5 –P 2 O 5 , WO 3 –P 2 O 5 , adiabatic hopping occurs [7,8]. Not much work has been reported on dc and frequency dependent ac conductivity of V 2 O 5 –TeO 2 glasses. The purpose of the present paper is to study dc conductiv- ity and frequency dependent ac conductivity in the temperature range from room temperature to 433 K with the frequency range 1 Hz to 32 MHz and the data are analyzed using the existing theoretical models based on small polaron hopping and ionic conduction behavior. 2. Experimental procedure The glass samples of the composition [x(BaO:1.5 Ag 2 O)–(95 - x)V 2 O 5 –5TeO 2 ] were prepared by the reagent grade chemicals for x = 25, 30, 35, 40, 45 mol%. BaO was used as BaCO 3 . Required quantities of the materials were weighed and thoroughly mixed by wet grinding method. Initially 5 g 0921-5107/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2007.11.037