Research Article Adv. Mat. Lett. 2013, 4(3), 185-195 ADVANCED MATERIALS Letters Adv. Mat. Lett. 2013, 4(3), 185-195 Copyright © 2013 VBRI press. www.amlett.org, www.amlett.com, DOI: 10.5185/amlett.2012.7396 Published online by the VBRI press in 2013 Equivalent circuit models and analysis of impedance spectra of solid electrolyte Na 0.25 Li 0.75 Zr 2 (PO 4 ) 3 U. Ahmadu 1* , Ŝ.Tomas 2 , S. A. Jonah 3 , A. O. Musa 4 , N. Rabiu 5 1 Department of Physics, Federal University of Technology, Minna, Nigeria 2 Faculty of Physics, Vilnius University, Lithuania 3 Centre for Energy Research and Training, Ahmadu Bello University, Zaria, Nigeria 4 Department of Physics, Bayero University, Kano, Nigeria 5 Department of Physics, Ahmadu Bello University, Zaria, Nigeria * Corresponding author. E-mail: u.ahmadu@yahoo.com Received: 25 July 2012, Revised: 15 August 2012 and Accepted: 15 August 2012 ABSTRACT Two RC model circuits are connected in series in order to analyze the electrical and dielectric behaviour of mixed alkali Na 0.25 Li 0.75 Zr 2 (PO 4 ) 3 NASICON compound. However, the data obtained could best be described by one RC circuit representing the grain boundary resistance ( ) and capacitance ( ) in the temperature and frequency range 300-600 K and 300 kHz to 1GHz, respectively. The values of the grain boundary activation energy obtained by fitting to the Arrhenius equation in a plot is ~ 0.40 eV, which is close to the bulk activation energy for electrical conduction. The maximum conductivity obtained is 0.3 S/m at 590 K. A non Debye character was observed in the dielectric permitivity in its frequency dependence. However, the temperature dependence of followed a linear behaviour at low temperatures and frequencies but decreased at higher temperatures. Complex non linear least squares fitting of impedance data using a composite circuit shows good fitting results with relative standard deviation less than 0.2 for all the free parameters which is indicative of the accuracy of data obtained. Similar good fitting results, using a generic battery model, suggest the applicability of the material in rechargeable lithium ion batteries. Copyright © 2013 VBRI press. Keywords: NZP; impedance spectroscopy; electrical conductivity; dielectric relaxation; equivalent circuit. S. A. Jonah graduated from the University of Ilorin in 1983. Professor Jonah joined the services of Ahmadu Bello University in 1985 and rose to the rank of Professor of Nuclear Physics in 2004. Professor Jonah has participated in several Conferences, Workshops, Technical Meetings and Research Coordination Meetings in Austria, Australia, Cameroon, China, Czech Republic, Ghana, Egypt, Jamaica, Morocco, South Africa, and USA. He won the International Atomic Energy Agency’s (IAEA) Research Grants in 1996, 2005, 2006 and 2008, as well as the University of Chicago, USA research grant 2010. Professor Jonah has also served as an expert of the IAEA to China Institute of Atomic Energy in 2007 and Ghana Atomic Energy Commission in 2008. He was at the Abdus Salam International Centre for Theoretical Physics, Trieste (ICTP), Italy in 2001, 2002 and 2003 and Visiting Scholar to the Nuclear Engineering Division, Argonne National Laboratory, USA in 2006 and 2010. Professor Jonah was invited to participate in the Fissile Material Working Group Meeting as an international expert at the World Nuclear Security Summit in Washington in April 2010. He has supervised several Ph. D. and M. Sc students and served as external examiner in Nigeria and Ghana. Professor Jonah has published his research findings in over 50 journal articles, mainly in high impact factor international journals and has served as peer reviewer for Applied Radiation and Isotopes and Annals of Nuclear Energy, published by Elsevier. He was the Reactor Manager and Head of Reactor Engineering Section. Ŝ. Tomas received his Ph.D. in 2009 from Vilnius University (Lithuania) under the supervision of Professor Antanas Feliksas Orliukas for work on the analysis of lithium and oxygen vacancy conducting superionic materials with impedance spectroscopy. He was a postdoctoral fellow in Universite du Maine (France) in 2010. Since 2011 T. Salkus is working at Vilnius University and in 2012 he received postdoctoral followship from Research Council of Lithuania (”Postdoctoral Fellowship Implementation in Lithuania” project). N. Rabiu born in Charanchi, Charanchi local Government, Katsina State Nigeria. He joined the services of Ahmadu Bello University, Zaria, Nigeria as Graduate Assistant in September, 1989. He had his master’s and doctorate degrees in physics in 1994 and 2005 respectively from the same University. He has held many positions in the University which include Head of Department of Physics, Assistant Dean of the faculty of Science, Faculty Examination Officer, Chairman of Academic Staff Union of Universities, Ahmadu Bello University Branch among others. Due to share hard work and commitment, he rose from the rank of Graduate Assistant to an associate Professor in 2009. He has supervised many PhD and M.Sc degrees and