Influence of germanium oxide addition on the electrical properties of Li 2 OeB 2 O 3 eP 2 O 5 glasses Andrea Mogu s-Milankovi c a, * , Kristina Sklepi c a , Hrvoje Bla zanovi c a , Petr Mo sner b , Maryna Vorokhta b , Ladislav Koudelka b a RuCer Boskovic Institute, 10000 Zagreb, Croatia b Department of General and Inorganic Chemistry, University of Pardubice, Faculty of Chemical Technology, 53210 Pardubice, Czech Republic highlights graphical abstract Electrical and dielectric properties of Li 2 OeGeO 2 eB 2 O 3 eP 2 O 5 glasses were studied. GeO 2 addition causes the depolime- rization of phosphate network. Formation of Li þ conducting channels results in the el. conductivity increase. Subsequent conductivity drop is a consequence of more densely packed network. article info Article history: Received 9 April 2013 Received in revised form 15 May 2013 Accepted 16 May 2013 Available online 24 May 2013 Keywords: Lithium germano-phosphate glasses Lithium ion conductivity Electrical modulus Dielectric relaxation abstract Lithium ion transport upon the addition of germanium oxide in a series of mixed glass former lithium borophosphate glasses has been investigated. The electrical and dielectric properties of (100 x)[0.5Li 2 O e0.1B 2 O 3 e0.4P 2 O 5 ]exGeO 2 with 0e25 mol% GeO 2 glasses have been studied over a wide temperature (183e523 K) and frequency range (0.01 Hze1 MHz). The increase in dc conductivity with the addition of GeO 2 is attributed to the formation of ion conducting channels arising from the structural modification and formation of the PeOeGe linkages, resulting in an easy migration of Li þ ions along these bonds. At higher GeO 2 content glass network becomes more densely packed and ionic conductivity is slightly hindered as a consequence of the increase of bonding forces inside the network. Such a decrease in the conductivity is more reflection of the stronger cross-linkage in the glass network than that of the slight decrease in the Li þ ion concentration. The electrical modulus formalism is used to describe the dielectric relaxation. The scaling of the ac conductivity results in an excellent collapse onto common master curve whereas the electrical modulus spectra showed slight deviation indicating the distribution of relaxation times caused by the presence of various structural units in the glass network. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The need for electrolytes suitable for lithium batteries applica- tion has given rise to the investigations of numerous lithium ion based glass systems [1,2]. Glass electrolytes have certain advan- tages over their crystalline counterparts like physical isotropy, absence of grain boundaries and ease compositional variation [3]. Among lithium based glass electrolytes, lithium borophosphate glasses have been studied extensively in literature [4e6] because of their interesting structural and physical property changes upon network modifications. These systems contain two different glass formers (B and P) in the glass network responsible for an * Corresponding author. Tel.: þ385 1 4561 149; fax: þ385 1 4680 114. E-mail address: mogus@irb.hr (A. Mogus-Milankovic). Contents lists available at SciVerse ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2013.05.068 Journal of Power Sources 242 (2013) 91e98