Effect of Si content on electrophysical properties of Si-polymer composite varistors M. Ghafouri a, * , M. Parhizkar a , H. Bidadi a , S. Mohammadi Aref a , A. Olad b a University of Tabriz, Faculty of Physics, Emam St., Tabriz, Iran b University of Tabriz, Faculty of Chemistry, Tabriz, Iran highlights  A new economical composite varistor made of Si, PANI and PE has been introduced.  We could reach lower breakdown voltages by increasing Si content.  As Si content increases, nonlinearity of the varistor increase.  They have low hysteresis loop with respect to other polymer-based varistors.  Hysteresis of the varistors increases with increasing Si content. article info Article history: Received 25 September 2013 Received in revised form 11 June 2014 Accepted 22 June 2014 Available online xxx Keywords: Composite materials Hot working Electrical characterisation Electrical properties abstract Electrophysical properties of Si-polymer composite varistors, which were prepared using hot press method, have been investigated. Research on (IeV) characteristics of samples shows that by Si content exceeding 65% of the whole, samples have varistor behavior with nonlinear coefficient of about 10. Varistor breakdown voltage tends to become low in reaction to increase in Si content. Potential barriers of samples have also been investigated. The results show that increasing Si content decreases their potential barrier. These samples show a low hysteresis compared to other semiconductor-polymer composite varistors. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Rapid growth of micro and sub-micro electrical and electronical equipment has resulted in growing concern about how to protect them against surges and over voltages. An appropriate strategy to reach this goal is to hire some voltage stabilizers with proper nonlinear (IeV) characteristics, which are called “varistors”. Some metal oxide ceramics such as SnO 2 , SiC and ZnO have this nonlin- earity and are widely used as surge protectors because of their high nonlinearity near breakdown voltage. However, researchers are mainly interested in ZnO-based varistors since they are highly capable of absorbing surge energies in addition to qualified nonlinear (IeV) characteristics [1e3]. Normally, a varistor is sub- jected to a voltage lower than its breakdown voltage. When overvoltage occurs, the varistor becomes highly conductive and as voltage drops to normal case, the conductivity returns nearly back to its initial state. This behavior which is related to varistor microstructure is controlled by the electronic defects in poly- crystalline zinc oxide ceramics which are developed through the addition of different oxide additives, e.g., Bi 2 O 3 , CoO, MnO, TiO 2 , Sb 2 O 3 , etc. Typically, microstructure of ZnO varistors consists of three phases: ZnO grains, spinel phase and Bi-rich inter-granular phase [4e6]. Beside additives, varistor property is directly affected by preparation method and sintering process [6e9]. It is note- worthy that the number of grains between two electrodes and varistor thickness affect the breakdown voltage in such a way that low voltage varistors can be constructed either by decreasing the thickness of the sample or by increasing the size of ZnO grains. For ZnO varistors, it has been shown that the step voltage per each grain boundary is about 3e3.6 V/grain. This amount is not affected by amount of additives, their nature or their composition [10,11]. * Corresponding author. Tel.: þ98 914 108 8700. E-mail address: ghafouri.sar@gmail.com (M. Ghafouri). Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys http://dx.doi.org/10.1016/j.matchemphys.2014.06.066 0254-0584/© 2014 Elsevier B.V. All rights reserved. Materials Chemistry and Physics xxx (2014) 1e6 Please cite this article in press as: M. Ghafouri, et al., Effect of Si content on electrophysical properties of Si-polymer composite varistors, Materials Chemistry and Physics (2014), http://dx.doi.org/10.1016/j.matchemphys.2014.06.066