Nonlinear electrical properties of cobalt doped SnO2·Ni2O3·Nb2O5 varistors C. P. Li, J. F. Wang, W. B. Su, H. C. Chen, W. X. Wang, D. X. Zhuang and L. Xu Eur. Phys. J. AP, 16 1 (2001) 3-9 Published online: 15 October 2001 DOI: 10.1051/epjap:2001187