The effect of processing conditions on varistors prepared from nanocrystalline ZnOElectronic supplementary information (ESI) available: 1) EDX associated with HRTEM of the nano-ZnO sample before and after coating with Sb, Bi and Co; 2) HRTEM and EDX associated with HRTEM of the varistor powder calcined at 300 �C after the addition of all the dopants and 3) EDX associated with FESEM of the core shell varistor sample sintered at 1050 �C. See http://www.rsc.org/suppdata/jm/b3/b306280e/