Bismuth titanate (Bi4Ti3O12) crystals grown from ``high‐purity'' melts are shown to have significantly lower activation fields than those reported previously when switching times are > 1 &mgr;sec. Controlled doping experiments demonstrate that the switching characteristics of Bi4Ti3O12are controlled by the crystal impurity content. Specifically, the pseudothreshold for switching is not intrinsic to the material. A model is proposed for the activation‐field control which invokes the anisotropic conductivity due to the combination of impurity content and crystal structure.