Degradation of SrTiO3-based ceramic varistors induced by water and ac voltages

A comparison experiment was conducted in which some SrTiO3-based ceramic varistors were simply immersed in a 0.01 M NaOH solution for some periods of time while other varistors were immersed in the solution with a 50 Hz ac voltage applied between the electrodes of the varistors and a counter electrode in the solution. Though the simple immersion showed no noticeable influence on the varistors, those varistors treated with the application of the ac voltage were greatly degraded in their properties. It was proposed that the degradation resulted from the collaborated reactions of atomic hydrogen and oxygen generated in the ac voltage-induced electrolysis of water with the insulating potential barriers of the varistors. It is important to prevent water-induced degradation in SrTiO3-based ceramic varistors operating under ac voltages.