Effect of hygrometry on dielectric materials

We have investigated the electrical properties of sintered disks elaborated from different type I and type II dielectric compositions by measurement of their insulation resistance versus the moisture content in air. The insulation resistance of the disks can reach values such as 1013 ohm when measured in dry air and 108 ohm when measured in a wet atmosphere. This behaviour may be due to reversible surface reactions occurring at the surface of the dense ceramics.