  The humidity sensitivity of n-type strontium-hexaferrite semiconductors,
X-type (Sr2Co2Fe28O46) and Z-type (Sr3Co2Fe24O41), are investigated at room
temperature. The contact and reactions between water and material surface are
demonstrated considering the formation of oxide ion vacancy, singly-ionized /
fully-ionized oxide ion vacancy, and the chemisorbed / physisorbed / condensed
water. An impedance spectra model is proposed considering the
material-electrode interface, interior material, grain boundary, absorbed water
and Warburg response. The mechanism of electronic coupled with protonic
conduction and humidity sensing mechanism are explained.
