The humidity sensing properties and mechanism of strontium-hexaferrite   ceramics
  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. 
Hui-Feng Zhang, Jian Li, Gang-Qin Shao, Zhen-Sheng Gao, Jin-Hua Liu,   H.-N. Girish
cond-mat.mtrl-sci physics.chem-ph