Gas-sensing properties and modeling of silver doped potassium hollandite

In this paper the gas sensing properties of Ag–K-hollandite prepared by K–Ag ion exchange are investigated. The proposed material was used as the active layer of micromachined conductometric gas sensors and tested in different environmental conditions with a number of target gases such as CO and NOx . The response to test gases was evaluated in a temperature interval from 200 to 350 ◦ C where surface phe- nomena can completely explain the sensor behavior. The proposed material was studied also by means of XPS and thermal analyses. The investigated material is a p-type semiconductor and shows a reproducible response and a complete recovery. Data obtained are discussed and a model based on surface states describing the material behavior is proposed.