Carrier Diffusion Model for Electrical Conductivity Response of Bi3TiNbO9 to Ambient Humidity*

The electrical properties of the metastable phase of Bi$_{3}$TiNbO$_{9}$ isomorphic to $\delta $-Bi$_{2}$O$_{3}$, in ceramic pellet form have been established. Pellets are formed by mechanochemical activation (1 to 48 h in an SPEX 8000 automatic mill), and uniaxial pressing, leading to the metastable phase in the 310 to 490 \r{ }C, as the activation time increases. Correspondingly, the stable Aurivillius phase forms in the 500 to 600 \r{ }C range. The current through pellets with $\sim $10 nm thick sputtered Pt electrodes increase by factors between 10 an 2000 in a transient from dry air to dew point of 10 \r{ }C at room temperature. The response time (10{\%} to 90{\%} of the current rise) is in the 15 to 30 s range, and it does not deteriorate under saline ambient, nor does it depend on the dry carrier gas (air, Ar, N$_{2}$, O$_{2}$, or 0.1{\%} H$_{2}$ / He). A bulk carrier diffusion model achieves a close qualitative fit to the current response to bias and humidity cycling.