Highly sensitive humidity sensor based on the solid solution Zr0.2Ti0.8O2 nanofibers

Abstract The ZrxTi1-xO2 (x = 0.0 - 0.5) nanofibers were synthesized by an electrospinning process. The influences of zirconium incorporation on the structure, phase composition, lattice parameters, morphology, specific surface area, and surface states were investigated in terms of XRD, SEM, BET, and XPS tests. The humidity sensing performances were also carried out in detail. It can be concluded that the replacement of Zr at Ti-site had significant impacts with regard to the phase structure: the anatase-rutile phase transformation was inhibited by Zr4+ ion doping; Zr4+ ion was successfully incorporated into the TiO2 lattice through a substitutional mode resulting in the formation of solid solution ZrxTi1-xO2 (x = 0.1 - 0.2) with anatase structure; when the Zr4+ ion was saturated, excessive Zr4+ ion formed new phase of Ti2ZrO6 and ZrTiO4 (nominal x ≥ 0.3); the lattice parameters and the cell volume increased as Zr4+ ion incorporation. The solid solution Zr0.2Ti0.8O2 nanofibers had the highest Ti3+ abundance among the samples with x ≤ 0.2, accompanied by the highest oxygen vacancies. Moreover, the solid solution Zr0.2Ti0.8O2 nanofibers exhibited the best humidity sensing properties: excellent sensitivity as proven by four orders of magnitude change to impedance at 11% - 95% relative humidity (RH), negligible hysteresis, rapid response and recovery speed as well as superior stability, which were induced by high concentration of oxygen vacancies combined with reactive Ti3+ ions. A detailed study of the sensing mechanism was also performed in terms of complex impedance spectra.