Structure and Properties of Hydrogen-Charged Electrochromic Nb2O5 Ceramics
Nb2O5 ceramic pellets were prepared through sintering and hydrogen was introduced into Nb2O5 pellets through a process known as electrochemical hydrogen charging, in which Nb2O5 acted as the cathode in a 0.01 M NaOH solution. The color of Nb2O5 was found dramatically darkened after the treatment while X-ray diffraction indicated that there was no change in the crystal structure. I-V and R-T measurements showed that the resistivity was greatly decreased after hydrogen charging and the resistivity exhibited a negative-temperature-coefficient (NTC). It was proposed that hydrogen can be incorporated into Nb2O5 lattice and occupies at some interstitial site. Nb5+ of Nb2O5 is partially reduced to Nb4+ by hydrogen and the NTC-type conduction results from electron transfer between Nb5+ and Nb4+ through a hopping mechanism.
Yansheng Yin and Xin Wang
M. J. Ding et al., "Structure and Properties of Hydrogen-Charged Electrochromic Nb2O5 Ceramics", Advanced Materials Research, Vols. 79-82, pp. 1619-1622, 2009