The ac conduction takes place via tunneling of overlapping large polarons in all the compositions of presently studied vanadate glasses.
In order to determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed in the frame work of various theoretical models based on classical hopping over barriers and quantum mechanical tunneling. It has been observed that mobility of charge carriers and ac conductivity in case of zinc vanadate glass system increases with increase in Bi2O3 content. Enthalpy to dissociate the cation from its original site next to a charge compensating center (Hf) and enthalpy of migration (Hm) have also been estimated. The dc conductivity (σdc), crossover frequency (ωH), and frequency exponent (s) have been estimated from the fitting of experimental data of ac conductivity with Jonscher's universal power law. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the compositions of bismuth zinc vanadate glass system. (50-x) ZnO has been studied in the frequency range 10-1 Hz to 2 MHz and in temperature range 333.16 K to 533.16 K. The ac conductivity of bismuth zinc vanadate glasses with compositions 50V2O5. Temperature and frequency dependent conductivity of bismuth zinc vanadate semiconducting glassy system Our results provide direct evidence for light-induced chemical modification of the BiVO 4 /KPi electrolyte interface. By measuring the oxygen 1s photoelectron peak intensities from the phosphate ions and liquid water as a function of time under dark and light conditions, we determine the time scales for the forward and reverse reactions. Interestingly, we find that such changes at the BiVO 4 /KPi electrolyte interface are reversible upon returning to dark conditions. The repulsive interaction between the negatively charged surface under illumination and the phosphate ions in solution causes a shift in the distribution of ions in the thin aqueous electrolyte film, which is observed as an increase in their photoelectron signals. The bismuth phosphate layer may act to passivate surface states observed in photoelectrochemical measurements. We observe that under illumination bismuth phosphate forms on the BiVO 4 surface leading to an increase of the surface negative charge. This is facilitated by the creation of a 25 to 30 nm thick electrolyte layer using the "dip-and-pull" method. In this study, we use in situ ambient pressure X-ray photoelectron spectroscopy with "tender" X-rays (4.0 keV) to investigate a polycrystalline bismuth vanadate (BiVO 4 ) electrode in contact with an aqueous potassium phosphate (KPi) solution at open circuit potential under both dark and light conditions. Light-Induced Surface Reactions at the Bismuth Vanadate/Potassium Phosphate Interface.įavaro, Marco Abdi, Fatwa F Lamers, Marlene Crumlin, Ethan J Liu, Zhi van de Krol, Roel Starr, David Eīismuth vanadate has recently drawn significant research attention as a light-absorbing photoanode due to its performance for photoelectrochemical water splitting. The capability to deposit conformal bismuth vanadates will enable a new generation of nanocomposite architectures for solar water splitting. The average photocurrents were 1.17 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode using a hole-scavenging sulfite electrolyte. BiVO4 thin films were measured for photoelectrochemical performance under AM 1.5 illumination. A selective etching process was used with vanadium-rich depositions to enable the synthesis of phase-pure BiVO4 after spinodal decomposition. The resulting films have tunable stoichiometry and may be crystallized to form the photoactive scheelite structure of BiVO4. Here, the atomic layer deposition of bismuth vanadates is reported from BiPh3, vanadium(V) oxytriisopropoxide, and water. Bismuth vanadate, BiVO4, is a promising oxide for solar water splitting where the controlled fabrication of BiVO4 layers within porous, conducting scaffolds has remained a challenge. The fabrication of porous nanocomposites is key to the advancement of energy conversion and storage devices that interface with electrolytes. Atomic Layer Deposition of Bismuth Vanadates for Solar Energy Materials.