Effects of Ni dopant on morphology, crystal and electronic structure, electrical properties of sodium trititanate

Sodium trititanate doped with nickel in different amounts for the first time have been prepared through one-step hydrothermal synthesis. Both cation substitution and interstitial doping are realized with a formation of oxygen -deficient Na2+xTi3-yNix+yO7-delta solid solutions. The Ni-doping results in the sodium trititanate unit cell expansion. The morphology was found to be evolved with increasing dopant concentration from nanotubes to nanosheets. The specific surface area ranges from 121 to 78 m2 g-1 depending on dopant content. With nickel-doping, the bandgap narrowed from 3.45 up to 2.94eV. The conductivity of sodium trititanate increases in 3-6 fold after the nickel incorporation. A deviation from the Arrhenius temperature dependence of the conductivity is observed above 350 K indicating that mixed ionic-electronic conductors based on Ni-doped sodium trititanate are formed. This paper contributes to the advance understanding doping principles and effects for Na2Ti3O7-based materials, which are currently under consideration.