Undoped and heavily doped (K, Y, Zr, Mo) strontium barium niobate Sr0.5Ba0.5Nb2O6 (SBN50) materials have been prepared by co-precipitation. X-ray diffraction shows the formation of a single-phase product and that 10% and 12.5% of the Nb sites can be occupied by Zr and Mo, respectively. K can enter 40% of the Sr sites, while the maximum Y substitution is also around 40%. The starting stoichiometry is effective in driving the substitutions to the desired sites. X-ray Absorption Spectroscopy (XAS) at the Nb-K edge shows the presence of Nb(V) independent of doping. A pre-edge 1s-4d transition surprisingly indicates the hole injection with Y doping and the electron injection with Zr doping. Chemical reduction does not affect the stability of the structure, except for a small decrease of maximum Y solubility, while the Nb(V) oxidation state and the XAS pre-edge feature are unmodified. The oxidized samples are insulators, the reduced samples show electrical conductivity, and doping significantly enhances thermopower and electrical conductivity. The Y doped sample shows a power factor ∼30 times larger than that of the undoped sample.

Optimized 3D ZnO brush-like nanorods showing large surface area are presented as the photoanode in enhanced high-current-density DSSCs.

Nanostructuring has been proposed as an effective strategy for the reduction of the phonon contribution to the thermal conductivity, resulting in an increase in the figure of merit of thermoelectric materials. However, obtaining bulk samples presenting high relative density and nanometric grain size can be quite challenging, particularly in the case of ceramic phases. Only few examples have been reported and none in the case of Ca₃Co₄O₉. In this work, we used a sol–gel synthesis coupled with ball milling to prepare powders of Ca₃Co₄O₉ presenting a grain size as small as 4 nm. These nanopowders were then sintered at different temperature and pressures using the High-Pressure Field-Assisted Sintering Technique (HP-FAST). Relative densities up to 95 vol% where obtained while maintaining a nanometric grain size. The microstructural and electrical properties of the sintered samples have been characterized. The results show that in this oxide a reduction to the nanometric grain size produces a drastic reduction in the electrical conductivity, which cannot be compensated by the reduction in the thermal conductivity. The Seebeck effect, on the other hand, appears to be affected only marginally by the grain size and porosity.

Local environments and transport properties of heavily doped strontium barium niobates Sr0.5Ba0.5Nb2O6.