Feasibility of electron and hole injection in heavily doped strontium barium niobate (SBN50) Sr_(0.5)Bao.5Nb_2O_ 6 for thermoelectric applications

摘要

Undoped and heavily doped (K, Y, Zr, Mo) strontium barium niobate Sr_(0.5)Ba_(0.5)NB_2O_6 (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 s-Ad 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.