PUB-2014-SAT

Stability and Thermoelectric Properties of Strontium Titanate Superlattices Incorporating Niobium Oxide Nanolayers

S.R.Kumar, MN. Hedhili, T.Tritt, and H.N. Alshareef, “Stability and Thermoelectric Properties of Strontium Titanate Superlattices Incorporating Niobium Oxide Nanolayers”
Chem. Mater., 201426 (8), pp 2726–2732
S.R.Kumar, MN. Hedhili, T.Tritt, and H.N. Alshareef
Thermoelectric Properties, Niobium Oxide Nanolayers, Strontium Titanate Superlattices
2014
A novel superlattice structure based on epitaxial nanoscale layers of NbOx and Nb-doped SrTiO3 is fabricated using a layer-by-layer approach on lattice matched LAO substrates. The absolute Seebeck coefficient and electrical conductivity of the [(NbOx)a/(Nb-doped SrTiO3)b]20 superlattices (SLs) were found to increase with decreasing layer thickness ratio (a/b ratio), reaching, at high temperatures, a power factor that is comparable to epitaxial Nb-doped SrTiO3 (STNO) films (∼0.7 W m–1 K–1). High temperature studies reveal that the SLs behave as n-type semiconductors and undergo an irreversible change at a varying crossover temperature that depends on the a/b ratio. By use of high resolution X-ray photoelectron spectroscopy and X-ray diffraction, the irreversible changes are identified to be due to a phase transformation from cubic NbO to orthorhombic Nb2O5, which limits the highest temperature of stable operation of the superlattice to 950 K.