Paper SE+NS-MoA11
Growth, Nanostructure Formation, and Physical Properties of Single-Phase, Epitaxial, SrTiO₃-TiO₂ Nanocomposites: A Topological Insulator Approach to High-T Thermoelectrics

Monday, October 29, 2012, 5:20 pm, Room 22

Here, we present a novel approach towards creating efficient thermoelectric materials for energy conversion and thermal management under high-temperature and oxidizing environments. Several transition-metal oxide systems have recently been investigated, however most studies involve the doping of single-phase compounds to enhance electrical conductivity; while very few address decreasing thermal conductivity (in the same direction as electron transport). Thus, we present an investigation into the growth, nanostructure formation, and physical properties of epitaxial, immiscible SrTiO₃-TiO₂ nanocomposites. Sr_(1-x)Ti_(1+x)O_(3+2x) layers with 0≤x≤0.67 were grown on SrTiO₃ (001) substrates at 700°C in 1×10^-6 Torr O₂ by high-vacuum pulsed laser deposition using a KrF excimer laser (λ = 248nm) operating at 10 Hz pulse rate and 1.7 J/cm² fluence. HRXRD and XTEM results show that perovskite-structure layers grow epitaxially with a cube-on-cube orientational relationship to the substrate. The lattice parameter increases linearly while crystalline quality decreases from x=0 to x=0.67. We find a remarkably broad metastable single-phase field given the immiscible nature and crystal structure mismatch of the two alloy components. Alloying SrTiO₃ with TiO₂ leads to the formation of nanostructured compositional modulations due to the onset of spinodal decomposition, resulting in increased in electrical conductivities (due to the formation of 2D electron gas layers at the SrTiO₃-TiO₂ interfaces), decreased thermal conductivities, and enhanced thermoelectric figure of merit, large enough to compete with current state-of-the-art high-temperature thermoelectric materials.