The interaction of water and carbon dioxide with nanostructured epitaxial (Ba,Sr)TiO3(001) thin film and bulk single crystal SrTiO3(001) surfaces was studied using x-ray photoemission spectroscopy (XPS), thermal desorption spectroscopy (TDS), and density functional theory (DFT). On both surfaces, XPS and TDS indicate D2O and CO2 chemisorb at room temperature with broad thermal desorption peaks (423–723 K) and a peak desorption temperature near 573 K. A comparison of thermal desorption Redhead activation energies to adsorption energies calculated using DFT indicates that defect surface sites are important for the observed strong adsorbate-surface reactivity. Numerical calculations of the competetive adsorption/desorption equilibria for H2O and CO2 on SrTiO3(001) surfaces show that for typical atmospheric concentrations of 0.038% carbon dioxide and 0.247% water vapor the surfaces are covered to a large extent with both adsorbates. The high desorption temperature indicates that these adsorbates have the potential to impact measurements of the electronic structure of BaTiO3–SrTiO3(001) surfaces exposed to air, or prepared in high vacuum deposition systems, as well as the electrical properties of thin film ATiO3-based devices.

The thermoelectric power factor of SrTiO3 is unusually high with respect to its mobility and band gap. Good thermoelectrics usually have high mobility and a narrow band gap, but such properties are not found in SrTiO3. We have determined the mechanism behind the high power factor by calculating the transport coefficients. The key to understanding the power factor is that different effective masses contribute to different transport phenomena. The discrepancy between the effective mass for the conductivity and the thermoelectric power showed that the conductivity and thermoelectric power are conveyed by electrons with different effective masses in the Brillouin zone. Light electrons were responsible for the high conductivity, whereas heavy electrons were responsible for the high thermoelectric power. The high carrier concentrations of more than 1020 cm−3 did not reduce the thermoelectric power of SrTiO3 above the classical limit. This indicates that the electrons carrying the thermoelectric power were not degenerate. This is achieved by a decrease in the Fermi energy and the contribution of the heavy electrons to the Seebeck coefficient. The strong dielectric screening also contributed to the high power factor. The Coulomb scattering by ionized impurities, which would usually reduce the carrier mobility, was effectively screened. These results clarify the mechanism behind the contribution of different types of electrons, and show that high thermoelectric power does not necessarily reduce conductivity. Our findings provide a new direction for the band engineering of thermoelectric materials.

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We examined the effect of Ca2PbO4 addition on superconductivity in a Bi-Sr-Cu-O system. We determined that Ca2PbO4 is formed in Bi-Pb-Sr-Ca-Cu-O at temperatures lower than 750°C on the basis of powder X-ray diffraction and micro-Raman scattering. A high-T c phase was synthesized by adding Ca2PbO4 to the Bi-Sr-Cu-O system which has a single CuO layer. It seems that the synthesis process of the high-T c phase is based on a reaction between the low-T c structure and Ca2+ in the liquid phase which is caused by decomposition of Ca2PbO4 at 822°C.

The electronic structure of SrTiO 3 single-crystal surfaces and their interaction with CO 2 at room temperature is studied by angle-resolved x-ray and ultraviolet photoelectron spectroscopies ͑XPS and UPS͒ and densityfunctional theory ͑DFT͒. CO 2 exposure results in spectral features in the O 1s and C 1s core levels with a binding-energy separation ⌬E ͑O 1s−C 1s͒ = 242.1Ϯ 0.2 eV. No measurable influence of CO 2 exposure on Sr and Ti core level spectra is observed. Adsorbate induced changes in XPS core levels and UPS valence-band spectra do not support SrCO 3 formation. Surface sites and bonding geometry of chemisorbed CO 2 on SrTiO 3 ͑001͒ surfaces are investigated using DFT-adsorbate-slab calculations and the calculated surface density of states compared to UPS spectra. On defect free surfaces and at lower coverages ͑⌰Ͻ0.2͒, CO 2 is predicted to strongly bond ͑E ads ϳ −1 eV͒ to both SrO and TiO 2 terminated surfaces in a monodentate structure with the C atom above a lattice oxygen. Adsorption energies, electron transfer to adsorbate, and bonding geometry are found to be strongly coverage dependent with smaller adsorption energies on TiO 2 terminated surfaces at higher coverages. These results have important implications for the identification of metal-carbonate layers on perovskite-structure metal titanate materials by photoemission spectroscopies.