The Adsorption of H2O on TiO2 and SnO2(110) Studied by First-Principles Calculations

First-principles calculations based on density functional theory and the pseudopotential method have been used to investigate the energetics of H$_2$O adsorption on the (110) surface of TiO$_2$ and SnO$_2$. Full relaxation of all atomic positions is performed on slab systems with periodic boundary conditions, and the cases of full and half coverage are studied. Both molecular and dissociative (H$_2$O $\rightarrow$ OH$^-$ + H$^+$) adsorption are treated, and allowance is made for relaxation of the adsorbed species to unsymmetrical configurations. It is found that for both TiO$_2$ and SnO$_2$ an unsymmetrical dissociated configuration is the most stable. The symmetrical molecularly adsorbed configuration is unstable with respect to lowering of symmetry, and is separated from the fully dissociated configuration by at most a very small energy barrier. The calculated dissociative adsorption energies for TiO$_2$ and SnO$_2$ are in reasonable agreement with the results of thermal desorption experiments. Calculated total and local electronic densities of states for dissociatively and molecularly adsorbed configurations are presented and their relation with experimental UPS spectra is discussed

Oxygen non-stoichiometry, conductivity and gas sensor response of SnO2 pellets

SnO2 pellets lose a very small amount of oxygen at high temperatures to give, for instance, the stoichiometry SnO1.9989(1) at 1200°C in air. The oxygen deficiency, δ can be preserved at ambient temperature in quenched samples. The level of conductivity, which is n-type, depends on oxygen content, 2-δ and varies by several orders of magnitude; activation energies cover the range 1.1 eV for slow-cooled, fully oxidised samples to 0.52 eV for samples quenched from 1200°C. Quenched samples can be readily and reversibly reoxidised and reduced at temperatures as low as 700°C; at lower temperatures, down to ∼350°C, oxidation and reduction is mainly confined to sample surfaces on short timescales but, nevertheless, is sufficient for the conductivity to change by 1 to 2 orders of magnitude. Quenched, oxygen-deficient samples are also moisture-sensitive whereas fully oxidised samples are not. SnO2 shows similar sensitivity to both CO2 and N2, which is attributed to loss of O2 from the sample surface

[Young woman wearing an off-the-shoulder dress and long pearl necklace, looking front, head-and-shoulders portrait]

Title devised by Library staff.On verso: From the studio of Addie Kilburn Robinson, Boston, Mass. U.S.A. DLCPhotograph attributed to F. Gercher who worked in Robinson's studio. DLCForms part of: Artistic photographs collected by Frances Benjamin Johnston in the Frances Benjamin Johnston Collection. DLCGift; Frances Benjamin Johnston; 1948. DLCPublished in: Ambassadors of progress / edited by Bronwyn A.E. Griffith ... France : Musée d'Art Américain Giverny ... 2001, p. 166

[Half-length portrait of bearded man wearing artist's smock and cap and holding a sculpting tool, facing front]

Title devised by Library staff.On verso: From the studio of Addie Kilburn Robinson, Boston, Mass., U.S.A. DLCAttributed to Fr[...]y Gercher, Addie K. Robinson's assistant.Formerly filed in P&P LOT 3222. DLCForms part of: Artistic photographs collected by Frances Benjamin Johnston in the Frances Benjamin Johnston Collection. DLCGift; Frances Benjamin Johnston; 1948 DLC.Published and misidentified as Vladimir Vasilevich Stasov in: Ambassadors of progress / edited by Bronwyn A.E. Griffith ... France : Musée d'Art Américain Giverny ... 2001, p. 166

[Man with mustache and goatee, facing left, half-length portrait]

Title devised by Library staff.On verso: From the studio of Addie Kilburn Robinson, Boston, Mass. U.S.A. DLCPhotograph attributed to F. Gercher who worked in Robinson's studio. DLCForms part of: Artistic photographs collected by Frances Benjamin Johnston in the Frances Benjamin Johnston Collection. DLCGift; Frances Benjamin Johnston; 1948. DLCPublished in: Ambassadors of progress / edited by Bronwyn A.E. Griffith ... France : Musée d'Art Américain Giverny ... 2001, p. 166