20 research outputs found
Infrared response of ordered polarons in layered perovskites
We report on the infrared absorption spectra of three oxides where charged
superlattices have been recently observed in diffraction experiments. In
LaSrNiO, polaron localization is found to suppress the
low-energy conductivity through the opening of a gap and to split the
- vibrational manifold of the oxygen octahedra. Similar effects
are detected in SrLaMnO and in LaNiO, with
peculiar differences related to the type of charge ordering.Comment: File latex, 11 p. + 3 Figures, to appear on Phys. Rev. B (Rapid
Commun.), 1 Oct. 1996. The figures will be faxed upon request.
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Coexistence of localized and delocalized states in Bi-2212 Y/Ca: An investigation of the infrared and optical absorption
Synthesis and Characterization of Vanadium Substituted Potassium Tungsten Bronzes, K<sub>x</sub>V<sub>y</sub>W<sub>1-y</sub>O<sub>3</sub>
Role of ɣ-Al2O3 on the mechanical and microstructural properties of metakaolin-based geopolymer cements
The main target of this work is to investigate the influence of ɣ-Al2O3 on the properties of metakaolin-based geopolymer cements. The kaolin used as starting material for producing geopolymer cements contains approximately 28 and 64% of gibbsite and kaolinite, respectively. This kaolin was transformed to metakaolins by calcination at 500, 550, 600, 650, and 700 °C for 1 h. Gibbsite contained in kaolin was transformed to γ-Al2O3 during the calcination process. The hardener was obtained by mixing commercial sodium silicate and sodium hydroxide solution (10 M) with a mass ratio sodium silicate/sodium hydroxide equal to 1.6:1. Geopolymer cements, GMK-500, GMK-550, GMK-600, GMK-650, and GMK-700, were obtained using the prepared hardener with a mass ratio hardener/metakaolin equal to 0.87:1. It could be seen that the specific surface area of metakaolins decreases with increasing the calcination temperature of kaolin owing to the formation of the particles of γ-Al2O3. The compressive strengths 18.21/29.14/36.61/36.51 increase in the course GMK-550/GMK-600/GMK-650/GMK-700. The X-ray patterns and micrograph images of geopolymer cements, GMK-600, GMK-650, and GMK-700, indicate the presence of γ-Al2O3 in their structure. It was typically found that γ-Al2O3 remains largely unaffected during the geopolymerisation, and therefore could act as an inert filler and reinforce the structure of geopolymer cements. [Figure not available: see fulltext.]