Papers by Keyword: Cubic Phase

Abstract: Zirconium oxide was obtained via traditional precipitation from a ZrOCl₂ solution with ammonia followed by drying at 110 °C. The carbon-coated samples were synthesized by calcination of the pristine zirconia mixed with polyvinylalcohol. The obtained ZrO₂@C samples of core-shell structure as well as the reference samples of pristine zirconia were calcined at different temperatures from 500 to 1400 °C. All the materials were examined by a set of physicochemical methods (a low-temperature argon adsorption, transmission electron microscopy, X-ray diffraction analysis, photoluminescence spectroscopy). It was found that the carbon coating prevents the sintering of the oxide nanoparticles, which allows one to maintain the specific surface area, the size of the oxide core and, finally, stabilize its phase composition. Transformation of the cubic phase into monoclinic phase becomes significantly complicated. Thus, 40% of the cubic phase was detected even after calcination of the ZrO₂@C sample at 1400 °C. Moreover, the carbon-coated samples treated at elevated temperatures with subsequent removal of the carbon shell were found to possess the highest concentration of the defects related to a presence of the anion vacancies in zirconia.

Abstract: The Bi₂(Sn_0.95Mn_0.05)₂O₇ compound existing simultaneously in two polymorphic modifications, namely, orthorhombic and cubic has been synthesized for the first time by solid-phase synthesis. The magnetic, dielectric and electrical properties of the compound have been studied. Anomalies in the temperature dependences of the electrical resistance and magnetic propoties have been found. These features are explained as martensitic phase transitions.

Abstract: The theoretical method of predicating second and third order elastic constants of cubic and tetragonal material are presented by using first-principles total-energy method combined with the means of homogeneous deformation. The predicted results of SrTiO₃ provide reasonable agreement with the reported experimental data, other theoretical results and Cauchy relations. Since high order elastic constants are very difficult to be measured, the methods presented here provide a valuable guidance for experiments and the investigation of high order elastic properties for cubic and tetragonal materials.

Abstract: Hexagonal and cubic mesoporous TiO₂ materials were synthesized via a sol-gel route modified by evaporation–induced self–assembly process with different templates. XRD and TEM results confirmed that the mesoporous films were highly organized. Furthermore, the hexagonal mesoporous TiO₂ films were formed in the P123-templated films, whereas the cubic structure ones were found in the F127-templated films. Both the hexagonal and cubic mesoporous films showed photocatalytic activity in decomposing methyl orange solution under UV region, among which the cubic mesostructure presented superior potocatalytic activity because of larger surface area, more open framework and less obstructed diffusion paths of guest molecules.

Abstract: Hexagonal and cubic mesoporous TiO2 films were prepared by using triblock copolymer-templated sol-gel method via evaporation-induced self-assembly (EISA) process. The mesophase of TiO2 film was controlled by spin-speed during the spin-coating process. The hexagonal mesoporous structure was formed at a high spin-speed around 2000 rpm, whereas the cubic mesostructure was formed at a low spin-speed around 600 rpm. XRD and TEM results indicate that those mesostructures are highly organized with a pore diameter of 7 nm. The prepared cubic and hexagonal mesoporous films were tested as photocatalysts for the decomposition of 2-propanol in gas phase. Both films presented considerably higher photocatalytic activity than a nonporous TiO2 films prepared by a typical sol-gel process without addition of triblock copolymer. Notably, we found that the cubic mesoporous films showed a relatively higher photocatalytic activity than the hexagonal mesostructured film. We believe this is due to the orientation of pore channels open on the surface of mesoporous films.

Abstract: The luminescence of nanocrystalline tetragonal and cubic ZrO2 has been investigated. The tetragonal undoped ZrO2 revealed two luminescence bands, at ~2.0 eV and 2.7 eV , but only one band at ~2.7 eV was observed from cubic ZrO2. This luminescence was shown to be intrinsic. The regular zirconium-oxygen complex excited state is suggested as being responsible for intrinsic luminescence.