The effective mass is one of the main factors determining the Seebeck coefficient and electrical conductivity of thermo-electrics. In this ab-initio LDA-GGA study the effective mass is estimated from the curvature of electronic bands by one-band-approximation and is in excellent agreement with experimental data of Nb-and La-doped SrTiO 3 . It is clarified that the deformation of SrTiO 3 crystals has a significant influence on the bandgap, effective electronic DOS-mass and band-mass, but the electronic effect due to the e 2g -band flattening near the Γ-point due to Nb -doping up to 0.2 at% is the main factor for the effective mass increase. Doping of La shows a linear decrease of the effective mass; this can be explained by the different surroundings of A-and B-sites in perovskite. Substitution with other elements such as Ba on the A-site and V on the B-site in SrTiO 3 increases the effective mass as well.PACS numbers

This review article summarizes briefly some important achievements of our recent reserach on anatase and/or rutile TiO 2 thin films, fabricated by helicon RF magnetron sputtering, with good crystal quality and high density, and gives the-state-of-the-art of the knowledge on systematic interrelationship for fabrication conditions, crystal structure, composition, optical properties, and bactericidal abilities, and on the effective surface treatment to improve the optical reactivity of the obtained films.

This work aimed to prepare nanostructures of ZnO with various lasers, testing them as photocatalysts, and comparing their morphology and activity in the degradation of organic pollutants in aqueous media. ZnO nanospheres (ns-ZnO) and ZnO nanorods (ms-ZnO) were prepared via the laser ablation of a Zn metal plate in water using nanosecond- and millisecond-pulsed lasers, respectively. The obtained materials were characterized using a set of optical, structural, and surface-science techniques, such as UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Under visible-light irradiation, both nanostructures were found to be catalytically active toward the oxidation of methylene blue, which was used as a model compound. The ZnO nanorods fabricated with the millisecond laser showed better photocatalytic performance than their spherically shaped counterparts obtained by means of the nanosecond laser, which could be assigned to a larger number of defects on the ms-ZnO surface.

A homogeneous dispersion of nano iron oxide (IO) crystallites inside the hydroxyapatite (HA) particles was achieved by a co‐precipitation method. This highly stable colloidal dispersion of magnetic nano composite (HAIO) was made without the use of any surfactants. The in situ generated dispersion of the composite powders showed submicron HA particles with ~5 nm iron oxide inside. The phase analysis results showed the presence of hydroxyapatite (HA) and iron oxide with no tertiary phase. The enhancement of relative peak intensities with increased percentage of iron oxide phase in X‐ray diffraction analysis suggests the formation of iron oxide together with HA without affecting the phase purity of the latter, which is important when the biological behavior of HA is concerned. This also confirms the quantitative nature of the precipitated nanocomposites. The High Resolution Transmission Electron Microscope (HRTEM) of the composite shows elongated crystal flakes or platelike surfaces of HA crystallites having particle sizes in the range 70–100 nm. HRTEM with XRD analysis matches HAIO only with iron oxide particles of Magnetite (Fe3O4) and HA phases. The FTIR data confirm that the introduction of iron oxide did not produce any considerable change in the chemical structure of HA.

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Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band-gap of TiO 2 plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO 2 thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO 3 substrates was correlated to the lattice constants estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of 3.20 eV for bulk-anatase increases to 3.51 on SrTiO 3 . In order to interpret the optical band gap expansion for both phases, ab-initio calculations were performed using the Vienna ab-initio software. The calculations for rutile as well anatase show an almost linear increase of the band gap width with decreasing volume or increasing lattice constant a. The calculated band gap fits well with the experimental values. The conclusion from these calculations is, in order to achieve a smaller band-gap for both, rutile or anatase, the lattice constants c has to be compressed, and a has to be expanded.

In the present study, a mesoporous photocatalyst based on Au–Pd nanoparticles incorporated into g-C3N4 was prepared by a coassembly method using melamine as the carbon and nitrogen source, polyvinyl pyrrolidone as the dispersing agent, and pulse laser ablation in liquid technique for preparing gold nanoparticles and subsequent decoration with Pd nanoparticles. At the final stage, Au–Pd/g-C3N4 nano-photocatalyst was obtained via low-ramping pyrolysis in an argon atmosphere. The activity of the catalyst was related to its structure, which was characterized by high-resolution transmission electron microscopy, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and Brunauer–Emmett–Teller analysis. The results demonstrated that the Au–Pd-containing catalyst exhibited superior performance compared to its counterparts containing monometallic nanoparticles. The influence of variables such as reaction temperature, time of irradiation, amount of hydrogen peroxide, and amount of metal nanoparticles was investigated. Under optimized conditions, the Au–Pd/g-C3N4 photocatalyst showed benzene conversion of 26% at a phenol selectivity of 100%, giving no dihydroxylated byproducts. The catalyst was highly stable and recyclable, thus showing promise for the direct conversion of benzene to phenol. Time-dependent density functional theory (TD-DFT) calculations describe the activation of the oxidant by charge transferring from the metal clusters to the graphitized carbon nitride support and explain why the Au–Pd/g-C3N4 composite (rather than Au/g-C3N4) has superior efficiency in promoting the benzene-to-phenol conversion. The same DFT calculations showed that the Pd/g-C3N4 composite cannot catalyze the same processes.

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