Alessandro Mancini

CH3NH3SnxPb1–xBr3 Hybrid Perovskite Solid Solution: Synthesis, Structure, and Optical Properties

We report the synthesis and characterization of a MASnxPb1-xBr3 (MA = methylammonium; nominal x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) solid solution. The original synthetic method developed allowed one to obtain single-phase materials with homogeneous Sn/Pb distribution. All of the samples prepared are cubic, and the unit cell linearly decreases with increasing x value. The optical response indicates a linear trend (Vegards law) of the band gap with increasing Sn content from 2.20 eV (x = 0) to 1.33 eV (x = 1), thus extending light absorption into the near-IR.

Correlation between Deposition Parameters and Hydrogen Production in CuO Nanostructured Thin Films.

In this article, we report a systematic investigation of the role of (i) substrate temperature, (ii) oxygen partial pressure, and (iii) radio frequency (rf) power on the crystal structure and morphology of CuO nanostructured thin films prepared by means of rf-magnetron sputtering starting from a Cu metal target. On selected films, photocatalytic tests have been carried out in order to correlate the structural and morphological properties of the thin films prepared under different conditions with the photocatalytic properties and to find out the key parameters to optimize the CuO nanostructured films. All of the synthesized films were single-phase CuO nanorods of variable diameter between 80 and 200 nm. Better-aligned rods were obtained at relatively low substrate temperatures and from low to intermediate oxygen partial pressures, resulting in more efficient photocatalytic activities. Our investigation suggests a relevant role of the crystallographic orientation of the CuO tenorite film on the photocatalytic activity, as demonstrated by the significant improvement in H2 evolution for highly oriented films.

Interstitial oxide ion migration in scheelite-type electrolytes: a combined neutron diffraction and computational study

W-doped LnNbO4+d compounds (Ln = La, Nd) have been recently proposed as novel interstitial-based oxide ion conductors. In this study, a powerful combination of neutron diffraction, ab initio calculations and classical molecular dynamic simulations is used in a complementary way to investigate the high temperature behavior of this system, identify possible oxygen interstitial positions and investigate the mechanism of oxygen diffusion at a high temperature. The results indicate that both systems (LaNb0.84W0.16O4.08; NdNb0.84W0.16O4.08) undergo a phase transition from a monoclinic to a tetragonal phase as a function of temperature. In the scheelite phase more than one interstitial site is potentially accessible based on the calculated energy differences. The accessibility of such interstitial positions poses the basis for an efficient oxygen diffusion migration that is predicted to be roughly isotropic and based on a knock-on mechanism.

Correlation between the local scale structure and the electrochemical properties in lithium orthosilicate cathode materials

Lithium metal orthosilicates with general formula Li2MSiO4 (M = Mn, Fe and Co) are among the most attractive new materials as potential high-specific-energy cathodes for lithium batteries. All the members of this family present a rich polymorphism with at least three clearly identified crystal structures of each Li2MSiO4 compound. Several theoretical investigations have highlighted that the energy stability of the different polymorphs is very close to each other irrespective of their average crystal structures. At the same time, the calculated and experimental electrochemical performances are again very similar among different polymorphs. By means of neutron total scattering investigation of different polymorphs (monoclinic and orthorhombic) of Li2FeSiO4 and Li2MnSiO4 orthosilicates coupled to Pair Distribution Function (PDF) analysis we showed that, at the local scale, all the polymorphs have the same structure (in particular the structure of the monoclinic polymorph) irrespective of the average structure they possess. This experimental evidence of a strong similarity at the local scale can be correlated with the observed electrochemical similarity (such as the lithium extraction voltages) among the different orthosilicate polymorphs, thus providing an approach to elucidate the relevance of local versus long-range structure.