scispace - formally typeset
Search or ask a question
Author

Mattia Allieta

Bio: Mattia Allieta is an academic researcher from University of Milan. The author has contributed to research in topics: Pair distribution function & Electron paramagnetic resonance. The author has an hindex of 16, co-authored 34 publications receiving 1870 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: It is demonstrated that black TiO(2) nanoparticles obtained through a one-step reduction/crystallization process exhibit a bandgap of only 1.85 eV, which matches well with visible light absorption.
Abstract: The increasing need for new materials capable of solar fuel generation is central in the development of a green energy economy. In this contribution, we demonstrate that black TiO2 nanoparticles obtained through a one-step reduction/crystallization process exhibit a bandgap of only 1.85 eV, which matches well with visible light absorption. The electronic structure of black TiO2 nanoparticles is determined by the unique crystalline and defective core/disordered shell morphology. We introduce new insights that will be useful for the design of nanostructured photocatalysts for energy applications.

1,403 citations

Journal ArticleDOI
TL;DR: In this paper, high-resolution synchrotron x-ray powder-diffraction data showing the existence of a structural phase transition, from cubic $Pm$-3$m$ to tetragonal $I4\text{/}mcm, involving TiO{}{6}$ octahedra tilting, in analogy to the case of SrTiO${}_{3}$.
Abstract: Up to now, the crystallographic structure of the magnetoelectric perovskite EuTiO${}_{3}$ has been considered to remain cubic down to low temperature. Here we present high-resolution synchrotron x-ray powder-diffraction data showing the existence of a structural phase transition, from cubic $Pm$-3$m$ to tetragonal $I4\text{/}mcm$, involving TiO${}_{6}$ octahedra tilting, in analogy to the case of SrTiO${}_{3}$. The temperature evolution of the tilting angle and of the full width at half maximum of the (200) cubic reflection family indicate a critical temperature ${T}_{c}$ $=$ 235 K. This critical temperature is well below the recent anomaly reported by specific-heat measurement at ${T}_{A}$ \ensuremath{\sim} 282 K. By performing atomic pair distribution function analysis on diffraction data, we provide evidence of a mismatch between the local (short-range) and the average crystallographic structures in this material. Below the estimated ${T}_{c}$, the average model symmetry is fully compatible with the local environment distortion, but the former is characterized by a reduced value of the tilting angle compared to the latter. At $T$ $=$ 240 K, data show the presence of local octahedra tilting identical to the low-temperature one, while the average crystallographic structure remains cubic. On this basis, we propose that intrinsic lattice disorder is of fundamental importance in the understanding of EuTiO${}_{3}$ properties.

86 citations

Journal ArticleDOI
TL;DR: In this paper, the anodization time affected the phase composition and morphology of the growing nanotubes, which strictly influenced their photocatalytic activity, resulting in well aligned short tubes composed of anatase-rutile mixed phases.
Abstract: TiO 2 nanotube (NT) arrays of different lengths were prepared by electrochemical anodization of ca 10 cm 2 area titanium disks in NH 4 F–H 2 O–formamide solution for different times, followed by annealing at 450 °C After Pt deposition on the opposite side of the disk, the so obtained Ti-supported crystalline anodic oxides were employed as photoactive electrodes in a two compartments cell for separate H 2 and O 2 production through water photosplitting and characterized by SEM, XRD analysis and photocurrent measurements The anodization time affected the phase composition and morphology of the growing NTs, which strictly influenced their photocatalytic activity Short anodization times (40–60 min) resulted in well aligned short tubes composed of anatase-rutile mixed phases Longer anodization (>25 h) yielded thicker NT arrays covered on top by a preferentially oriented anatase layer that limited their photoactivity Photocurrent intensity measurements perfectly paralleled the water splitting activity results obtained with the different NT arrays In particular, a square-shaped fast photoresponse was recorded with ordered and fully top-open nanotubular structures On the other hand, clogged tubes not only yielded low current densities, but also showed delayed photocurrent transient signals due to the reduced mobility of the charge carriers within the preferentially oriented anatase layer NT arrays obtained under optimized conditions had a ca 80:20 anatase:rutile composition and ensured a hydrogen production rate of 83 mmol h −1 m −2 ( ie 19 NL h −1 m −2 ) in the absence of any hole scavenger or external bias

67 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented the first Pair Distribution Function (PDF) study on CGO electrolytes for solid oxide fuel cells, aiming to unveil the complex positional disorder induced by gadolinium doping and oxygen vacancies formation in these materials.
Abstract: In this work the first Pair Distribution Function (PDF) study on Ce1-xGdxO2-x/2 (CGO) electrolytes for solid oxide fuel cells is presented, aiming to unveil the complex positional disorder induced by gadolinium doping and oxygen vacancies formation in these materials. The whole range of Gd concentration xGd (0 ≤ xGd ≤ 1) of the CGO solid solutions was investigated through high resolution synchrotron radiation powder diffraction. The reciprocal space Rietveld analysis revealed in all the solid solutions the presence of positional disorder, which has been explicitly mapped into the real space. The average structural models, as obtained by the Rietveld method, fit well the experimental PDF data only for a spatial range r > ∼10 A. The same models applied at lower r values fails to reproduce the experimental curves. A clear improvement of the fit quality in the 1.5 < r < ∼6 A range was obtained for all the CGO samples applying a biphasic model encompassing both a fluorite CeO2-like and a C-type Gd2O3-like phas...

67 citations

Journal ArticleDOI
TL;DR: The so obtained hematite hierarchical morphology assures good photocurrent performance and appears to be an ideal platform for the construction of customized multilayer architecture for PEC water splitting.
Abstract: A new nanostructured α-Fe2O3 photoelectrode synthesized through plasma-enhanced chemical vapor deposition (PE-CVD) is presented. The α-Fe2O3 films consist of nanoplatelets with (001) crystallographic planes strongly oriented perpendicular to the conductive glass surface. This hematite morphology was never obtained before and is strictly linked to the method being used for its production. Structural, electronic, and photocurrent measurements are employed to disclose the nanoscale features of the photoanodes and their relationships with the generated photocurrent. α-Fe2O3 films have a hierarchical morphology consisting of nanobranches (width ∼10 nm, length ∼50 nm) that self-organize in plume-like nanoplatelets (350–700 nm in length). The amount of precursor used in the PE-CVD process mainly affects the nanoplatelets dimension, the platelets density, the roughness, and the photoelectrochemical (PEC) activity. The highest photocurrent (j = 1.39 mA/cm2 at 1.55 VRHE) is shown by the photoanodes with the best ba...

66 citations


Cited by
More filters
01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

Journal ArticleDOI
10 Mar 1970

8,159 citations

Journal ArticleDOI
TL;DR: This paper presents a meta-analyses of the chiral stationary phase transition of Na6(CO3)(SO4)2, Na2SO4, and Na2CO3 of the Na2O/Na2O 2 mixture at the stationary phase and shows clear patterns in the response of these two materials to each other.
Abstract: Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

4,353 citations

Journal ArticleDOI
Xiaoyang Pan1, Min-Quan Yang1, Xianzhi Fu1, Nan Zhang1, Yi-Jun Xu1 
TL;DR: This tutorial minireview gives a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties ofTiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO 2.
Abstract: Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theoretical calculations and experimental characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties of TiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO2. In particular, photocatalytic applications with regard to defective TiO2 are outlined. In addition, we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial minireview would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.

1,661 citations

Journal ArticleDOI
TL;DR: In this paper, a critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics).
Abstract: There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

1,489 citations