It study, employing a tight-binding Hamiltonian, the influence of chemical disorder on the electronic level spacing distribution of a silver nanoparticle containing 5083 atoms. The results indicate that in the absence of disorder the level spacing distributions are similar to those expected for systems belonging to the Gaussian Orthogonal Ensemble. Whereas, after increasing the chemical disorder, the electronic level spacing distribution and the statistics tend to the corresponding form for the Poisson Ensemble, i.e., the silver nanoparticle acquires an insulating character which is expected for strongly disordered systems. Hence, this kind of disorder produces the localization of the electronic states of the nanoparticle.

The existence of a disorder-induced metal-insulator transition (MIT) has been proved in cooled silver and copper nanoparticles by using level spacing statistics. Nanoparticles are obtained by employing molecular dynamics simulations. Results show that structural disorder is not strong enough to affect their electronic character, and it remains in the metallic regime. Whereas, electronic properties cross to the insulating regime after increasing the chemical disorder strength.

C.V.L. y H.N. agradecen a FONDECYT (CONCYTEC) por el soporte financiero a trav?s del Programa ?Centros de Excelencia?.

Alloys Fe-Al in the compositions Al25Fe75, Al50Fe50 and Al75Fe25 were synthesized by the arc furnace technique and the thermally treating 6000C. X-ray diractogram (XRD) and Mössbauer spectroscopy (MS) show the formation of the solid solution Fe(Al) rich and poor in aluminion. Tn the process of mechanical grinding to 10 hours milling maghemite γ − Fe2O3(Al) for compositions Al25Fe75 and Al50Fe50 with aluminiun atoms occupy some iron sites. In the case of the composition Al75Fe25 a single intermetallic Al13Fe4 is observed, remaining structurally invariant for all time nanostructuring.

An alternative method to determine the critical cooling rate of materials has been developed by explaining the size and cooling rate dependences of physical properties of metallic nanoparticles through the scaling theory. This method has been applied to silver and copper nanoparticles which have been obtained by molecular dynamics simulations. The results reveal that our values for critical rate are close for each studied physical quantity. Thus, by taking the average among them, we obtain 6.2(8) × 1012 K/s for silver and 8.9(5) × 1012 K/s for copper. We have also found the threshold size of nanoparticle behavior is independent of the cooling rate.

This work has been partially supported by the Brazilian agencies CNPq and CAPES. H.S.T. thanks to the Peruvian Doctoral Scholarship of CIENCIACTIVA (CONCYTEC) under Grant #218-2014-FONDECYT. C.V.L. and J.Q-M are grateful to CIENCIACTIVA (CONCYTEC) for financial support throught the Excellence Center Programs. We also acknowledge E.B. Saitovitch and CBPF for experimental facilities.

In the present work we determine the threshold of the nanoparticle behavior of copper nanoparticles by studying their structural and electronic properties. The studied nanoparticles contain from 13 to 8217 atoms and were obtained by molecular dynamics simulations using the Johnson potential for copper based on the embedded atom method. The results indicate that for small copper nanoparticles (o1000 atoms, 2.8 nm) the surface plays an important role in their physical properties. Whereas, for large nanoparticles (42000 atoms, 3.5 nm), with spherical-like external shape and large percentage of fcc-like local structure, this effect is negligible and their electronic character are similar to such expected in solid copper. Finally, it has also been shown that copper nanoparticles change their electronic character, from metallic to insulating, after increasing the strength of the chemical disor...

In this work, we study the synthesis process and structural and magnetic characterization of the ?-Al5Fe2 intermetallic alloy obtained by the arc-melting technique. Subsequently, in order to obtain homogeneous crystalline phase, all melted samples were annealed at 847?C during 2 days, and then quenched into water. The structural and micro-structural characterization of the samples were performed by X-ray diffraction and,57Fe transmission Mössbauer spectroscopy, while the morphological study was performed using scanning electron microscopy. Moreover, magnetic characterization was carried out using vibrating sample magnetometer. X-ray fluorescence was employed for elemental characterization. The results indicate that it is possible to employ the arc-melting technique to synthesize the ?-Al5Fe2 intermetallic phase with high structural quality: orthorhombic crystalline structure and Cmcm sp...

We thank DGAPA, UNAM project IN101019, and CONACYT grant A1-S-9070 of the Call of Proposals for Basic Scientific Research 2017–2018 for partial financial support. G.C.S. thanks Cienciactiva for financial support through the Doctoral Scholarship Program in Peruvian Universities (contract number 218-2014-FONDECYT). J.G.S thanks Aldo Rodriguez Guerrero for technical support. Calculations were performed in the DGCTIC-UNAM Supercomputing Center, project LANCAD-UNAM-DGTIC-051.

D. R. would like to thank the Condensed Matter Research Group of San Marcos University, where part of this work was performed. G. C. -S., H. S. T., and R. M. E. -B. are grateful to National Council of Science and Technology (CONCYTEC) from Peru for the financial support through the Doctoral Program for Peruvian Universities (Nro 218–2014-CONCYTEC). C. V. L. and D. R. are grateful to the Programa Nacional de Innovación para la Competitividad y Productividad of the Peruvian Agency Innovate Perú for financial support under contract number Nro. 457-PNICP-ECIP-2015. C. V. L. would also like to thanks the San Marcos University for partial financial support under project number B17130021.

L.M.S. thanks to the International Max Planck Research School Dynamical processes in atoms, molecules and solids and the Deutscher Akademischer Austauschdienst(DAAD) for the financial support. G.C.S. and C.V.L. are grateful to National Council of Science and Technology (CONCYTEC) from Peru for the financial support through the Doctoral Program for Peruvian Universities (Nº 218-2014-CONCYTEC) and the Peruvian Excellence Center Program, respectively. This work has also been partly supported by the German Research Foundation(DFG) within the Cluster of Excellence “Center for Advancing Electronics Dresden”. We acknowledge the Center for Information Services and High Performance Computing (ZIH) at TU Dresden for computational resources.

This work has been partially supported by the Brazilian agencies CNPq and FAPERJ. H. S. T. thanks to the Peruvian Doctoral Scholarship Program of CIENCIACTIVA (CONCYTEC) for financial support under Grand #218-2014-FONDECYT. J. Q-M and C. V. L. are grateful to CIENCIACTIVA (CONCYTEC) for partial financial support through the Excellence Center Programs. J. Q-M is also grateful to the GEMaC Laboratory, for the hospitality during the preparation of this manuscript. In addition, E. B. S. acknowledges support from FAPERJ through several grants including Emeritus Professor fellow and CNPq for BPA and corresponding grants.

L. M. S. gratefully acknowledges the International Max Planck Research School Dynamical processes in atoms, molecules and solids and the Deutscher Akademischer Austauschdienst (DAAD) for the financial support. G. C. S. and C. V. L. are grateful to the National Council of Science and Technology (CONCYTEC) from Peru for the financial support through the Doctoral Program for Peruvian Universities (No. 218-2014-FONDECYT) and the Peruvian Excellence Center Program, respectively. This work has also been partly supported by the German Research Foundation (DFG) within the Cluster of Excellence “Center for Advancing Electronics Dresden”. We acknowledge the Center for Information Services and High Performance Computing (ZIH) at TU Dresden for computational resources. Open Access funding provided by the Max Planck Society.

The Judd-Ofelt analysis is essential becauseit indicates the influence of rare earth iondoping on the host matrix in which they arefound. In the present work, the results of theoptical characterization of zinc-tellurite glassesdoped with Yb3+ are presented, varying theconcentrations of Tm3+ and Er3+ by means of UVVISabsorption spectroscopy and refractive indexmeasurements. From these results, the Judd-Ofeltparameters were obtained, which indicated astructural modification with the addition of rareearth ions in the tellurite glassy matrix, due tothe rearrangement of the glassy structure and thebreaking of Te-O bonds.

Disordered crystalline Fe50Mn25+xSn25?x alloys, with x =-1.25, 0.0, 2.5, 5.0, 7.5 (close to the full-Heusler alloys), were arc-melted in a high purity argon atmosphere and the molten pellets were individually sealed in quartz tubes also under argon atmosphere. Subsequently, they were annealed at 1173 K for 4 days, being finally quenched in a bath with cold water. Structural and magnetic properties have systematically been studied using X-ray diffraction,57Fe, and119Sn Mössbauer spectroscopies, and magnetization measurements recorded at room temperature. Rietveld refinement of the X-ray diffraction patterns of the annealed samples with x =-1.25 and 0 has revealed the presence of two hexagonal crystallographic phases: (i) a chemically disordered solid solution identified as ??(Fe/Mn)3Sn (majority fraction) and (ii) the ??Fe5Sn3 intermetallic compound (minority fraction). For samples with ...

Fe 50 Ni 50 alloy powder was prepared by milling the 1:1 stoichiometric mixture of Fe and Ni high purity elements using high energy vibrational ball-mill. Final powdered material was obtained directly after 30 h of milling process and the Rietveld analysis of the X-ray diffraction pattern of the sample reveals the presence of two Fe–Ni phases: the disordered ?–(Fe 45 Ni 55 ) alloy, with 91% of total fraction of the material (Fe–Ni solid solution plus grain boundary regions) and the chemically-ordered FeNi phase (9%), with L1 0 tetragonal structure. Average grain sizes of these Fe–Ni phases are respectively 60 nm and 20 nm. Results of extended X-ray absorption fine structure of Ni and Fe as well as 57 Fe Mössbauer spectroscopy also suggest the presence of atomically ordered FeNi phase. Mössbauer data have also shown that both Fe–Ni phases are magnetically ordered at room tempe...

H.S.T. thanks the Peruvian Doctoral Scholarship Program of CIENCIACTIVA (CONCYTEC) for financial support under Grand No. 218-2014-FONDECYT. J.Q.-M. and C.V.L. are grateful to CIENCIACTIVA (CONCYTEC) for financial support through the Excellence Centers Program. C.H.W.B. acknowledges financial support from EPSRC (Grant No.EP/J00412X/1). R.M. thanks to Institute Jean Lamour Nancy for financial support of visiting professorship. This work was supported by Ministry of Education and Science of the Russian Federation (grant 3.1992.2017/4.6). This work was also partly supported by the French PIA project “Lorraine Université d’Excellence,” reference ANR-15-IDEX-04-LUE. by the ANR-NSF Project, ANR-13-IS04-0008-01, COMAG. This work was also partly funded by the ANRT, under the CIFRE convention No. 2016/1458.