Undoped and Ni-doped cobalt oxide (Ni=4%) powders were prepared by hydrothermal synthesis and subsequently examined. The powders obtained were subjected to thermal annealing at temperatures ranging between 600 degrees C and 1000 degrees C. The experimental results indicate that the annealing affects the structural properties with the phase change Co3O4 to CoO. X-Ray diffraction (XRD) analysis reveals the presence of pure spinel phase up to 800 degrees C in powders obtained with and without the addition of nickel. From 900 degrees C, the CoO phase was observed. Rietveld refinement was conducted with main GOF values between 1.09 and 1.26 and also x(2) values between 1.28 and 1.57, indicating a good correspondence between the simulated and the experimental pattern. In addition, SEM measurements evidenced that particle size increased with temperature; however, samples doped with Ni exhibited a slightly smaller size compared to pure samples. The synthesized powders showed shifted and broad bands Raman, with increasing temperature, mainly for doped samples. These changes in the position of Raman vibrational modes are related to defects and distortions in the crystal lattice of the material as a result of the increase in temperature and the addition of Ni. Furthermore, such changes may also indicate loss of crystallinity in the material, or the beginning of the phase change.

Agglomerates of $$\text{Co}_{3}\text{O}_{4}$$ were obtained using the sol–gel method for the synthesis with subsequent calcination of the samples up to 550 °C. Through X-rays it was observed that the samples presented the pure spinel phase with a crystallite size between 33.73 and 41.45 nm. In the thermogravimetric measurement from 262 °C high structural stability is presented with phase change at 917 °C. As the temperature increases, the particles increase in size, observing agglomerated nanometer particles that increase with temperature (3.5–3.8 μm). The 683 cm $$^{-1}$$ Raman mode for 550 °C clearly presents an shifted compared to the other samples. The band gap for the samples under study varied with the temperature change of 1.77–1.81 eV. The FWHM decreases at a higher temperature, this confirms the larger crystallite size and the higher degree of sintering.

gglomerates of Co_3O_4 were obtained using the sol–gel method for the synthesis with subsequent calcination of the samples up to 550 °C. Through X-rays it was observed that the samples presented the pure spinel phase with a crystallite size between 33.73 and 41.45 nm. In the thermogravimetric measurement from 262 °C high structural stability is presented with phase change at 917 °C. As the temperature increases, the particles increase in size, observing agglomerated nanometer particles that increase with temperature (3.5–3.8 μm). The 683 cm ^-1 Raman mode for 550 °C clearly presents an shifted compared to the other samples. The band gap for the samples under study varied with the temperature change of 1.77–1.81 eV. The FWHM decreases at a higher temperature, this confirms the larger crystallite size and the higher degree of sintering.

Agglomerates of Co3O4\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Co}_{3}\text{O}_{4}$$\end{document} were obtained using the sol–gel method for the synthesis with subsequent calcination of the samples up to 550 °C. Through X-rays it was observed that the samples presented the pure spinel phase with a crystallite size between 33.73 and 41.45 nm. In the thermogravimetric measurement from 262 °C high structural stability is presented with phase change at 917 °C. As the temperature increases, the particles increase in size, observing agglomerated nanometer particles that increase with temperature (3.5–3.8 μm). The 683 cm-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{-1}$$\end{document} Raman mode for 550 °C clearly presents an shifted compared to the other samples. The band gap for the samples under study varied with the temperature change of 1.77–1.81 eV. The FWHM decreases at a higher temperature, this confirms the larger crystallite size and the higher degree of sintering.

Oxide ceramics with the nominal composition Ca2-xSrxCo2O5 were prepared using the sol-gel method. The transport properties were evaluated using Seebeck coefficient S(T) and electrical resistivity ρ(T) measurements. ST exhibited positive values, suggesting a p-type material, which increased with the Sr content. The electrical resistivity revealed a metallic behavior. ρ(T) decreased with the Sr content, reaching minimum values close to 18mΩcm. From S(T) and ρ(T) data, the thermoelectric (TE) power factor was calculated, which reached maximum values close to 4μWK-2cm-1. Thus, these ceramics can be considered to be promising materials for use in low-temperature thermoelectric applications

With the objective of development of optoelectronic devices, nowadays the research in this field is centred around the study of photoluminescence emission of rare earth elements present in the lattice of different oxides. Therefore, in this study we prepared samples of molybdenum trioxide doped with neodymium and erbium at concentrations of 1.0% and 2.0%, using solid state reaction technique from powders of MoO3, Nd2O3 and Er2O3. These powders were analysed by X-ray diffraction which determined the presence of phase alpha-MoO3. The morphology of the powders was examined using scanning electron microscopy, which showed that the doped samples have regular and well-defined microplates. The absorption UV-spectra revealed that the optical band gap changed slightly (3.2-3.4 eV) with the Er, Nd and Er-Nd concentrations. The photoluminescence shows emission bands at different wavelengths of the visible spectra as a function of the Er, Nd, and Er-Nd doped. The bands were centred at 748 nm and 808 nm transitions of the Nd3+ ions respectively. In this region and with excitation wavelength of 350 nm, strong emission lines were not observed for Er. Raman spectroscopy showed typical modes of vibration of alpha-MoO3. Major changes have been noted in the case of samples doped with Er at peaks located between 350 cm(-1) and 580 cm(-1).

We studied the crystallinity, morphology, and surface composition of Nd-doped molybdenum oxide films grown on glass slides through spray pyrolysis. After fabrication, the films were subjected to thermal treatment in oxygen for periods ranging from 2 to 20 hours. The films were structurally characterized through X-ray diffraction (XRD), their bulk chemical composition was determined using Energy-Dispersive X-ray analysis (EDX), and their surface composition was determined using X-ray Photoelectron Spectroscopy (XPS). The XRD results show that the films obtained from different dissolution volumes and at substrate temperature of 300 degrees C exhibit the characteristics of the oxygen-deficient molybdenum trioxide Mo9O26 phase. The films subjected to different thermal treatments exhibit a mixture of Mo9O26 and Mo17O47 phases. EDX study shows the energy belonging to the L line of Nd. Finally, films doped with Nd and subjected to a thermal treatment of 20h were analyzed through XPS, showing the binding energies at the crystalline lattice correspond to Nd (MoO4)(3) and Nd2Mo2O7.

This paper exposes and details the most relevant methods for the solution of the Resource Constrained Project Scheduling Problem, RCPSP. A critical review of the state of the art, based on the most significant papers published in the academic literature on this topic is carried out. Initially, several metaheuristic methods of solution are shown, especially those that have been implemented for sequencing problems, and their main characteristics, advantages and disadvantages are explained. Furthermore, the so-called sequence generating schemes and the complexity indices most commonly used are presented. Finally, the test library PSPLIB, used in most academic papers related to such problems is considered. MSC: 90B35

We carried out a comparative study of the thermal dilatation coefficient of molybdenum trioxide with and without Nd3+ doping. The doped samples were obtained from a solid state reaction of MoO3 and Nd2O3 in concentrations from 0.2 to 20.0at%. The prepared samples were analyzed as a function of the temperature through X-Ray diffraction (XRD), the chemical composition of the resultant material was studied using Energy Dispersive X-ray Spectroscopy (EDS). The results of the XRD show that the MoO3 doped with Nd in concentrations of 0.2 and 1.0% atomic grows iso-structurally with α-MoO3. Moreover, MoO3 doped with Nd3+ in concentrations of 5.0, 10.0 and 20.0% atomic exhibits the monoclinic phase Mo9O26. Finally, we determined that the values of the thermal expansion coefficient of MoO3, doped and un-doped, differ by less than 3%.

In this work we analyze the morphology, crystallographic and magnetic behaviors of molybdenum oxides doped with Nd thin films grown onto glass slide, through spray pyrolysis technique. The films were subjected to thermal treatments, after the fabrication, in oxygen from 2 to 20 hours. These were structurally analyzed by X-ray Diffraction (XRD), its chemical composition was determined by Energy Dispersive X-ray Analysis (EDX), and morphological evolution was evaluated through Scanning Electron Microscopy (SEM.The magnetic response was studied by DC magnetic susceptibility The XRD results show that the films obtained in different dissolution volumes and substrate temperatures of 300 degrees C present triclinic phases of molybdenum trioxide, deficient of oxygen (Mo9O26, Mo18O52). The films with thermal treatment have deficient oxygen phases and stoichiometric phases of MoO3. SEM results show that morphology of films changes with thermal treatment; the EDX study indicates that the films incorporate the Nd to the crystalline structure of the molybdenum oxide. Finally, films with 5% of Nd showed a paramagnetic response.

Thermoelectric properties of La1-xSrxCuO3-delta (LSCuO) samples prepared by sal-gel method were studied in the temperature range between 100 and 290 K From Seebeck coefficient S(T) and electrical resistivity p(T) measurements the thermoelectric power factor PF was calculated S(T) is positive over the studied temperature range suggesting a p type conduction its magnitude decreases with the Sr level from 400 mu V/K to 40 mu V/K The temperature dependence of p(T) changes from semiconducting-like to metallic as the strontium increases at room temperature p(T) exhibit values less than 17 m Omega cm The thermoelectric performance was evaluated through the PF parameter which shows maximum values close to 60 mu W/K-2 cm These results make these oxygen deficient ceramics promising thermoelectric material for low temperature applications (C) 2010 Elsevier B V All rights reserved

En este trabajo se prepararon películas delgadas de trióxido de molibdeno (MoO3) por la técnica de atomización pirolítica. Las películas fueron depositadas sobre sustratos de vidrio y obtenidas a partir de una solución precursora de Heptamolibdato de Amonio Tetrahidratado ((NH3)6Mo7O24.4H2O) 0.1 M. La temperatura del sustrato se mantuvo constante en 400 oC y se varío el volumen de la solución precursora. Las muestras se caracterizaron por difracción de Rayos X (XRD), espectroscopía infrarroja, Microscopía Electrónica de Barrido (SEM) y eléctricamente a través de medidas de resistividad eléctrica en función de la temperatura. Las muestras crecen con estructura cristalina correspondiente a la fase alfa del MoO3 con dirección preferencial de crecimiento a lo largo de los planos (0k0). Al aumentar el volumen de la solución precursora la superficie de las muestras se vuelve porosa. La resistividad en estas muestras cambia en un orden de magnitud cuando son expuestas a la atmosfera de CO. PACS: 81.05.Hd 72.80.Jc

Polycrystalline ceramics with nominal composition of Ca3-xYxCo4O9+δ (0≤x≤0.10) were grown using the citrate-complex method. Thermoelectric properties were studied using Seebeck coefficient S(T) and electrical resistivity ρ(T) measurements. These transport properties were studied in the temperature range between 100 and 290K. For low doping levels in Y substituted samples (x≤0.06) the magnitude of S(T) and ρ(T) decreases with yttrium content. The temperature behavior of S(T) and ρ(T) was interpreted in terms of the small-polaron hopping mechanism. From S(T) and ρ(T) data it was possible to calculate the thermoelectric power factor PF, which reaches maximum values close to 23 μW/K2-cm. These values become these compounds promissory thermoelectric compounds for use in low temperature thermoelectric applications.

Oxide ceramics with nominal composition of La0.8Sr0.2Co1-xMnxO3(0⩽x⩽0.05) were grown by using the citrate sol–gel method followed by high temperature sintering. The thermoelectric properties were studied in the temperature range between 100 and 290 K. The magnitude of Seebeck coefficient S(T) and electrical resistivity ρ(T) increases with the manganese doping level, reaching maximum values close to 180μV/K and 4mΩcm, respectively. On the contrary, the total thermal conductivity κ(T) decreases with the manganese content. The behavior of S(T) and ρ(T) was interpreted in terms of small-pollaron hopping mechanism. From S(T), ρ(T) and κ(T) data it was possible to calculate the dimensionless thermoelectric figure of merit ZT, which reaches maximum values close to 0.12; the structural and morphological properties of the samples were studied by powder X-ray diffraction analysis and scanning microscopy (SEM), respectively.