Search

The plot of dε′/dT versus temperature for the (La0.8Ca0.2)0.4Bi0.6FeO3 material proves four dielectric anomalies at 180 K, 240 K, 320 K and 350 K with a colossal dielectric constant at low frequency allowing its application in energy storage devices.

This paper describes the realization and characterization of $${\text{La}}_{0.8}{\text{Pb}}_{0.1}{\text{Ca}}_{0.1}{\text{Fe}}_{1-x}{\text{Co}}_{x}{\text{O}}_{3}$$ gas-based sensors. $${\text{La}}_{0.8}{\text{Pb}}_{0.1}{\text{Ca}}_{0.1}{\text{Fe}}_{1-x}{\text{Co}}_{x}{\text{O}}_{3}$$ $$(0.00\le x\le 0.20)$$ thin films are prepared using the drop-coating method over a $${\text{Si}}/{\text{SiO}}_{2}$$ substrate with inter-digitated $${\text{Pt}}$$ -electrodes. The sensors, thus, produced exhibit a good sensitivity to ozone at low concentration. The substitution of iron atoms by cobalt ones increases the sensor responses “S,” from 1.716 for $$x = 0.00$$ to 6.584 to $$x = 0.20$$ for an ozone concentration equal to $$400\,{\text{ppb}}$$ . In addition, the substitution of iron by cobalt induces a decrease in the sensor-operating temperature from $$270\,^\circ{\text{C}}$$ for the parent compound $$(x = 0.00)$$ to $$170\,^\circ{\text{C}}$$ for $$x = 0.20$$ .

Generation of Digital Elevation Models (DEMs) using Synthetic Aperture Radar (SAR) data is a valid flexible alternative to other surveying techniques. In this work we adopt radargrammetry on two SAR images recorded by the Capella Space X-band spaceborne sensor on two consecutive days over La Palma Island (Canary Islands, Spain) during the Cumbre Vieja volcanic eruption, with the aim of investigating the potential of these high-resolution (up to 0.7 by 0.5 m2) SAR images in generating precise DEMs. The adopted method employs a multilook-based spatial filter followed by an iterative region-growing algorithm to identify matching pixels between the two images. The resultant radargrammetric DEM is compared with a Lidar-based DEM, showing a good agreement in the areas less affected by lava flow. © 2022 IEEE.

La1−2xBaxBixFeO3 (0.00 ≤ x ≤ 0.20) nanoparticles were prepared by the auto-combustion method using glycine as a combustion fuel. X-ray diffractometry (XRD) measurements confirmed the orthorhombic structure of the synthesized compounds with the Pnma space group as a principal majority phase and showed the presence of a very minor secondary phase when x > 0.1. The nanosize criterion of the prepared compounds was confirmed from the crystallite size values calculated using the Williamson–Hall formalism. The relaxation process has been studied by the frequency dependence of the imaginary parts of impedance and modulus (Z′′ and M′′) which satisfied the Arrhenius law. Nyquist plots allowed us to obtain an adequate equivalent circuit involving the grains and grain boundary contributions. The activation energies calculated from Z′′, M′′ and the resistance of both contributions deduced from the Nyquist plots are found to be very similar. The conduction mechanism has been analyzed using the temperature dependence of the exponent Jonscher's power law parameter which confirms the NSPT conduction mechanism type for all compounds with an enhancement of the binding energy of the charge carrier (WH) with the substitution.

Nanocrystalline gas sensitive material based on Perovskite type La0.8Ca0.1Pb0.1FeO3 (LCPFO) sample has been prepared by the sol-gel method with the citric acid route. The gas sensitivities under different temperatures of the (LCPFO) compound have been investigated toward the two NH3 and CO reducing gases. The synthesized compound has been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). It was found that the compound exhibits an orthorhombic symmetry with the Pnma space group. The effect of the experiment environment (under vacuum and air) on the conductance and activation energy Ea of the LCPFO compound has been evaluated. The Ea values have been found to be in the range of 0.43 eV

The La0.8Ba0.1Ce0.1FeO3 compounds were prepared by the auto-combustion route and annealed at two different temperatures to study their effect on the structural, morphological and dielectric properties of the Barium- and Cerium-substituted LaFeO3 compound. The X-ray diffraction analysis revealed that both compounds crystallized in the orthorhombic structure belonging to the Pnma space group. The rise of the annealing temperature from 700 to 900 °C was found to lead to the increase of the average grain size value as characterized by SEM. Furthermore, two clear relaxations phenomena have been detected using the Nyquist and Argand’s plots of dielectric impedance and Modulus curves at different temperatures, which are attributed to both grain and grain boundary contributions. Their activation energies have been calculated not only from the frequency dependence of both imaginary parts of impedance (Z″) and modulus (M″) but also from the contribution of the resistances deduced from the Nyquist plots. These plots have been adjusted using two circuits in series, each of which containing a resistance in parallel to a CEP capacitance. The conduction mechanism was analyzed by ac conduction using the Jonscher’s power law. The NSPT conduction model has been confirmed for both compounds in which the rise in heat treatment decreases the binding energy of carriers.

Two compounds with the formula La0.8Ba0.1Bi0.1FeO3 have been prepared by the sol–gel (LBBFO-SG) and the auto-combustion (LBBFO-AC) preparation methods. The effect of the preparation method on structural, morphology, vibrational, electrical, and dielectric properties have been carried out using the X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Raman and impedance spectroscopy. The Rietveld refinement of the XRD diffractograms confirms the crystallization of both compounds through the Pnma space group. Furthermore, the nano-size scale of the prepared compounds was verified by the XRD and the SEM microscopy. From the Raman study, we conclude that the vibration modes are similar to those of the pure LaFeO3 with a slight shape change in some modes. The relaxation processes were analyzed with the Bergmann formalism to validate the presence of two relaxation processes corresponding to grains and boundary grains contributions. These relaxations have been confirmed by studying the dielectric constant also the dielectric loss tangent is used to study the ferroelectric–paraelectric phase transition at around room temperature. The activation energy for both contributions has been calculated from the impedance, the modulus, and the dielectric loss tangent and they have almost the same values. The Nyquist plots (Z″ vs. Z′) have been adjusted using two circuits in series containing each one a resistance in parallel to a CEP capacitance.

The perovskite (La0.8Ca0.2)1−xBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) LCBFO compounds were synthesized by the sol–gel method using the citric acid route and sintered at 800 °C (LCBFO800) and 900 °C (LCBFO900). The structural properties studied by X-ray diffraction (XRD) revealed that all the compounds present the same crystallographic structure confirmed by the superposition of all the characteristic peaks. The slight deviation of the XRD peaks towards the weakest angles informed us that the volume of the elementary mesh increases as a function of the rate of substitution (bismuth). This observation, which is obviously valid for the two series, confirmed that the annealing temperature has no influence on the structure. Scanning electron microscopy (SEM) micrographs showed that the morphology of the samples is characterized by the presence of large agglomerates. Although, transmission electron microscopy (TEM) characterization confirmed the nano-sized grains. These two characterization techniques revealed that the LCBFO800 series presents the smallest grain size. The magnetic study exposed that all the samples (LCBFO800 and LCBFO900) show a weak ferromagnetic behavior (unsaturated hysteresis curves) and an increase in magnetization (M) with increasing Bi-content, with a higher M value for a lower annealing temperature. The Curie temperature is smaller in the case of LCBFO800 compounds and decreases with the insertion of Bi.

(La0.8Ca0.2)1−xBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) (LCBFO) multiferroic compounds have been prepared by the sol–gel method and calcined at 800 °C. X-ray diffraction results have shown that all samples crystallise in the orthorhombic structure with the Pnma space group. Electrical and dielectric characterizations of the synthesized materials have been performed using complex impedance spectroscopy techniques in the frequency range from 100 Hz to 1 MHz and in a temperature range from 170 to 300 K. The ac-conductivity spectra have been analysed using Jonscher's power law σ(ω) = σdc + Aωs, where the power law exponent (s) increases with the temperature. The imaginary part of the complex impedance (Z′′) was found to be frequency dependent and shows relaxation peaks that move towards higher frequencies with the increase of the temperature. The relaxation activation energy deduced from the Z′′ vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the relaxation process and the conduction mechanism may be attributed to the same type of charge carriers. The Nyquist plots (Z′′ vs. Z′) at different temperatures revealed the appearance of two semi-circular arcs corresponding to grain and grain boundary contributions.

Correction for ‘Effect of the annealing temperature and of Bi substitution on the structural and magnetic behaviors of double-doping (Bi/La, Ca) (La0.8Ca0.2)1−xBixFeO3 compounds’ by H. Issaoui et al., New J. Chem., 2020, 44, 9813–9821, https://doi.org/10.1039/D0NJ01962C.

In this work we synthesized the multifunctional (La

La

International audience; In this study, La0.8Pb0.1Ca0.1Fe1−xCoxO3 (x = 0.10 and x = 0.20) thin films with respective thicknesses of 300 and 600 nm have been prepared by the drop coating technique onto a Si/SiO2 substrate with platinum interdigitated electrodes. The effects of cobalt-content and film thickness on the ozone sensing properties have been studied. The sensor responses have been determined in an operating temperature range between 160 and 280 °C. Sensors have been exposed to different concentrations between 50 and 400 ppb of ozone gas at a constant flow rate of 500 ml min−1 dry air. The studied La0.8Pb0.1Ca0.1Fe1−xCoxO3 (x = 0.10 and x = 0.20) compounds could be a promising sensitive film for ozone detection, especially for the thinnest sensitive layer, 300 nm in our case.

La técnica Persistent scatterer (PSI) basada en datos SAR interferométricos se ha consolidado como una importante herramienta de monitoreo de los movimientos de la superficie terrestre. Un claro ejemplo de esto ha sido la aparición de varios servicios regionales/nacionales e incluso continentales para el monitoreo sistemático de movimientos del terreno. El proyecto European Ground Motion Service generará un mapa de desplazamiento en toda Europa una vez al año. Pese a la consolidación de la técnica, su uso operativo todavía está en manos de usuarios con la experiencia suficiente para interpretar correctamente los resultados PSI. La generación de herramientas y metodologías que faciliten la gestión de la enorme cantidad de datos por analizar y su análisis es fundamental. Las ADATools son un primer paso en esta dirección. Son herramientas sencillas y rápidas para extraer de forma automática y proporcionar una interpretación preliminar de las principales Áreas de Deformación Activa (ADA) detectadas. ADATools incluye: (i) el ADAFinder, que detecta las ADA principales, las delimita espacialmente y les asigna un índice de calidad; (ii) LOS2hv, se usa en caso de que tengamos mapas de geometrías ascendentes y descendentes para derivar la componente horizontal (este-oeste) y vertical del movimiento; (iii) el ADAClassifier que se encarga de clasificar preliminarmente en base al tipo de movimiento esperable. En esta presentación, se presentan los procedimientos utilizados por el ADATools y algunos ejemplos de aplicación. En concreto, se comentarán algunos resultados sobre una zona de la región de Granada, conseguidos en el marco del Proyecto RISKCOAST (Ref: SOE3/P4/E0868) (Programa Interreg Sudoe a través del Fondos FEDER).

The effect of 5% magnesium doping on the structural, magnetic and gas sensing properties of La0.8Ca0.1Pb0.1Fe0.95Mg0.05O3 (LCPFMO) has been investigated. The nanosize compound was prepared by the Sol–Gel method, using the citric acid route. The Structural study confirms that this compound crystallizes in the orthorhombic structure with the Pbnm space group. From the magnetic measurements, we were able to show that the effect of the Mg doping is to increase the saturated magnetization and to decrease the Ferromagnetic–Paramagnetic magnetic phase transition temperature (TC). A theoretical modulation was derived in order to confirm the domination of the ferromagnetic contribution over the Antiferromagnetic one. The AC-conductivity dependence on both temperature and frequency was studied; the study confirmed the presence of two behaviors; at high-temperature region, it was found to be only temperature dependent, while at low temperatures, it depends on both frequency and temperature parameters. At low temperature, the conduction mechanism is studied according to the NSPT model, where all parameters were discussed. The electrical Sensitivity (S) of the prepared sample to different ethanol gas concentration was investigated, using a broadband dielectric spectroscopy. It was found that 5% of magnesium insertion leads to an improvement in the sensitivity of the LCPFMO sample. This sensitivity was found to be ethanol amount dependent.

A spinel ferrite sample Zn0.4Ni0.6Fe2O4 was prepared by a conventional solid-state reaction method at high temperature. This compound was found to exhibit a single phase and crystallize in a cubic structure with Pm3 m Space group. The complex impedance was investigated in the temperature range 400–700 K and in the frequency range 100 Hz - 1 MHz. The Z-impedance analysis revealed that the relaxation phenomenon is strongly dependent on temperature and frequency. The impedance plane plot showed semi-circle arcs at different temperatures, and a proposed electrical equivalent circuit explained its results. The temperature and frequency dependence of the ac conductivity was shown to obey the universal Jonscher's power law. The activation energy, inferred from the impedance spectrum, was confirmed to match very well with those estimated from the conduction mechanism, indicating that the relaxation process and conductivity have the same origin. The magnetization is due to the ferromagnetic interactions between iron ions.

To explore the relationship between optical properties, oxygen vacancies and magnetism in SrTiO3, we prepared a series of SrTiO3-δ (δ = 0.00, 0.125 and 0.250) samples by solid state reaction method followed by the creation of oxygen vacancies-δ. Surface composition and chemical valence state in the synthesized compounds were examined by X-ray photoelectron spectroscopy (XPS). The Fourier Transform Infrared spectroscopy (FT-IR) spectra showed that the transmission properties change with oxygen vacancies introduction. Ultraviolet–visible absorption revealed that optical properties were highly dependent on oxygen vacancies concentrations. When the magnetic field was applied, magnetization showed weak-ferromagnetism at room temperature on SrTiO3-δ non-stoichiometric systems. Yet, it was reversed showing diamagnetism on SrTiO3 perfect crystal. The large concentration of oxygen vacancies (δ = 0.250) reduced ferromagnetism and optical absorption, implying the possible presence of a relationship between the magnetism and the optical properties. Theoretical results showed two types of electronic contributions to magnetism, one of which emanates from localized states below the conduction band minimum, and the other comes from itinerant electrons of Ti atoms lying further away from the oxygen-vacancy. The electronic structures and magnetic properties were calculated by Full-Potential Linear Augmented Plane Wave (FP-LAPW) method within the Generalized Gradient Approximation (GGA) and the atomic relaxations introduced by the oxygen vacancies host in a fully self-consistent way. The results shed some light on the promising magneto-optical properties of the SrTiO3-δ materials.

The ethanol sensing properties of SrTiO3-δ (δ = 0.075 and 0.125) ceramics was analyzed by dielectric measurements. The ceramics were prepared by solid state reaction method followed by the creation of oxygen vacancies- δ , through a thermal activated process. The crystal symmetry, space group and unit cell dimensions were derived from the X-ray diffraction (XRD) data using FullProf software whereas grain's size distribution was assessed by scanning electron microscopy (SEM). The prepared samples have been analyzed by impedance spectroscopy over the frequency range from 100 Hz to 1 MHz and temperature range from 240 to 340 K. The dielectric properties of SrTiO 3-δ ceramics showed a quite remarkable stability of giant permittivity (>104 ) as well as a low dielectric loss , which open ways for several applications such as over voltage protections of electronic devices. A low-frequency dielectric relaxation behavior was found, and the carriers for electrical conduction result from the first-ionization of oxygen vacancies . The conductivity and gas sensitivity of SrTiO 3-δ-based sensors were investigated. Results demonstrated that the conductivity decreases after the introduction of the ethanol gas, and p-type semiconductor gas-sensing materials were obtained. Both characteristics present higher responses at lower optimal operating temperatures.

We have investigated the effect of multi-doping in A and B site of the multiferroic prepared by the Sol-gel method Bi0.8Er0.1Ba0.1Fe0.96Co0.02Cr0.02O3 (BEBFCC) on the structural, morphological and electric properties. X-Ray diffraction and Rietveld refinement confirm that the BEBFCC compound presents a rhombohedral structure with the R3C space group. The Ac electrical properties have been measured from 331 to 735 K as a function of frequency (100 kHz - 1 MHz). Debye's theory and Arrhenius relations were used to study the relaxation phenomenon. The frequency dependence of the impedance (Z”: imaginary part) reveals the existence of one relaxation peak, while the Modulus formalism shows two peaks. The presence of two contributions, related to the dielectric relaxations visible in this compound, was confirmed by the Impedance Nyquist plots. The study of the ac conductivity based on Jonsher's power law confirms that the conduction is associated to the Non-Overlapping Small Polaron Tunneling model.

The magnetic properties, Mossbauer and the critical behavior of the compound Bi0.8Ba0.1Er0.1Fe0.96Cr0.02Co0.02O3 prepared by sol-gel are the subject of this study. The compound has an R3c structure and exhibits a ferromagnetic to paramagnetic phase transition c.a. 574 K. A theoretical adjustment of the hysteresis cycles at room temperature show two magnetic contributions: Ferromagnetic (FM) and Antiferromagnetic (AFM) with a predominance of the first contribution. Mossbauer spectroscopy revealed two Fe3+ cations differently coordinated. Magnetic measurements versus magnetic field reveal that the sample exhibits a second order magnetic phase transition. The Curie temperature ​​and the critical exponents (β, γ and δ) were determined by different techniques. These values are in agreement with the ones predicted by the mean field model.

(La

The effect of Bi doping of (La0.8Ca0.2)1-xBixFeO3 perovskites on structural and magnetic properties was investigated. X-ray diffraction, magnetometry and Mossbauer spectroscopy measurements were performed on the samples. The sol gel prepared samples were annealed at 800 °C, 900 °C and 1200 °C. The samples crystallize in an orthorhombic structure with a PNMA space group. The LCBFO800 samples have Mossbauer spectra with large sextets in accordance with the small grain size. The several spectral components observed in the sample series are in accordance with the ones found in literature. Hyperfine magnetic fields decrease slightly with Bi content and increase with annealing temperature. Isomer shifts and quadrupole splitting stay constant with composition and annealing temperature. Magnetometry measurements show that the antiferromagnetic behavior is dominate over the ferromagnetic one. Bi doping increases coercivity and decreases remanent magnetization, while annealing temperature increases coercivity and remanent magnetization.

The nano-materialsLa0.8Ca0.1Pb0.1Fe1−xCoxO3 (x = 0.00 to 0.20) were prepared by the sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray dispersion (EDS). The structure refinement of the XRD data was performed using the Rietveld method. These compounds were found to exhibit a single phase and crystallize in the orthorhombic structure with Pnma space group. The chemical analysis by EDS shows the successful incorporation of Co (Cobalt) in the parent sample. The volume was found to decrease with the increase of the cobalt-content. The volume decrease was also investigated theoretically by comparing the total energies of LaFeO3 and LaCoO3 compounds which were calculated within density functional theory (DFT). We find an almost agreement between experimental and theoretical results, provided we use the correct SGGA + U functional (in contrast to the SGGA–Spin polarized Generalized Gradient Approximation), which takes properly into account the strong electron correlation in the open d-shell by a Hubbard-like U term. Our analysis of the corresponding densities of states indicates a qualitatively different ground state behavior of the Fe- or Co-ion.

(La0.8Ca0.2)1−xBixFeO3 (x = 0.0, 0.1, and 0.2) compounds were prepared by the sol-gel method, using the citric acid route. Structural and microstructural characteristics of the samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Mossbauer spectroscopy was also used for magnetic characterization and structural confirmation of X-ray data. Refinement of XRD patterns indicated that the compounds crystallize in an orthorhombic structure, Pnma space group. The SEM measurements showed that the morphology of the samples is characterized by the existence of large agglomerates, while TEM confirmed the fine particle size. Raman spectra revealed that, when increasing temperature, the level of oxygen species adsorbed at the surface of the particles increases progressively. Room temperature Mossbauer spectroscopy data revealed the existence of two octahedral magnetic sites in the structure of the compounds, which is compatible with XRD data, and a small percentage of a paramagnetic phase in the samples, which increases with Bi-content.

Strontium titanate was prepared by solid-state reaction method. According to the XRD, it was single phase and has a cubic perovskite structure. The Raman spectroscopic investigation was carried out at room-temperature, and the second-order Raman modes were observed. By employing impedance spectroscopy , the dielectric relaxation and electrical properties were investigated over the temperature range of 500–700 K at various frequencies. The activation energies evaluated from dielectric and modulus studies are in good agreement and these values are attributed to the bulk relaxation. The impedance data were well fitted to an (R 1//C1)-(R2//CPE1) equivalent electrical circuit. It could be concluded that the grain boundaries are more resistive and capacitive than the grains. The ac conductivity was found to follow the Jonscher's universal dynamic law ωS and the correlated barrier hopping model (CBH) has been proposed to describe the conduction mechanism.

In the present paper, the La1–2xBaxBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) nanosized perovskite materials have been successfully prepared by the auto-combustion route using the glycine as fuel. The structural, morphological, and gas sensing properties of these samples have been investigated. The Rietveld refinement has revealed a single orthorhombic phase (Pnma space group) for the compounds with x ≤ 0.10, while the samples with x = 0.10 and 0.20 have been found to contain a minor amount of two secondary phases. We have confirmed that the La0.8Ba0.1Bi0.1FeO3 (x = 0.10) compound possesses the smallest average particle size (34.58 nm) with the purely orthorhombic structure and exhibits a high surface roughness, as determined by atomic force microscopy measurements. Importantly, the gas sensing tests have been carried out for all prepared compounds with different ethanol and H2S gas concentrations (from 5 to 100 ppm). The La0.8Ba0.1Bi0.1FeO3 (x = 0.10) compound has been proven to exhibit excellent performance in ethanol and H2S gas response even for very low concentrations (5 ppm) with an optimum operating temperature of 180 and 200 °C, respectively. Furthermore, the response and recovery times analyzed for both these gases were found to be very short (between 5 and 10 s).

Two nanoparticle orthoferrite materials (La0.8Ca0.2)0.9Bi0.1Fe1−yTiyO3 (y = 0.0 and 0.1) have been successfully synthesized via the assisted ball milling solid-state reaction. The effect of Bismuth and Titanium ions insertion in A and B-sites of La0.8Ca0.2FeO3 material on structural, dielectric relaxation and magnetic properties was conducted. Structural study reveals the formation of majoritarian orthorhombic phase in both nanomaterials. Importantly, both compounds present a giant dielectric constant e’ and low dielectric loss tangent tg(δ). Two relaxation processes have been detected at low and high-temperature ranges. The adjustment of the imaginary parts of complex Modulus via the Havriliak-Negami formalism (H-N) confirms a Cole-Cole (grains) and Cole-Davison (grain boundaries) relaxation processes at low and high temperature regions, respectively. The magnetic study reveals the enhancement of magnetization when introducing Titanium ions in B-site which increases the Ferromagnetic interactions. It also confirms an important decrease in the Curie Weis temperature (TC = 450 K).

Polycrystalline SrTiO 3- δ powders with cubic perovskite phase were prepared by solid-state reaction method followed by the creation of oxygen vacancies δ- thermal activated. The Raman spectroscopic investigation was carried out in a frequency range of 100–2000 cm −1 , and the second-order Raman modes were observed at room temperature. The Electron Paramagnetic Resonance (EPR) results revealed that SrTiO 3- δ samples had evident EPR signals that increased significantly with oxygen-vacancy concentrations. The incorporation of oxygen vacancies was found to decrease the thermal resistivity. Besides, the electrical sensing measurements showed that sensors based on SrTiO 2.925 (STO1) and SrTiO 2.875 (STO2) exhibited semiconductor behavior, while SrTiO 2.75 -based sensor (STO3) revealed the introduction of a metallic behavior at low temperature. Furthermore, these measurements confirmed that the resistivity increased after the introduction of the ethanol gas, which indicates that our samples can be considered as sensors for ethanol gas detection. The formation of oxygen vacancies under ethanol exposure at the surface of SrTiO 3- δ sensors was evaluated by photoluminescence.

SrTiO3-δ (δ = 0.075, 0.125 and 0.25) were prepared in two steps: the preparation of the parent compound SrTiO3 by the solid state reaction method followed by the creation of oxygen vacancies δ, through a thermally activated process. X-ray diffraction analysis shows that all samples crystallize in the cubic structure with Pm3m space group. The grain's size distribution and the samples' surface characteristics were assessed by scanning electron microscopy. Impedance spectroscopy was used to characterize the ac electrical properties of these materials as a function of frequency at various temperatures (240–340 K). The impedance data was well fitted to an (R1CPE1)//(R2CPE2) equivalent electrical circuit model. It was found that the electrical behavior of the ceramics is dominated by the grain-boundary response and increased conductivity values were found for a large amount of oxygen vacancy. The frequency dependence of the conductivity was investigated through the Jonscher's universal power law and the electrical conduction mechanism was found to be strongly dependent on the oxygen vacancies concentration.

The critical behavior associated with the magnetic phase transition has been investigated by magnetization isotherms in La 0.6 Ca 0.4− x Sr x MnO 3 nano-particle compounds for x = 0 (S0C1), 0.05 (SC. 4-4) and 0.4 (S1C0). The critical exponents are estimated by various techniques, such as the Modified Arrott plot, Kouvel–Fisher plot and critical isotherm techniques. Thus, the average values of the critical exponent and the critical temperature obtained by the different methods are ( β m o y = 0.47 ; γ m o y = 1.02 ; δ m o y = 3.00 ; T C = 230.6 K ) for S0C1, ( β m o y = 0.47 ; γ m o y = 1.00 ; δ m o y = 3.21 ; T C = 361.9 K ) for S1C0, and ( β m o y = 0.26 ; γ m o y = 1.02 ; δ m o y = 4.92 ; T C = 286.4 K ) for SC. 4-4. These values are in good agreement with those given by the theoretical models: Mean-Field model ( β = 0.5, γ = 1 and δ = 3) for S0C1 and S1C0 compounds; and Tricritical mean-Field model ( β = 0.25, γ = 1 and δ = 5) for SC. 4-4 one. The reliability of the critical exponent values was confirmed by the Widom scaling relation and the universal scaling hypothesis.

El propósito de este trabajo es analizar la relación entre la ciencia política y la administracion pública, su grado de influencia en los resultados de la gestión y determinar si los administradores públicos pueden actuar con un perfil eminentemente técnico o si es condicionante básico contar con su alineación política para el desarrollo eficiente de los objetivos del gobierno, como parte de la estrategia para el desarrollo de los planes. El alcance de este estudio abarca el análisis teórico de la doctrina de la administración pública y la ciencia política, asi como la evaluación de la aplicación práctica en el manejo de la gobernabilidad en los gobiernos locales de la costa de la Provincia del Guayas. Los resultados de la investigación se demuestran en cuadros comparativos y permiten evaluar que entre estas dos ciencias hay una relación estrecha que no es posible divorciar sin atentar con las estrategias de gobernabilidad de los gobiernos de turno.

We study in this paper the macroscopic hardness of TiB 2 and TmB 2 compounds and their corresponding ternary alloys Tm 1−x Ti x B 2 by calculating the mechanical properties and electronic structure of these systems. The mechanical results show that TiB 2 compound is found ultra-hard compared with TmB 2 and the covalent B B bonds have an enormous impact on the macroscopic hardness of these systems. These results are in excellent agreement with experiment. In addition, a large charge density was observed in the TiB 2 compound comparing to that of TmB 2 and of the considered alloys. For short interatomic distances B B, the hardness in Tm 1−x Ti x B 2 alloys is important.