Optical investigations of La0.7Ca0.3-xKxMnO3 (x = 0.00, 0.05 and 0.10) probed by spectroscopic ellipsometry

Using spectroscopic ellipsometry, we have studied the optical properties of doped manganites at the paramagnetic state in polycrystalline La0.7Ca0.3-xKxMnO3 samples for (x = 0.00, 0.05 and 0.10) in the energy range of 3.2-5.5 eV at room temperature. The surface morphology of the samples was obtained by using atomic force microscopy (AFM). Refractive indices, extinction coefficients, the transmission ellipsometric parameters Ψ and Δ are investigated at different wavelengths. The study of the optical conductivity σ reveals that optical behaviour and the activated transport in the paramagnetic state of these materials are consistent with Jahn-Teller small polaron. In addition, the spectrum of the complex dielectric constant ε reveals peaks for all samples, the results may be explained by the presence of space charges from the strongly dipole-allowed O(2p)−Mn(3d) transition

Structural, electric and dielectric properties of Ni0.5Zn0.5FeCoO4 ferrite prepared by sol-gel

Ni0.5Zn0.5FeCoO4 spinel ferrite was elaborated using sol-gel technique. X-ray diffraction patterns indicate that sample has a cubic spinel type structure with Fd-3m space group. The change in Raman modes and relative intensity were observed due to ball milling and consequently to the decrease of particle size and cationic redistribution. The Raman spectra show peaks appearing at 450 and 490 cm−1 corresponding to T2g (2) and T2g (3), respectively. It may be noted that both of these modes shift toward the higher wavenumber with the substitution of Zn by Ni in Ni0.5Zn0.5FeCoO4 ferrite. Mössbauer spectroscopy analysis shows one tetrahedral A-site and two octahedral B-sites. Due to Zn doping, the hyperfine magnetic fields are much smaller than for CoFe2O4 and NiFe2O4 ferrites. The Jonscher’s power low was used to describe the ac-conductivity measurements. Frequency dependence of dielectric constant (ε″) and tangent loss (tan) display a dispersive behavior at low frequencies that can be explained by the Maxwell Wagner model and Koop's theory. Electric modulus formalism has used to study the relaxation dynamics of charge carriers. The complex impedance spectra (Nyquist plots) show well-defined semicircles which are strongly dependent on the temperature.publishe

Oxygen-vacancy-related giant permittivity and ethanol sensing response in SrTiO3-δ ceramics

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 SrTiO3-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 SrTiO3-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.publishe

Landau mean-field analysis and estimation of the spontaneous magnetization from magnetic entropy change

We investigated the critical exponents for the compounds La1-x□xMnO3 (x = 0.1; 0.2 and 0.3) prepared by the sol–gel method. Our samples show a second- order transition inferred from the positive slope, in accordance with the Banerjee Criterion. Using the slope of different models on the TC, the relative slope (RS) was traced. From this perspective, the best models for the three samples prove to be the mean field and the tricritical mean field models. This model is characterized by critical exponents β, γ and δ which are determined by many methods such as MAP, KF method and critical isotherm analysis. The theoritical methods and experimental results were in good agreement for the three compounds. The universality class has been shown. After determining the spontaneous magnetization for x = 0.2 from (-ΔSM) vs. M2, we detected a good agreement with those obtained from the classical extrapolation of Arrott curves (µ0H/M vs. M2). Furthermore, based on the magnetocaloric effect (MCE), Landau’s theory is valid for the compound x = 0.2.publishe

Structural, magnetic and vibrational characterization of the new organic-inorganic hybrid material, (C9H14N)2CoCl4

A new organic–inorganic hybrid material, bis (N, N-dimethylbenzylammonium) tetrachlorocobaltate (II), (C9H14N)2 CoCl4 was synthesized and analyzed by X-ray diffraction. Magnetization was used to investigate the magnetic properties. The structure was determined at room temperature in the triclinic space group P-1 with the following parameters: a = 10.491 (5)Å, b = 14.207 (2)Å, c = 16.187 (3)Å, α = 87.76 (3)°, β = 88.436 (8)°, γ = 89.897 (10)° and Z = 2. The structure can be described by the alternation of organic-inorganic layers parallel to (110) plan. The different components are connected by the Nsingle bondH⋯Cl hydrogen bonds between the cation and the anionic group [CoCl4]2-. Raman and infrared spectra were used to gain more information of the title compound. An assignment of the observed vibration modes is reported. This compound exhibits an antiferromagnetic (AFM) to paramagnetic (PM) phase transition at a temperature (TN) lower than 2 K. The values of paramagnetic Curie–Weiss temperature θCW, the nearest neighbor interaction Jnn, the classical nearest neighbor J cl and the dipolar Dnn interactions’ emphasize the existence of an antiferromagnetic interaction between the neighboring cobalt ions.publishe

Investigating the structural, morphological, dielectric and electric properties of the multiferroic (La0.8Ca0.2)0.9Bi0.1FeO3 material

The (La0.8Ca0.2)0.9Bi0.1FeO3 (LCBFO) compound has been synthesized by the sol-gel method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Raman spectroscopy and electrical impedance spectrometry. XRD results revealed that (La0.8Ca0.2)0.9Bi0.1FeO3 crystals are orthorhombic, belonging to the Pnma space group. The SEM measurements showed that the sample presents a large distribution of nano-grains connected to each other. The relaxation process and the electrical conductivity are awarded to the same type of charge carriers characterized by similar values of the activation energy determined from loss factor tangent tg δ( ), the imaginary part of the permittivity and from the Modulus spectrum. The ac-conductivity was analysed to examine the conduction mechanism, using the Jonscher’s universal power-law given by: = +σ ω σ Aω( )ac dc s. Based on the parameter s behavior, the conductivity was studied according to the NSPT model (non-overlapping small polaron tunneling).publishe

Effect of annealing temperature on structural, morphology and dielectric properties of La0.75Ba0.25FeO3 perovskite

The effect of annealing temperature on the structure, morphology and dielectric properties of La0.75Ba0.25FeO3 compound prepared by the sol-gel method was investigated. The increase of the annealing temperature from 900 to 1100 °C, promotes an increase of the average grain size value. Two dielectric relaxations are detected using the dielectric modulus formalism, attributed to grain and grain boundary relaxations. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance and Modulus results at different measuring temperatures. The ac conductivity could be described by Jonscher's power law revealing the presence of both overlapping large polaron tunneling and non-overlapping small polaron tunneling mechanisms.publishe

Stapling and Section of the Nasogastric Tube during Sleeve Gastrectomy: How to Prevent and Recover?

Bariatric surgery has become an integral part of morbid obesity treatment with well-defined indications. Some complications, specific or not, due to laparoscopic sleeve gastrectomy (LSG) procedure have recently been described. We report a rare complication unpublished to date: a nasogastric section during great gastric curve stapling. A 44-year-old woman suffered of severe obesity (BMI 36.6 kg/m2) with failure of medical treatments for years. According to already published technique, a LSG was performed. Six hours postoperatively, a nurse removed the nasogastric tube according to the local protocol and the nasogastric tube was abnormally short, with staples at its extremity. Surgery was performed with peroperative endoscopy. In conclusion, this is the first publication of a nasogastric section during LSG. Therefore we report this case and propose a solution to prevent its occurrence. To avoid this kind of accident, we now systematically insert the nasogastric tube by mouth through a Guedel cannula. Then, to insert the calibrating bougie, we entirely withdraw the nasogastric tube

Controllable synthesis, XPS investigation and magnetic property of multiferroic BiMn2O5 system: The role of neodyme doping

In this work, a novel series of multiferroic materials BiMn2O5 doped by Neodyme has been prepared by a sol-gel method at low temperature. The crystallographic studies using X-ray diffraction and Rietveld Refinement techniques showed the formation of single-phase samples for all compositions, crystallizing in a mullite-type orthorhombic perovskite structure, space group Pbam (Z=4). The SEM techniques confirmed the formation of single-phase materials with excellent mapping distribution. Raman and infrared spectroscopic measurements were performed and combined with lattice dynamics simulations to describe the room-temperature vibrational properties of all samples. The X-ray Photoelectron Spectroscopy (XPS) were measured in the energy range of 0–1400 eV at room temperature. The Fermi level EF was defined with the accuracy of 0.127, 0.32 and 0.48 eV for BiMn2O5, Bi0.9Nd0.1Mn2O5 and Bi0.8Nd0.2Mn2O5 respectively. The X-ray photoelectron spectroscopy shows the existence of Mn4+ state. Magnetic measurements indicate Neél temperature TN at 31, 40 and 61 K for BiMn2O5, Bi0.9Nd0.1Mn2O5 and Bi0.8Nd0.2Mn2O5 respectively