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

Rare earth elements, iron and manganese in ochre-precipitates and wetland soils of a passive treatment system for acid mine drainage

The rare earth elements (REE) along with iron and manganese distribution in ochre-precipitates and wetland soils in a passive system for acid mine drainage treatment (Jales, Portugal) was studied. The results obtained by instrumental neutron activation analysis showed a higher incorporation of the light REE (particularly La and Ce) by the ochre-precipitates resulting from the mine water-limestone interaction. These fluffy materials influence the entrance of the first wetland where a correlation between Fe and La and Ce was found. Then Mn phases appear to play a more important role controlling REE distribution in the remaining area of the wetland soils.Thanks to EDM (Empresa de Desenvolvimento Mineiro, S.A.) for providing access to the water treatment plant, and to the staff of the Portuguese Research Reactor (RPI) of CTN/IST. C2TN authors gratefully acknowledge the FCT (the Portuguese Science and Technology Foundation) support through the UID/Multi/04349/2013. This work is co-funded by European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and national funds provided by FCT.info:eu-repo/semantics/publishedVersio

Synthesis, structural characterization and broadband ferromagnetic resonance in Li ferrite nanoparticles

Lithium ferrites are well known materials due to its numerous technological applications especially in microwave devices. Lithium ferrite nanoparticles were prepared by sol-gel technique by means of Pechini method, and then annealed at different temperatures in 250–1000 °C range. XRD confirms spinel formation with particles sizes in 15–700 nm range, with increased size with annealing temperature, whereas FTIR and Raman measurement confirm that single phase lithium ferrite with ordered cationic structure is obtained. Microwave magnetoabsorption data of the annealed lithium ferrite nanoparticles were obtained with a broadband system based on a network analyzer that operates up to 8.5 GHz. At fields up to 200 mT we can observe a broad absorption peak that shifts to higher frequencies with magnetic field according to ferromagnetic resonance theory. The amplitude of absorption, up to 85%, together with the frequency width of about 5.5 GHz makes this material suitable as wave absorber. FMR parameters like resonance field, linewidth and broadening are analyzed in order to obtain the characteristic parameters and analyze the microwave behaviour.publishe

Sumos detox e efeitos na saúde: perceção do consumidor

Os sumos detox são uma nova tendência alimentar e estão associados a um estilo de vida saudável. São utilizados como substitutos de refeições ou mesmo de um ou mais dias alimentares. Consoante os ingredientes que fazem parte da sua constituição são-lhes atribuídos diversos benefícios como: fonte de vitaminas e minerais, poder desintoxicante, poder drenante e coadjuvantes na eliminação de gorduras e perda de peso. O objetivo deste trabalho foi avaliar a perceção do consumidor relativamente aos efeitos na saúde associados ao consumo de sumos detox. Foi desenvolvido e aplicado um questionário online, disponibilizado por e-mail e através das redes sociais. Este questionário foi aplicado a 285 indivíduos com idades compreendidas entre os 18 e os 84 anos, dos quais 76,1% pertencem ao sexo feminino e 23,9% ao sexo masculino. De acordo com os resultados obtidos, verificou-se que 97,9% dos inquiridos já ouviram falar em sumos detox mas apenas 90,2% sabem no que estes consistem. Relativamente ao seu consumo, 48,8% dos inquiridos já os consumiram pelo menos uma vez e 51,2% nunca os experimentaram. As principais vantagens associadas a estes sumos foram: poder desintoxicante (64,9%), capacidade de repor os constituintes em défice no organismo, como vitaminas e minerais (56,8%) e capacidade drenante (35,1%). Os resultados indicam também que 67,4% da população inquirida considera que estes sumos não constituem uma boa opção para substituir refeições uma vez que não fornecem os nutrientes necessários ao organismo (56,8%), não fornecem a energia necessária (38,5%) e/ou não são saciantes (24,9%). Dos 32,6% que os consideram adequados para serem utilizados como substitutos de refeições, 68,8% refere o seu consumo a meio da manhã apropriado para este efeito. Os benefícios nutricionais associados, com maior frequência, a estes sumos foram a sua riqueza vitamínica (80,7%) e o seu poder de hidratação (61,4%). Em conclusão, verificou-se que a maioria da população inquirida já ouviu falar em sumos detox mas apenas metade já os consumiu, pelo menos uma vez. A maior parte dos inquiridos considera que estes não constituem uma boa opção para substituir refeições mas associam-lhe diferentes tipos de benefícios.Este trabalho foi financiado pelo INSA no âmbito do projeto BioCOMP (2012DAN730). Tânia Gonçalves Albuquerque agradece a Bolsa de Doutoramento (SFRH/BD/99718/2014) financiada por FCT, FSE e MEC.info:eu-repo/semantics/publishedVersio

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

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

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

Impact of the pulling rate on the redox state and magnetic domains of Fe-Si-O glass ceramic processed by LFZ method

This work studies the effect of the pulling rate, varying from 100 to 400 mm/h, on the redox state, structure and magnetic properties of iron oxide bearing silica glasses processed by laser floating zone (LFZ) method. XRD analysis revealed that the maximum crystallinity is obtained in the fibre grown at the lowest pulling rate. A detailed Raman analysis demonstrated that the global content of Fe2+ increases with pulling rate, while the growth under a lower pulling rate promotes the α-Fe2O3 crystallization. Atomic/magnetic force microscopy provided further evidence of phase-separated iron oxide crystallites formation with a high Fe2+/Ftotal ratio as the pulling rate increases. The magnetic measurements performed over a wide temperature range showed that the highest magnetization is found in the fibre grown at the highest pulling rate. A strong correlation between structural-topographical features and the magnetic characteristics of the glass fibres is substantiated.publishe