Florin Tudorache

Temperature dependence of tunability of Ba(SnxTi1−x)O3 ceramics

The electric field dependence of the dielectric constant (dc-tunability) as a function of temperature for a few compositions of Ba(Sn,Ti)O3 ceramics was investigated. Dense and homogeneous BaSnxTi1−xO3 ceramics (ferroelectric for x = 0.05 and x = 0.10, relaxor for x = 0.15 and 0.20) with high dielectric constant and low dielectric losses were prepared by solid state reaction. Their dc-tunability characteristics were investigated at a few temperatures from 20–120 °C, including the Curie range. The tunability data were discussed in terms of the Johnson model completed with a Langevin term that describes the “extrinsic” contribution to the nonlinear ɛ(E) dependences.

Humidity sensor characteristics and electrical properties of Ni–Zn–Dy ferrite material prepared using different chelating-fuel agents

Abstract Humidity sensor characteristics and electrical properties of Ni–Zn ferrite material doped with Dy were studied after synthesis via sol–gel self-combustion method. In order to obtain different micro configurations of the material reflected in different porosities, four different fuel agents were involved: citric acid, tartaric acid, cellulose and urea. XRD and XPS techniques were used to certify the composition. The influence of fuel agent and structural features on the electrical properties of ferrite sintered pellets was investigated at room temperature as a function of frequency and humidity. Because the electrical characteristics of a porous material can significantly affect by the humidity, the electrical measurements were carried out in controlled humidity environments. Conduction mechanism is explained in terms of fuel agent influence on phase composition, grain size value, cation distribution and induced strain within spinel lattice by dissolution of voluminous Dy3+ ions. The humidity sensors applicative characteristics of the material are highlight by analyzing the sensitivity, response and recovery times of nickel–zinc–dysprosium ferrite used as active material.

Synthesis and Characterization of Co-Substituted Ferrite Nanocomposites

We report the synthesis of CoxNi1-xFe2O4 (where x is 0, 0.25, 0.50, 0.75, 1) nanoparticles (NPs) by a wet chemical method using carboxymethyl cellulose (CMC) solution as surfactant. Their structure and magnetic properties were evaluated by X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The gas and humidity sensing properties of the samples were also investigated. Powder X-ray diffraction analysis demonstrated the formation of face-centered cubic structure for all the samples. The average crystallite size and lattice parameters have been calculated by Rietveld refinement. The FTIR spectra of NPs confirm the presence of CMC functional groups and stretching bands attributed to the intrinsic vibrations of tetrahedral and octahedral sites of spinel ferrite. The magnetization curves of the nanocomposites at room temperature demonstrated saturation magnetizations from 21 emu/g to 58 emu/g and coercivity values between 130 Oe and 835 Oe. As not many studies have been published on this topic, the gas sensing properties of Ni-substituted Co ferrites have been evaluated. The measurements revealed that Co0.25Ni0.75Fe2O4 is the most sensitive to acetone vapors.

Combined effects of p–n heterojunctions and active surface areas in a composite material dedicated to gas sensing applications

In this study, we analyze the unexplored field of combined effects of active surface area and p–n heterojunctions of a composite material dedicated to gas sensing applications. The used materials are thin films of mixtures of copper and zinc oxides. Individually, both copper oxide and zinc oxide shows interesting sensing performances toward a broad category of gases. The investigated films are obtained by thermal oxidation of Cu/Zn metallic multilayers. Cu/Zn metallic multilayers were obtained by using physical vapor deposition technique. The sensitivity of the composite materials, at ethanol, LPG and CO respectively, was investigated and it was observed that the highest sensitivity is obtained for ethanol. Complementary investigations (X-ray Diffraction, X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy respectively) were conducted in order to understand, explain and confirm the relationship between the oxidation conditions, structure, surface morphology and the exhibit sensing properties. The experimental results indicate that the sensitivity depend on the oxidation duration.