Search

In the present work, we aim to analyze the magnetocaloric and electrical properties of (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 manganite prepared by solid-state method at high temperature. The experimental results of the magnetization show that the (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 compound exhibits a paramagnetic–ferromagnetic transition at TC = 240 K. In addition to the experimental study, theoretical approaches are adopted to investigate the magnetocaloric behavior of this sample. The important parameters such as maximum entropy change, full width at half maximum (δTFWHM) and relative cooling power are explained qualitatively. The electrical properties of the studied sample have been investigated by using a complex impedance spectroscopy technique. These electrical measurements reveal that (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 sample exhibits a metallic behavior at low temperature and insulator one at high temperature. The temperature (TMI) of the metal–insulator transition is found to be about 240 K. The effects of frequency, temperature and composition on permittivity e′, e″ and dielectric loss (tanδ) have been also discussed in terms of hopping of charge carriers between Mn3+ and Mn4+ ions.

The new perovskite compound La0.62Eu0.05Ba0.33Mn0.85Fe0.15O3 was successfully synthesized via the sol–gel process. X-ray diffraction revealed that our sample is pure and crystallizes in the orthorhombic structure with Pbnm space group. Electrical properties were performed using the complex impedance spectroscopy technique in the range of frequency (40–10 MHz) and at various temperatures (80–400 K). AC-conductivity results are well described by the universal Jonsher’s power law at low temperatures and the DC-conductivity data are well fitted by the small polaron hopping model at high temperatures. Impedance results show a negative temperature coefficient of resistance (NTCR) which discloses the semiconductor behaviour of the studied sample. Nyquist plots were well fitted by an equivalent circuit involving the contribution of grain and grain boundaries in the conduction process. Giant dielectric values, useful in electronic devices, were obtained. Moreover, a relaxation diffuse phase transition is attributed to a strong heterogeneity in A and B sites of the studied perovskite.

A new organic–inorganic hybrid centrosymmetric compound, (C4H12NO3)CdCl3·H2O, was synthesized by the slow evaporation method at room temperature and characterized by single X-ray diffraction (SCXRD). The results of the X-ray diffraction study demonstrated that this material crystallizes in the triclinic system with the space group P 1 ¯ and the following unit cell parameters a = 6.822(6) A, b = 8.96(2) A, c = 10.034(3) A, α = 72.901(3)°, β = 71.927(3)°, γ = 89.099(3)° and Z = 2. In the crystal structure, the atomic arrangement is described as an alternation of organic and inorganic layers along the a-axis. The anionic layers are formed by [CdCl5O]− octahedrons, while the cationic layers are made up of [C4H12NO3]+ cations. The crystal packing is governed by N H⋯Cl, N H⋯O, C H⋯Cl, O H⋯Cl and O H⋯O hydrogen bonds, forming a three dimensional supramolecular network. Hirshfeld surfaces and 2D fingerprint plots were determined for visualizing, exploring and quantifying the intermolecular interactions in the crystal lattice of the title compound. Infrared and Raman spectroscopy were reported at room temperature in the frequency domains 400–4000 cm−1 and 50–500 cm−1, respectively. Differential scanning calorimetry (DSC) revealed one exothermic peak located at around T1 = 368 K. Electrical and dielectric properties were investigated as a function of temperature (300–430 K) in the frequency range 40 Hz–110 MHz. The electrical and dielectric studies were performed by means of impedance spectroscopy and dielectric permittivity e ' , e ' ' . Nyquist curves were well fitted to an equivalent circuit formed by parallel combination resistance and capacity fractal of the bulk. The frequency dependence of the alternative current (AC) conductivity was analyzed using the Jonscher law. Overlapping-large polaron tunneling (OLPT) and non-overlapping small polaron tunneling (NSPT) conduction mechanism models successfully explained the behavior of the exponent n.

In this study, an intrinsic hydrogenated amorphous silicon (a-Si:H) thin film was deposited using the plasma-enhanced chemical vapor deposition technique. The samples were annealed at 700 °C and 900 °C for 1 h. Optical measurements indicated the formation of nanocrystallites embedded in an amorphous a-Si:H matrix and the density increased with the annealing temperature. The electrical properties of the Schottky diodes Au/a-Si:H were investigated using admittance spectroscopy over a temperature range of 300–500 K. The conductivity at room temperature in the dark increased by several orders of magnitude after the transition from an amorphous to nanocrystalline structure. The activation energy was deduced based on the variations in the conductivity with temperature. The responses of the amorphous and nanocrystalline phases were identified by complex impedance analysis. The amorphous phase was dominant at low frequencies and high temperatures, whereas the response of the nanocrystalline phase was observed at high frequencies and low temperatures. Semicircular arcs were observed in the impedance plot at different temperatures and an electrical equivalent circuit was proposed. Complex impedance analysis demonstrated that the relaxation phenomenon was a thermally activated process. Moreover, we deduced the temperature at which the available density of the trapped charge states vanished based on the temperature dependence of the average normalized change.

The effect of nickel doping on the morphological and electrical properties of La0.67Ba0.33Mn1-xNixO3 (x = 0 and 0.075) manganite prepared by sol-gel process was undertaken. The morphology and grain size of these samples were carried out using scanning electron microscopy (SEM). Our samples have a homogeneous and porous morphology. The average grain size decreases from 130 nm (for x = 0) to 110 nm (for x = 0.075). Electrical measurements were investigated using conductance spectroscopy technique in 102–106 Hz and 80–320 K, frequency and temperature ranges, respectively. AC and DC conductance analysis indicate that both compounds exhibit a metal-semiconductor transition at TMS, which decreases from 240 to 220 K with Ni doping. From DC conductance study, conduction mechanism is found to be dominated by the small polaron hopping process at high temperature. Activation energy is deduced from the variation of conductance with temperature. This energy increases from 34 meV for x = 0–70 meV for x = 0.075. This behavior can be related to the reduction of the density of charge carriers with nickel concentration. The variation of the conductance with frequency follows Drude model.

This work investigates the metal induced crystallization of hydrogenated amorphous Silicon (a-Si:H) thin films, processed by plasma enhanced chemical vapor deposition, using Au nanoparticles (AuNPs) as crystallizing mediator metal. Electrophoresis deposition (EPD) of colloidal AuNPs was used to coat the Si substrates before the a-Si:H processing. Then, the crystallization was conducted by isothermal annealing for temperatures above the eutectic (500 and 600 °C). Raman spectroscopy analysis showed that the crystalline volume fraction doubled as the EPD time increases. Scanning electronic microscopy and energy-dispersive X-ray microanalysis revealed that AuNPs induced crystallization at 600 °C was achieved through eutectic reaction with mixing layers. Structural characterizations showed that the low amounts of AuNPs exhibited a metal mediating effect more pronounced than that of continuous Au thin film deposited by dry physical methods. The enhancing effect of AuNPs was assigned to their size dependent high surface energy. Herein, we discuss as well, the effect of the EPD time on the development of Si crystallites on the basis of thermodynamic and kinetic considerations.

La0.6Ga0.4Fe1-x MnxO3 compounds (x = 0, 0.1, 0.2 and 0.3) have been prepared using solid state reaction route. Structural, optical and electrical properties of the elaborated samples have been investigated in order to establish the effect of doping by manganese. The X-ray diffraction study implies that replacing Fe with Mn forces no phase transition. They have an orthorhombic structure with different sizes of crystallites. Optical measurements prove that the optical band gap Eg increases from 2.72 eV to 3.25 eV when increasing the manganese content. Also, electrical characterization shows that the conductivity is dependent on Mn concentration. Conduction process is found to be thermally activated. Then, small polaron hopping is the appropriate conduction mechanism. The temperature dependence of the exponent “n” indicates that the CBH model governs the conductivity over dispersive region. Impedance response of undoped sample is found to be different from the doped ones. But, for all investigated samples, grain boundary is more resistive than grain. The inferred activation energy (Ea) from the conductivity, the relaxation time and the grain boundaries are closed to each other. Also, it si found that Ea values vary similarly as a function of manganese content.

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.

In this work, we report on vapor–liquid–solid growth of silicon nanowires (SiNWs) catalyzed by indium, a low-eutectic post-transition metal. The indium catalyst is synthesized ex situ by annealing indium-coated substrates using two different annealing processes: rapid thermal annealing (RTA) and conventional process. The effect of annealing parameters on indium catalyst properties is studied. We show that after conventional annealing at 600 °C during 45 min, the indium layer is cracked into elongated and inhomogeneous islands of different sizes. X-ray diffraction (XRD) analysis depicts in addition to pure indium planes the presence of new peaks attributed to indium oxide planes formed during annealing. While by using RTA process, oxide-free indium particles were successfully grown in one step by during short time (5 min) at 400 and 450 °C. Quasi-spherical and homogeneously distributed indium particles were obtained at 450 °C. A comparative study between SiNWs catalyzed by indium catalyst prepared following the two different processes was carried out. The indium oxide presence negatively affected the catalytic property of indium, resulting in a lower density of the grown SiNWs. An improvement of the SiNWs density was achieved with RTA-annealed catalyst, as more indium particles were present to act as active catalyst to the growth. The catalyst annealing conditions also affected the size of the SiNWs, with shorter wires with RTA process. However, the shape of the SiNWs was similar in both studied cases, where the wires were bent and kinked. The morphology investigation of the SiNWs also shows that the SiNWs have a core–shell structures consisting of amorphous and crystalline silicon.

The polycrystalline sample BaTi0.5 (Co0.33 Mo0.17) O3 was synthesized by the sol-gel method. The effect of replacing titanium by cobalt and molybdenum on the structural and electrical properties of our compound was investigated. The results of X-ray diffraction (XRD) at room temperature showed a pure tetragonal perovskite. The electrical response was studied by complex impedance spectroscopy over a broad frequency range (30–106 Hz) at different temperatures. The values of ac conductivity were fitted by Jonscher's law σ(ω) = = σ DC + Aω n and supported by the correlated barrier hopping (CBH) mechanism. Complex impedance analysis confirmed the existence of an electrical relaxation in the compound. The dielectric constant and the dielectric loss decreased with the increase in frequency. This behavior can be explained by the presence of the Maxwell–Wagner type of polarization responsible for the electric conduction. The modulus plots were characterized by the Havriliak–Negami (H-N) and the empirical Kohlrausch–Williams–Watts (K.W.W.) functions. The Normalized plot of the imaginary part of modulus indicates that the dynamical processes are temperature independent.

Hydrogenated silicon (Si:H) layers have been deposited on crystalline silicon substrate by radiofrequency plasma-enhanced chemical vapor deposition technique (rf-PECVD) from SiH4/H2 gas mixture using different deposition times and after a seed layer with thickness of 70 nm (to improve the nucleation of nanocrystallites). The effect of the deposition time on the as-deposited and annealed layers was investigated. Ultraviolet–visible–infrared (UV–Vis–IR) spectroscopy was used to determine the thickness of the layers. Before annealing, the layer thickness showed a linear variation with deposition time in the range from 450 s to 1500 s. On the other hand, for deposition times of 450 s, 600 s, and 1500 s, the layers showed an x-ray diffraction (XRD) peak corresponding to the (111) crystal plane of Si. Raman spectroscopy confirmed the appearance of the crystalline phase in these layers. Raman scattering studies showed that, when using the short deposition time for the top layer, the crystalline peak dominated. We deduce that insertion of a seed layer improves the crystallinity of the top layer. In addition, the crystallinity increased slightly with the deposition time. The structural properties of the layers annealed at 900°C were studied by Raman spectroscopy and XRD analysis. We noted an increase in the crystalline volume fraction and the appearance of (111) crystal plane of silicon, confirming the transition from amorphous to nanocrystalline phase for all the annealed films.

A detailed investigation of structural, electrical and dielectric properties of Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 manganite prepared by the sol-gel method was undertaken. The Rietveld refinement of X-ray diffraction pattern reveals that this compound is indexed in the orthorhombic structure with Pbnm space group. Structural properties are also analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy at room temperature. DC conductivity (σDC) data show the presence of a semiconductor-metal transition at TSM = 360 K. σDC is described by small polaron hopping model at high temperatures and variable range hopping model at low temperatures. AC conductivity results follow the universal Jonsher's power law at relatively low temperatures and Drude's model at high temperatures. The impedance plots display the contribution of both intra- and inter-granular contributions. Dielectric measurements exhibit highly remarkable dielectric permittivities useful in electronic devices. Dielectric losses are shown to be governed by the DC conduction mechanism and described by the Giuntini theory.

Bi1-xNdxMn2O5 with (x = 0, 0.1 and 0.2) samples prepared by sol gel method, have been investigated for its structural and dielectrics properties. 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. Scanning electron microscopy (SEM) revealed that the grains are irregularly spherical-like shaped confirmed the formation of single-phase materials with excellent mapping distribution, with mean sizes of 107 , 103 and 92 for (x = 0, 0.1 and 0.2) respectively. The Dc conductivity expresses a semi-conductor dependence on temperature for the three samples all over the explored range of temperature. In addition to that, the substitution of Bi by Nd enhances the conductivity. The evolution of Dc conductivity versus temperature obeys to Mott and Davis law, which proves that the thermally activated small polaron hopping is the appropriate model of conduction at high temperature. Then it switches to variable range hopping at low temperature for BiMn2O5 and Bi0.9Nd0.1Mn2O5. The Ac conductivity is governed by the Jonsher law and its analysis shows that the correlated barrier hopping is the appropriate model of conduction for the two doped samples (Bi0.9Nd0.1Mn2O5 and Bi0.8Nd0.2Mn2O5) while the overlapping large polaron tunneling is the suitable model for the undoped one. The impedance analysis is in good coherence with the conductivity analysis and emphasizes the undoubtedly contribution of grain boundaries in the transfer properties. Dielectric analysis allows to notice the heavy increase of e ’ with the increase of the mount of Nd. Besides, the evolution of e ’ with temperature suggest a relaxor behavior and is distinguished by the occurrence of peaks attributed to the existence of polar nanoregions.

Perovskite ceramics [Ba0.8Sr0.2]1−x[Bi1−yYy]xTi1−xFexO3 with x = 0.3 and 0.05

The hybrid compound Dimethylammonium zincochloride [(CH3)2NH2]2ZnCl4 is synthesized using a slow evaporation method at room temperature. It crystallizes in the monoclinic system with the P21/n space group. The differential scanning calorimetric shows one phase transition at 444 K. In optical studies, the analysis of the data revealed the existence of optical direct allowed transition mechanisms with the band gap energy equal to 4.26 eV. The ac electrical conductivity is investigated at the frequency and temperature range of 1 Hz–1 MHz and of 415 K–451 K respectively. The presence of the grain interior and grain boundary contributions to the electrical response in the material is clearly manifested in both of the two semicircles observed in the complex impedance. The equivalent circuit based on the Z-View-software is proposed and the conduction mechanisms are determined. Dielectric data are analyzed using complex electrical modulus M* at various temperatures.

The effect of substituting sodium by potassium on electrical and dielectric properties is investigated in details for the GdFeO3-type Pr0.8Na0.2-xKxMnO3 (x = 0.00, 0.05, 0.1, 0.15 and 0.2) manganites. The electrical measurements indicate that the parent compound exhibits a metal behavior. When introducing potassium, all samples show a metal–semiconductor transition. Then, the increase of K content reduces the resistivity in the whole temperature range but doesn’t affect the metal–semiconductor temperature transition (TMS). At a specific temperature TS, a saturation region was marked in the resistivity curve. It is found that TS values shift toward lower temperatures when the potassium content rises. The TS value approaches to room temperature for x = 0.2. The temperature coefficient of resistance (TCR) of the investigated manganites shows significant value, especially for x = 0, indicating that these ceramics can be used for a specific application such as bolometer technology. The frequency dependence of conductance was investigated through Jonscher's universal power law and the electrical conduction mechanism well interpreted by the correlated barrier hopping (CBH) model. Impedance spectroscopy measurements indicate that the electrical behavior of these perovskites is primarily dominated by the grain boundary response. The dependence of the dielectric constant on the frequency and the temperature confirms that the investigated samples are of a classical dielectric type.

Orthoferrites perovskites are an important family of materials in the field of nanotechnology, particularly for cathodes in solid oxide fuel cells. Doping these materials enables the enhancement and control of their properties. In this context, we studied the effect of Ti doping on different properties of the La0.7Ga0.3Fe1-xTixO3 (x = 0, 0.1, 0.2 and 0.3) lanthanum orthoferrites. X-Ray Diffraction (XRD) measurements proved the presence of two orthorhombic phases with Pbnm and Pnma space groups. SEM images corroborate the XRD results, clearly signaling the presence of two phases in these samples, with EDS analysis allowing the estimation of each phase fraction. FTIR and Raman spectroscopies allowed us to study the vibrational modes related with the La-O, Fe-O and Ti-O bonds. We note a shift towards higher wavenumber associated with the increase in Ti. Magnetic measurements showed a transition from antiferromagnetism to weak ferromagnetism with the introduction of Ti. The zero-field cooled (ZFC) and field cooled (FC) magnetization versus temperature curves do not superimpose, proving the heterogeneity of the magnetic properties of the samples. The saturation magnetization Ms, the remanent magnetization Mr and the coercive field Hc decrease with both increasing temperature and Ti content.

The topotactic reduction of La0.75Ba0.10Sr0.15FeO2.875 with titanium metal leads to a new isostructural material of the composition La0.75Ba0.10Sr0.15FeO2.875−δ (δ = 0.375 and 0.50). XRD analysis of phases confirms that the obtained compound adopts a brownmillerite-type structure. A slight distorted monoclinic P2/m was found to describe the crystal structure. The transport properties have been investigated by current–voltage (I–V). The electric and dielectric measurements were carried out covering a wide range of temperature (300–600 K). Our materials display semiconducting properties as well as mixed ionic and electronic conductivity. At high temperatures, the activation energy values proved to be around 907 − 630 meV, which refers basically to oxygen vacancies conduction. The analysis of dielectric properties and dielectric losses (ε’, tanδ) of both compounds vs temperature at different frequencies demonstrates two relaxer attitudes. A low dielectric loss and low electrical conductance were displayed. Relying upon these values, these materials stand for perfect candidates for micro-electronics devices.

The CuFeCr0.5Ni0.5O4 (CFO) compound was synthesized using sol-gel reaction combustion technic. The structural analysis showed that the obtained composites have a polycrystalline nature and the cubic spinel structure ( space group). Microstructural analysis revealed the formation of spherical and elongated grains of our sample. The dielectric and electrical transport properties of CuFeCr0.5Ni0.5O4 were investigated in detail by Ac impedance spectroscopy in a wide range of temperature (200 K-400 K) and frequency (100Hz to100KHz). Our results show that the electrical modulus and impedance studies confirm the presence of a relaxation phenomenon with non-Debye type in the prepared sample. The activation energy Edc estimated from the slope of the linear fit plot is equal to 0.158 eV with frequency of 100Hz and 0.126 eV with frequency of 1MHz at temperature range 200K-400K. Close activation energies values were found from analyzes of relaxation time and dc-conductivity indicating that the relaxation and the conduction processes may be attributed to the presence of free carrier charges and impurities at the grain boundaries. The conduction process for samples is described by the NSPT model. The complex impedance analyses and modulus formalism confirm a grain and grain boundary mechanism contributing to the dielectric properties. The real and the imaginary parts of the impedance are well fitted to equivalent electrical circuit (Rg+ Rgb//CPEgb) was used for modeling the Nyquist data.

The alkylammonium halogenoferrate families are subjected to diverse studies according to their wide field application. However, these compounds show various transitions depending on the preparation process. In this paper, the [(C

This work deals with the physical investigations on Zn-doped TiO2 synthesized via a solvent controlled non-aqueous sol–gel route. X-ray diffraction analysis indicated that TiO2 particles crystallized in both tetragonal anatase and rutile structures. FTIR analysis confirmed the insertion of Zn in TiO2 network, and revealed the presence of surface defects in the prepared powders, as proved by their porous morphologies. UV-visible absorption was performed to provide an insight into the band-gap variation in the Zn-doped TiO2 nanopowders as a function of Zn doping. On the other hand, the electrical properties were studied using complex impedance spectroscopy in the frequency range from 40Hz to 1MHz at temperature range 480-600K. The impedance plots are well fitted to an (R1//C1)-(R2//CPE1) equivalent circuit. As well, the correlated barrier hopping model (CBH) was proposed to describe the conduction mechanism. Finally, Photocatalytic activities of the Zn doped TiO2 nanoparticles were evaluated via the degradation of the rhodamine B (RhB) dye under UV light irradiation. The results showed enhanced performance by Zn-doping, compared to the undoped TiO2 nanoparticles.

Passivation of interface states in the Schottky barrier is an approach to enhance the properties of the Schottky devices. In this work, Au/0.8nm-GaN/n-GaAs Schottky structure is studied electrically in a wide temperature range. With increasing temperature, the reverse current Iinv increases from 1×10-7 A to 1×10-5 A, and the saturation current Is increases from 1×10-32 A to 5×10-7A. The series resistance Rs decreases with increasing temperature from 13.44 Ω to 4.25 Ω. The ideality factor n decreases from 10.64 to 1.15. The barrier height increases abnormally with increasing temperature from 0.54 eV at 80 K to 1.03 eV at 180 K, then decreases to 0.82 eV at 420 K. The abnormal behavior of and the high values of n in low temperature are due to the tunnel mechanisms effects, such as FE and TFE currents. FE mechanism is the dominant process at low temperatures (80-300 K) and TFE mechanism is the dominant one at high temperatures (300-420K). Finally, our structure presents an inhomogeneous barrier height, maybe caused by the thin GaN interface layer.

We have prepared a 20% Pr doped Sm0.55Sr0.45MnO3 sample by using the solid-state reaction and studied the magnetic and electrical properties. Arrott plots confirm the occurrence of a first-order phase transition. All the signatures of the FM first-order transition disappear above a critical magnetic field. Based on dc-electrical conductivity, a metal semi-conductor transition has been observed at TM-Sc = 180 K. Temperature-dependent conductivity measurement has been carried out to probe the electrical conduction mechanism, which revealed the change of conduction mechanism from the variable range hopping to the small polaron hopping around 180 K. The temperature dependence of e’ indicates a dielectric anomaly, implying a possible ME coupling in the vicinity of FM transition. The modulus spectra and complex impedance of the reported sample undoubtedly showed the non-Debye type relaxation process. We have obtained different activation energies values calculated from the conduction and relaxation mechanism. An electrical equivalent circuit model was suggested to explain the impedance contributions.

In this paper, a new model of thermionic emission current for non-ideal Schottky contacts and a method of extracting electrical parameters are presented. The Au/n-GaAs Schottky structure is fabricated and simulated using Silvaco–Atlas software in a wide temperature range. The proposed method shows series resistance $$ R_{s} $$ values close to those obtained from ln(I)–V method and ideality factor n in good agreement with the reported experimental studies. The barrier height $$ \phi_{b} $$ extracted by our method is in good agreement with those extracted from the band diagram (BD) and capacitance–voltage (C–V) characteristics. It is increased with decreasing temperature, in accordance with the band gap variation with temperature and the reported negative temperature coefficient of the barrier height. Conversely, $$ \phi_{b} $$ obtained from the classical model using ln(I)–V method shows an abnormal behavior and discordance with the $$ \phi_{b} $$ extracted from the band diagram and C–V characteristics. Finally, the proposed model shows identical characteristics with the simulation and the experimental curves, in all temperature range, while the classic model shows large deviations at high bias voltages.

We investigated the effect of iron substitutions upon the structural, magnetic, electric, and dielectric properties in Pr0.7Ca0.3Mn1–xFexO3 mixed-valence manganite. The samples were synthesized using the solid-state reaction method and were analyzed by X-ray diffraction, magnetic and impedance spectroscopy measurements. X-ray diffraction analysis shows that all samples were found to be single phase and crystallize in the orthorhombic structure with Pnma space group. While the parent compound Pr0.7Ca0.3MnO3 exhibits a charge order sate, the substituted samples with low amount of iron exhibit a paramagnetic to ferromagnetic transition. However, the Curie temperature TC decreases with Fe content when we move from x = 0.02 to x = 0.1. From DC-conductance measurements, a typical semi-conducting behavior without any transition is observed for all investigated samples. Beyond a certain critical temperature noticed Tsat, the DC-conductance begins to saturate and reaches a maximum value. Then, the saturation temperature increases with increasing Fe content to attain Tsat = 260 K for x = 0.10. The correlated barrier hopping model was used to explain the frequency dependence of AC conductance. Impedance measurements confirm the contribution of the resistive grain boundary on the conduction mechanism. Then, it proves the existence of multiple electrical relaxation phenomena in the studied samples. The dielectric constant is found to be temperature dependent indicating that the compounds are polar dielectrics where the dipole orientation is governed by increasing temperature.

In this study, a Cu

Pr0.65Ca0.25Cd0.1MnO3 ceramic was elaborated using the conventional solid-state reaction technique. The polycrystalline sample was subjected to investigate by ac impedance spectroscopy. From the main results, the electrical conductivity analysis confirms the semiconductor behavior and indicates that the hopping process governs the electrical conductivity. From ac-conductivity, two distinct mechanisms are observed. Indeed, the conduction mechanism is attributed to the correlated barrier hopping model in the middle of the frequency region and the overlapping large polaron tunneling in the high-frequency one. The analyzed impedance and modulus confirmed the presence of non-Debye-type relaxation phenomenon. Different electrical equivalent circuits were used to analyze the Nyquist plots. The obtained results confirm the contribution of grain boundary on the conduction. The increase in dielectric constant and the rate of its increase at low frequency were related to the disorder of the cation sublattices.

The chemical co-precipitation process was used for the synthesis of Fe-doped ZnO nanopowders (ZnO:Fe) with varying doping concentrations from 0% to 10 %. Doping with iron caused significant alterations in the physical properties of ZnO nanopowders. The XRD analysis revealed that Fe introduction forms a secondary phase of spinel ZnFe2O4 for doping concentration higher than 1%. The average crystallite size was proven to decrease with the increase in Fe concentration. SEM images showed the formation of spherical nanoparticles, where the average grain size decreased with doping. The Fe incorporation into the ZnO host lattice was also confirmed by FTIR and Raman spectroscopy. The optical properties were strongly influenced by Fe doping. The dielectric parameters were subsequently investigated as a function of frequency and composition. The observed dielectric dispersion was interpreted on the basis of Maxwell-Wagner interfacial model and Koops phenomenological theory. Overall, Fe doping improved the electrical conductivity of ZnO nanopowders.

Impedance spectroscopy technique was used to characterize the electrical properties in a wide range of frequency [40–105 Hz] and temperature [80–700 K]. As a result, AC-conductivity spectrum follows the ‘double Jonscher Power Law’ in the temperature range [80–280 K], ‘Jonscher Power Law’ in [300–600 K] range and at 700 Kit is described by the classical Drude model. Moreover, the AC-conductivity analysis reveals the contribution of multiple mechanisms in conduction. In fact, the variation of the frequency exponent ‘s1’ with temperature shows that the correlated barrier hopping mechanism is the dominated model for conduction of charge carriers beyond T = 470 K. The previous model was observed again according to the temperature dependence of the frequency exponent ‘s2.’ Then, the deduced activation energy decreases with increasing frequency suggesting the availability of hopping conduction. The temperature dependence of AC-conductivity proves the existence of metal semi-conductor transition at 200 K. At high temperatures, the DC-conductivity analysis reveals that the conduction process is dominated by thermally activated hopping of small polaron. However, at low temperatures, it is confirmed that the most suitable mechanism for conduction is the Shklovskii–Efros-Variable Range Hopping process.

Electrical properties of Pr0.7Ca0.3Mn0.9X0.1O3 (X = Co, Ni, Cr and Fe) systems have been investigated using impedance spectroscopy measurements. The reported results confirmed the role of cationic disorder on the transport properties of the doped Pr0.7Ca0.3MnO3 system. For the case of the substitution by Co and Ni and Fe transition metals, the lower temperature side has been marked by the activation of the hopping conductivity over the nearest sites. Moreover, the Shklovskii–Efros-variable range hopping conductivity mechanism has been observed in the case of the substitution by Cr element. In the high temperature range, the evolution of the resistance with temperature confirmed the activation of a hopping process. In such a temperature range, the conduction process of all the studied compounds is dominated by a thermally activated small polaron hopping mechanism. For the Pr0.7Ca0.3Mn0.9Cr0.1O3 compound, AC studies have confirmed that the electrical conductance should be investigated in terms of an activated quantum mechanical tunneling process. At higher frequencies, the Pr0.7Ca0.3Mn0.9Fe0.1O3 compound is characterized by the existence of a high frequency plateau. For the Pr0.7Ca0.3Mn0.9Fe0.1O3 ceramic, the dispersive region of the spectrum has confirmed the activation of the correlated barrier hopping mechanism. Thus, the conductance is found to follow the double Jonscher power law only for the temperature range of [80 K, 200 K]. For the Pr0.7Ca0.3Mn0.9Ni0.1O3 compound, the evolution of the frequency exponent has confirmed the activation of two conduction mechanisms. The non small polaron tunneling mechanism was activated at lower temperatures. Accordingly, the activation of the correlated barrier hopping mechanism was detected for the high temperature range. For Pr0.7Ca0.3Mn0.9Co0.1O3 manganite, the coexistence of two conduction mechanisms (correlated barrier hopping and the non small polaron tunneling) is noticed. The latter's were activated in the whole of the explored temperature range. Using the scaling model, the spectra of both Pr0.7Ca0.3Mn0.9Cr0.1O3 and Pr0.7Ca0.3Mn0.9Ni0.1O3 compounds merge into a single master curve, which confirms the validity of the time temperature superposition principle.

Ni0.5Zn0.5Fe2O4 was prepared by the solid state reaction route at different temperatures. The dielectric properties of spinel ferrites were investigated in the frequency range 50 Hz–10 MHz and in the temperature range 300–420 K. Conductance is shown to increase with increasing frequency and temperature. Impedance analyses indicated that the relaxation phenomenon is strongly dependent on temperature and frequency. The impedance plots displayed both intra- and inter-granular contributions. Electrical equivalent circuit was proposed to explain the impedance results. The decrease of giant permittivity values with the increase in frequency proves the dispersion in the low frequency range and is showing the Maxwell–Wagner interfacial polarization.

In the present study, the structural, morphological, electrical, and dielectric properties of Ni0.6Zn0.4Fe1.5Al0.5O4 annealed at 600 °C, 900 °C, and 1200 °C were investigated. The X-ray diffraction patterns confirmed the presence of the single-phase cubic spinel structure with the Fdm space group. The SEM images of Ni0.6Zn0.4Fe1.5Al0.5O4 nanoparticles demonstrated that these samples (Ni900 and Ni1200) were nano-sized and that the increase in annealing temperature enhanced the agglomeration rate. It was found that the electrical conductivity of the system improved on increasing the temperature over the whole explored range for the two low annealing temperatures, while this improvement declined after 500 K in the case of the highest annealing temperature. For such a sample, a metallic behavior was seen. The sample annealed at 1200 °C possessed the highest conductivity and the lowest activation energy. The impedance measurements were in good agreement with the conductivity plots and confirmed the emergence of a grain boundary effect with the increase in annealing temperature. For the sample annealed at the highest temperature, Z′ decreased rapidly with frequency. This sample exhibited the lowest defect density than the other samples. Consequently, its electrical conductivity increased. A Nyquist diagram was used to examine the contribution of the grains and grain boundary to conduction and to model each sample by an equivalent electrical circuit. The dielectric behavior of the investigated samples was correlated to the polarization effect.

The orthorhombic Pr0.8Na0.2MnO3 ceramic was prepared in polycrystalline form by a Pechini sol–gel method and its structural, magnetic, electrical and dielectric properties were investigated experimentally. A structural study confirms that the sample is single phase. Magnetic measurements show that the sample is a charge ordered manganite. The sample undergoes two successive magnetic phase transitions with the variation of temperature: a charge ordering transition occurred at TCO = 212 K followed by a paramagnetic (PM) to ferromagnetic (FM) transition around TC = 115 K. From an electrical point of view, a saturation region was marked in the conductivity as a function of temperature σ(T) curves at a specific temperature. The dc-conductivity (σdc) reaches a maximum value at 240 K. The obtained results are in good agreement with the temperature dependence of the average normalized change (ANC). We found that the conduction mechanism was governed by small polaron hopping (SPH) in the high temperature region and by variable range hopping (VRH) in the low temperature region. Complex impedance analysis indicates the presence of a non-Debye relaxation phenomenon in the system. Also, the compound was modeled by an electrical equivalent circuit. Then, the contribution of the grain boundary in the transport properties was confirmed.

Nanoparticles of Li0.5ZnFe1.5O4 (LiZn2Fe3O8) with the spinel structure were prepared by a sol–gel auto-combustion method at two different annealing temperatures. X-ray diffractograms and Rietveld refinement confirmed the formation of the spinel structure. The morphology was analyzed by electron microscopy, which showed that the grains were composed of different crystallites. Elastic properties were determined from infrared spectroscopy. It was found that the elastic parameters increased with the increase in annealing temperatures. The band gap depends on the annealing temperature and it decreased on increasing the particle size. The conductivity of the specimen annealed at 500 °C followed either the Jonscher's model or Drude's model depending on the temperature range. This conductivity decreased when the annealing temperature was raised by 600 °C. AC conductivity was found to be controlled by the hopping model. A single relaxation phenomenon was evidenced for each sample from impedance analysis. The Nyquist diagram proved that the samples were simultaneously capacitive and resistive and also supported the presence of multiple relaxation times.

Silver doped indium sulphide thin films (In2S3:Ag) were deposited by spray pyrolysis technique on glass substrates at temperature 350 °C. The films were prepared by varying the Ag:In ratio from 0% to 8%. The effect of silver concentration on structural and optical properties of In2S3:Ag thin films have been studied in detail using X-ray diffraction (XRD) and ultra violet, visible and near infra red (UV–Vis–NIR) transmittance spectroscopy. The X-ray diffraction analysis showed that the prepared layers are polycrystalline and crystallize in a β-In2S3 cubic structure and the size of the crystallites varies between 16 and 20 nm. UV–Vis–NIR spectroscopy measurements revealed that the optical transmittance of the films exceeds 90% in the visible and near infrared region and also the direct band gap energy of the fabricated thin film samples increases with doping from 2.63 to 2.97 eV. The roughness values evaluated are almost constant for different doping concentration.

In the present work, the effects of temperature and frequency on the electrical transport properties of polycrystalline samples of Ba(1-x)Nd2x/3TiO3 (BNxT) (x = 0.00 and x = 0.04), prepared by molten-salt method, are discussed. X-Ray diffraction reveals that all the samples crystallize in a tetragonal symmetry (space group P4mm) with the formation of nanoparticles. The crystallite size was found to vary around 40 nm. DC-conductivity measurements show and that all samples are characterized by a semiconductor behavior. The frequency dependent behavior of conductivity was well fitted in Jonscher's universal power law and interpreted in terms of Overlapping Large Polaron Tunneling (OLPT) mechanism. The Cole-Cole plot analysis of impedance spectra enabled to distinguish two relaxation behaviors assigned to originate from grains and grain boundaries. Besides, it was found that the electrical behavior of the ceramics is dominated by the grain-boundary response. Furthermore, the frequency dependence of electric modulus was studied and explained using Kohlrausch-Williams-Watts (KWW) model and the normalized M ″ / M max ″ spectra of the samples suggest that the distribution of relaxation times is temperature dependent and originates by the same mechanism. In addition, the conductivity and electrical response behavior in all the samples can be attributed to the long-range movement of oxygen vacancies.

The solid-state reaction method was used to fabricate Pr0.65Ca0.25X0.1MnO3 manganite compounds with X = Cd, Sr, and Pb. X-ray diffraction (XRD), magnetometry, and impedance spectroscopy technique are used to study the structural, magnetic, electrical, and dielectric properties. The X-ray diffraction reveals that all samples crystallize in the orthorhombic system. The magnetic measurements on all samples show the presence of charge ordering transition at high temperature followed by an antiferromagnetic transition. From dc-conductivity analysis, all samples display the presence of semiconductor behavior. It is observed that the lowest obtained value of the activation energy (Ea) corresponds to the Pb-doped sample. The activation energy deduced from the dc-conductivity (Ea)σ matches very well with that estimated from relaxation time (Ea)relax, indicating that the relaxation process and the electrical conduction are related to the same origin. For each X dopant, the ac-conductivity is obeyed to the Jonsher law. The analysis of the impedance spectra highlights the presence of non-Debye relaxation phenomenon. Dielectric results show that the Pb doped sample has better dielectric properties than Cd and Sr doped ones. The dielectric properties are strongly dependent on both temperature and frequency. Dielectric constants decrease with frequency, and their behaviors have been interpreted based on space charge polarization according to Maxwell-Wagner’s two-layer model. The observed high conductivity and high dielectric permittivity values suggest that our compounds may be suitable for applications in electronic devices.

Sn2Sb2S5 materials were synthesized by thermal evaporation using earth-abundant tin, antimony and sulfur elements. The effect of annealing temperature on structural, morphological, optical, thermal and electrical characterization was obtained using many techniques. The deposited films were annealed in air for 1 h at 100 °C and 300 °C. X-ray diffraction analysis reveals that while as-deposited films are amorphous, a crystallized phase, with an orthorhombic crystalline structure, appears after annealing. Via the photothermal deflection spectroscopy, the sub-bandgap energy decreased from 1.98 to 1.75 eV with rising the annealing temperature. Besides, static and dynamic thermal properties of as deposited and annealed Sn2Sb2S5 thin films were measured using electropyroelectric method. It was observed that an increase (40.5–46.5 W m−1 K−1) was found for the thermal conductivity values by increasing annealing temperature, while thermal diffusivity decreases from 12.1 × 10−6 to 9.31 × 10−6 m2 s−1. Moreover, Nyquist spectra performance in the temperature range 300–540 K revealed the presence of a relaxation phenomenon in the microstructure of the studied sample. In addition, the level of the peaks is crashed with temperature, showing that the charge carriers are thermally activated. Finally, Sn2Sb2S5 thin film annealed at 300 °C was found the best sample for use in optoelectronic and solar cell devices. This work suggests a low cost promising compound for scalable synthesis of Sn2Sb2S5 thin films for solar cell and photovoltaic applications.

From the XRD results, it is found that the studied La0.5Ca0.2Ag0.3MnO3 compound crystallizes in the orthorhombic structure with Pnma space group. Electrical conductivity of La0.5Ca0.2Ag0.3MnO3 compound is investigated from 80 K to 480 K in the frequency range [40Hz-6×105Hz]. Several conduction models are used to identify the appropriate mechanisms governing the transport properties in the studied compound. The Overlapping-Large- Polaron Tunneling and the Correlated Barrier Hopping conduction processes are used to clarify the sub-linear dispersive regions in the DJPL/JPL frequency range. In these regions, the conductivity is examined according to double and single Jonscher power laws. At lower temperatures and for the second frequency range, the spectra reveal Superlinear Power-Law behavior. Beyond T=280 K, this phenomenon is disappeared and replaced by Nearly Constant Loss behavior. At higher frequencies, the conductivity spectra exhibit a high frequency plateau. For the DC regime, the transport properties are governed by thermally activated Small Polaron Hopping conduction process at elevated temperatures. The Variable Range Hopping conduction mechanism is the dominant process in the intermediate temperature range. Thus, the cationic disorder plays a major role in the transport of charge carriers at low temperatures. Likewise, the investigated compound exhibits semi-conductor behavior over the explored temperature region. The deduced hopping energy is sensitive to the frequency parameter. At high frequencies, a signature of a metal-semiconductor transition is observed at 260 K. The magnetic investigation shows that the sample reveals a paramagnetic-ferromagnetic phase transition at 260 K.

We prepared hydrogenated thick silicon film by plasma enhanced chemical vapor deposition (PECVD) method using SiH4 and H2 gas mixture and we investigated the effect of the hydrogen dilution ratio defined as $$ R=\frac{\left[{H}_2\right]}{\left[{SiH}_4\right]} $$ on the as-deposited and annealed films. With increase in hydrogen dilution ratio, amorphous to microcrystalline transition has been observed. The crystallization has been confirmed from Raman spectroscopy, UV reflectance, low angle X-ray diffraction (XRD), spectroscopic ellipsometry and atomic force microscopy (AFM) analysis. Tauc band gap shows a decreasing trend with increasing H2 dilution of silane. It decreases from 1.8 to 1.57 eV. It has been concluded that H2 dilution of silane in PECVD enhances the crystallinity of the film and affects its optical and structural properties.

Bi4-xYbxTi3O12 with x = 0.0, x = 0.1, x = 0.2 and x = 0.3 specimens were synthesized by conventional solid-state reaction. The influence of ytterbium doping on the structural, optical, dielectric and electrical properties of the synthesized compounds were investigated. The X-ray diffraction analysis showed that all samples are homogenous and crystallize in the orthorhombic system with the Fmmm space group. Also, it is found that the unit cell volume (V) goes on decreasing owing to the decrease of lattice parameters (a, b and c) with increasing Yb content. The absorbance measurement reveals that the intensity increases with increasing ytterbium concentrations. Also, it exhibits an additional peak occurred at the wavelength 975 nm. This peak has been attributed to the characteristic transitions from ground state 2F7/2 to excited states 2F5/2 of Yb3+ ions. From DC-resistivity measurements, it is noticed that all compositions exhibit a semiconductor behavior. In addition, it is found that below 420 K, the electrical resistivity was enhanced considerably upon substitution up to x = 0.3. Such behavior was attributed to the decrease of oxygen vacancies density. At 420 K, the parent compound exhibits a saturation region, which shifts to higher temperatures upon rising Yb content. The deduced activation energy values at high temperatures altercated around 990–828 meV. These values are attributed to oxygen vacancies migration. The electrical conductivity behavior of the samples was explained on the basis of jump relaxation model. As well the conductivity spectrum obeys to the Jonscher universal double power law.

Orthorhombic Pr0.8Sr0.2MnO3 sample is prepared by solid-state reaction method and quenched in water. The occurrence of a second-order phase transition is confirmed by Arrott plots. The critical exponents determined using different models are in good agreement with the 3D-Ising model. The magnetocaloric results have shown an important maximum of the magnetic entropy change and relative cooling power evaluated at 2.14 J kg−1 K−1 and 101.52 J kg−1 under a field change of 2T. The DC conductance measurements revealed that this compound exhibited a semiconductor to metallic behavior at T SM = 400 K. Moreover, the AC results are described by the Jonscher power law. Concerning the electrical and dielectric properties, they disclosed the behavior-dependency of both temperature and frequency. As for the complex impedance measurements, they showed that the conduction mechanism was governed by grain boundaries. The dielectric results demonstrated important values of the real part of the permittivity, and the Pr0.8Sr0.2MnO3 material can be used for capacitor manufacturing.

In this work, we report the effect of Ti-doping on the structural, electrical and dielectric properties of Pr0.75Bi0.05Sr0.1Ba0.1Mn1−xTixO3 (x = 0 and 0.04) manganites synthesized by sol–gel route. X-ray structural analysis using Rietveld refinement technique reveals that our samples are single phase and crystallize in the orthorhombic system with Pbnm space group. These structures were characterized by impedance spectroscopy in the frequency range from 40 to 1 MHz and temperatures between 80 and 400 K. DC conductivity analysis shows that our samples disclose a semiconductor behaviour with a semiconductor–metal transition temperature TMS at 380 and 360 K for x = 0 and 0.04 respectively. This result shows that the TMS temperature can be controlled by varying the titanium content. AC conductivity (σAC) results show a considerable sensitivity to both temperature and frequency. The impedance plots were well described by an equivalent circuit model taking into account the contributions of semiconductor grains and insulating grain boundaries in the conduction mechanism. Furthermore, a non-Debye type of relaxation in our compounds was confirmed. In addition, we have demonstrated that the dielectric relaxation is hidden by the DC conduction mechanism.

Polycrystalline samples of La0.67-xEuxBa0.33Mn0.85Fe0.15O3 (x = 0.0, 0.1) manganites have been prepared using sol-gel route. Structural characterizations of our materials were performed by powder X-ray diffraction, Scanning Electron Microscopy and by Energy Dispersive X-ray spectroscopy at room temperature. Our samples are single phase and crystallize in the orthorhombic structure with the Pbnm space group. Electrical and dielectric properties of La0.67-xEuxBa0.33Mn0.85Fe0.15O3 (x = 0.0, 0.1) compounds have been studied using impedance spectroscopy technique in the temperature range from 80 to 400 K and the frequency range from 40 to 107 Hz. DC measurements show that the studied structures exhibit semiconductor (SC) behaviour in all temperature range of study. AC data analysis show a transition from SC to metallic behaviour at 160

La0.6Ca0.3Ag0.1MnO3 system has been synthesized using the cheap solid–solid process. Structural analysis indicates that the sample exhibits a single phase of intragranular. Electrical and dielectric data, over a wide temperature range and frequencies have been recorded with impedance spectroscopy. We visualize the conductivity, whose activation energy is low, as a successive hopping of electrons as polaron does. Further, the conductivity is governed by the small polaron hopping model at higher temperature region while it fits well with the variable range hopping model at a lower temperature range. Dielectric data has been represented in different alternative complex formalisms, from which complementary information has been extracted. The complex impedance diagram suggests the contribution of only two active microstructures, ruling out the electrode polarization effect. We adopt the spectrum of the imaginary component of the electric modulus M″ to distinguish long range hopping from short range hopping. The relative permittivity spectrum permits to identify the possibility of the existence of electric polarizations. Further, it reveals colossal static dielectric constant, which makes it suitable for multitude potential applications in electronic industrial fields.

Graphene-ZnO (G-ZnO) nanocomposites were synthesized by simple and low cost co-precipitation and spin-coating technique. The graphene concentration has been tuned from 3 to 10 at. %. The microstructure and morphology of the synthesized nanocomposite was studied by X-ray diffraction (XRD), Raman spectroscopy and Scanning Electron Microscopy (SEM) techniques. Structural analysis by x-ray diffraction showed that G-ZnO was found to present hexagonal wurtzite–type structure and Raman spectroscopy showed the formation of graphene component. Compared to pure ZnO, photoluminescence (PL) intensity of the nanocomposites had decreased, due to quenching of photoemission, in the presence of graphene. The photo-response of the G-ZnO nanocomposite expands to the visible region up to 800 nm. A significant Photo-Electro-Chemical (PEC) activity enhancement has been observed for the 3 at.% graphene concentrated sample. Sensing characteristics of G-ZnO films was investigated. A strong improvement of the PEC efficiency has been obtained for the optimum G content of 3 at. %.