Change In Conduction Mechanism Research Articles

Enhancement in photodetection properties of Ag/CdS/Ag devices through novel rare-earth metal Tb doping

Herein, the effect of Terbium (Tb) doping on the photodetection properties of Ag/CdS/Ag devices have been elucidated. An enhancement in the photodetector performance was noted for Ag/Tb@CdS/Ag device in terms of amplified sensitivity of 592, improved responsivity of 3.64 A/W, and excellent detectivity of 6.39 × 1012 Jones in compared to pure Ag/CdS/Ag device with respective values of 192, 0.24 A/W and 7.98 × 1011 Jones. Moreover, the Tb-doped device exhibits a faster response time of 30 ms as compared to 421 ms for device with pure CdS. The enhancement in photodetector performance was explained through the change in conduction mechanism from Schottky in Ag/CdS/Ag to ohmic in Ag/Tb@CdS/Ag device.

Hall Effect Characterization of α‐Irradiated p‐Type 4H‐SiC

Most electrical characterization of radiation damage to semiconductors is conducted on full devices or on low‐doped material. However, evaluating the radiation hardness is challenging in less mature semiconductor systems where low‐doped material is unavailable and full devices are difficult to realize. Herein, temperature‐dependent Hall effect measurements are used to demonstrate α particle‐induced radiation effects in p‐type 4H‐SiC with a room temperature hole concentration of . The 4H‐SiC is irradiated by α particles from a 210Po source over a fluence of –. Modeling the hole concentration as a function of temperature shows that α radiation causes hole compensation through the introduction of hole traps. The radiation also induces a reduction in hole mobility due to an increase in defect‐related scattering centers. At low temperatures and increasingly higher fluences, the conduction mechanism changes from band conduction to another mechanism.

Effect of Brønsted Acidity on Ion Conduction in Fluorinated Acetic Acid and N-Methylimidazole Equimolar Mixtures as Pseudo-protic Ionic Liquids.

To clarify proton conduction mechanism in protic ionic liquids (PILs) and pseudo-PILs (pPILs), equimolar mixtures of N-methylimidazole (C1Im) with fluorinated acetic acids were investigated by Raman spectroscopy, X-ray scattering, and dielectric relaxation spectroscopy (DRS). Only the ionic species exist in the equimolar mixture of C1Im and HTFA (HTFA: trifluoroacetic acid). On the other hand, the equimolar mixture of C1Im and HDFA (HDFA: difluoroacetic acid) consists of both ionic and electrically neutral species. In particular, not only the electrostatic but also van der Waals interactions with the F atoms were observed in the liquid structures of both [C1hIm+][TFA-] and [C1hIm+][DFA-]. The concept for proton conduction mechanism that we have proposed in previous study was revisited; the proton conduction mechanism could be classified with two linear free energy relationship lines for proton exchange reaction and translation/rotation of proton carriers. Our results exhibit that the proton conduction mechanism changes from proton hopping to vehicle mechanism with increasing acidity of an acid HA in PILs.

Investigation of physical properties of manganite on example of Sm0.35Pr0.2Sr0.45MnO3

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 ε’ 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.

Effect of cobalt ion contamination on proton conduction of ultrathin Nafion film

With the wide use of platinum alloy electrocatalysts proton exchange membrane fuel cells, the dissolution of transition metal in the acid environment of catalyst layer becomes a major concern due to the decreased catalytic activity during long-term operation. Although great efforts have been done, few attention is paid to the effect of transition metal ion contamination of Nafion ionomer that wrapped around catalyst particles within catalyst layer which might greatly influence the proton conduction. To elucidate such effect, ultrathin Nafion film on SiO2 model substrate is prepared via self-assembly method to represent the ionomer in fuel-cell catalyst layers, and the ultrathin film with specific thickness is further equilibrated in Co(NO3)2/HNO3 solutions with different Co2+ concentration to achieve different doping level. Conductivity measurements demonstrate that the non-precious metal contamination severely worsens proton conduction of Nafion ionomer, but it is always ignored before. In addition, when the occupation of H+ in Nafion ionomer is less than 50%, the activation energy shows a sharp increase, indicating a possible change in proton conduction mechanism.

Ba doping induced modifications in the structural, morphological and dielectric properties of double perovskite La2NiMnO6 ceramics

We report the modifications in the structural, morphological and dielectric properties of La2NiMnO6 (LNMO) by doping Ba at La site for three different proportions. These ceramics were successfully synthesized by the solid-state route as revealed by the X-ray diffraction patterns of three compositions. The sample phases were confirmed by the Rietveld refinement which showed monoclinic symmetry having P21/n space group. The scanning electron microscopy imaging of the pristine LNMO sample reveals ablated spheres, and this gets modified to sugar-cube like structures after the Ba substitution at La site. In addition to modification in morphology, a decrease in porosity is also noticed after Ba doping as calculated from the ratio of pore-pixels to the entire pixel-count of the image which reveals the percent porosity. The substitution of Ba2+ in place of La3+ is expected to bring about changes in the overall conduction mechanisms and also the dielectric relaxations in the LNMO. The temperature-dependent (100K–400K) and frequency-dependent (1 ​kHz–2 ​MHz) dielectric studies reveal that the Ba doping results in the decrease of dielectric constant and dielectric loss. This decrease is attributed to conversion between Ni2+ to Ni3+ and Mn4+ to Mn3+ due to Ba doping resulting in an increase of grain resistance as such decreasing possibility of most of the electrons to reach grain boundaries, which in turn causes a decrease in polarization and thus resulting in the decrement in the value of dielectric constant. Low dielectric materials are preferable and more reliable as they cause low heat dissipation and reduce any parasitic capacitance, thus allowing faster switching speeds in the fabricated devices.

Effects of Mn doping on ferroelectric, ferromagnetic and optical properties of BiFeO3 thin films

Mn-doped BiFeO3 films were prepared by chemical solution deposition method on fluorine doped tin oxide conductive glass via spin-coating technique. XRD pattern reveals the presence of the impurity phase of Bi2Fe4O9 in BiFeO3 films, while no impurity phase is found in the Mn-doped thin films. XPS spectrum demonstrates the purity of prepared thin films by exhibiting the desired elements alone and it also shows that Mn-doping restrains the change of Fe3+ valency. The leakage current result shows that Mn-doping causes the change of conduction mechanism led by the change of microstructure and the restraint of Fe ions valence. BiFe0.95Mn0.05O3 thin film has a good ferroelectric performance with high remnant polarization (Pr) value of 27 μC/cm2. Mn doped BiFeO3 films have stronger saturation magnetization than the BiFeO3 thin films. UV vis NIR transmittance spectra depicts the optical property, which shows the optical band gap decreases with the concentration of Mn increases.

Change of high-voltage conduction mechanism in vertical GaN–on–GaN Schottky diodes at elevated temperatures

Current-voltage-temperature characteristics (0 °C to 150 °C) of SBDs on highly compensated 15 μm and 30 μm n-type GaN drift layer were measured for voltages up to −300 V and up to −800 V, respectively. When the temperature is between 75 °C and 100 °C, both SBDs exhibited a similar change in conduction mechanism from thermionic field emission (TFE) to thermionic emission (TE) due to the activation of N-vacancies (VN) (Ea = −1.67 ± 0.02 eV). However, at high voltages when the temperature is >100 °C, the conduction mechanism changes from TE to TFE due to the de-trapping of electrons from activated carbon-traps (Ea = +0.69 eV) in the grown drift layers.

Effect of Temperature on Electrical Conductivity of Zinc Oxide Polyvinyl Alcohol Nanocomposites

A set of zinc oxide (ZnO)/polyvinyl alcohol (PVA) nanocomposites were prepared by mixing presynthesized zinc oxide nanoparticles and polyvinyl alcohol (PVA) in different weight percentages with solution casting technique.Different characterization methods are carried out to determine the material properties. The effects of ZnO nanoparticles loading level on electrical properties of the nanocomposites were investigated in details. The intermolecular interactions within the polymer nanocomposites were explored by FTIR and XRD. The formation of nanocomposites and changes were investigated by SEM analysis.It showed that ZnO nanoparticles were homogeneously dispersed throughout the whole polymeric matrix. DC conductivity was measured in the temperature range 70-300K and it obeys Arrhenius relation. Activation energies were evaluated from Arrhenius plots for all compositions. The samples show a semiconductor-like behavior in regions I (300-130 K) and II (130-70K).The activation energies are smaller at lower temperature range as compared to higher temperature range. The change in conduction mechanism arises at different temperatures, which are feature of the samples. As the ratio of ZnO to polymer changes these switching positions are shifted to upper temperatures. All the composites obey the Arrhenius equation for the conductivity mechanism which confirms that the nanocomposites are thermally activated. The dc conductivity of all the samples follows a simple hoping type of charge conduction method. This is evident from Fourier Transform Infrared Spectroscopy (FTIR) studies.

Preparation and properties of BaCe1-xYxO3- based composites with Ba–Ce–Y–Si–P–O glass

The aim of this work was to determine the influence of glassy Ba–Ce–Y–Si–P–O phase, prepared by sol-gel method and introduced into the BaCe0.9Y0.1O3 host material on the selected properties of obtained materials. Three composite materials with different content of modifying phase (3, 6 and 18 wt%) were prepared. It was found that the introduction of an additional amorphous phase leads to the decrease of the electrical conductivity in the measured temperature range, both in grain interior and grain boundary regions. The observed change of conduction mechanism can be explained by the modification of the chemical composition of BaCe0.9Y0.1O3 due to reaction with modifying phase at the stage of material preparation. Based on obtained results further optimisation of modifier phase composition and the preparation conditions leading to the materials with improved properties can be proposed.

Superprotonic Conductivity in Metal-Organic Framework via Solvent-Free Coordinative Urea Insertion.

Highly stable superprotonic conductivity (>10-2 S cm-1) has been achieved through the unprecedented solvent-free-coordinative urea insertion in MOF-74 [M2(dobdc), M = Ni2+, Mg2+; dobdc = 2,5-dioxido-1,4-benzenedicarboxylate] without an acidic moiety. The urea is bound to open metal sites and alters the void volume and surface functionality, which triggers a significant change in proton conductivity and diffusion mechanism. Solid-state 2H NMR revealed that the high conductivity was attributed to the strengthening of the hydrogen bonds between guest H2O induced by hydrogen bonds in the interface between H2O and the polarized coordinated urea.

Transport and magnetic phenomena in ZnO-С thin-film heterostructures

Abstract ZnO- and C-based heterostructures were fabricated by the layer-by-layer deposition technique using the ion-beam sputtering process. Structure, electrical and magnetic properties of fabricated heterostructures are discussed. The two-phase (ZnO and C) films are evolved into a multilayer structure, consisting of amorphous carbon and crystalline ZnO layers when the bilayer thickness increases. When carbon is added to ZnO, its electrical resistivity reduces. The conduction mechanism changes from the variable-range hopping in a narrow energy band to the nearest neighbors hopping in ZnO–C films with a thickness of h

Structural, magnetic, and electrical characterization of Sr-substituted LaFeO3 perovskite synthesized via sucrose auto-combustion route

In this work, a series of Sr-substituted lanthanum orthoferrite perovskites, La1−xSrxFeO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), were prepared using the sucrose-assisted auto-combustion route to study the effect of Sr-substitution on the structural, magnetic, and electrical properties and to investigate the impact of the entire method on different properties. The auto-combustion process and the perovskites formation were followed using differential thermal analysis–thermogravimetry techniques. The obtained different phases were characterized using X-ray diffractometer (XRD), Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy HRTEM measurements. XRD revealed peaks attributed to SrCO3 secondary phase increases in their intensity by increasing Sr-content till predominate at x = 1.0. It also showed a transfer from orthorhombic symmetry to rhombohedral one by increasing Sr-content. The obvious contraction in the unit cell parameters by Sr-substitution could be attributed to the Fe3+ → Fe4+ oxidation occurred to balance the total charge on molecule. The obvious increase in the magnetization by increasing Sr could be attributed to the formation of Fe4+ ions, strengthening the ferromagnetic component through sharing in the double-exchange interaction, Fe4+–O–Fe3+, as well as the formation of oxygen vacancies that disturb the uncompensated surface spin. Ac-conductivity measurements indicated a change in the entire conduction mechanism from electronic to ionic with improving conductivity by increasing Sr-content. Generally, the utilized sucrose method indicated an improvement in the obtained magnetization accompanied by lowering conductivity than previously reported systems in literature.

Evidence for dielectric suppression in non-magnetic modified multiferroic bismuth ferrite

Structural, magnetic, and electrical properties of polycrystalline Y-Sc codoped BiFeO3 (BFO) ceramics are investigated. Rietveld refinement and Raman spectroscopy analysis provide strong evidence of structural distortion without changing the structure of parent compound (rhombohedral: R3c) after codoping. Distortion due to nonmagnetic codoping marks an abrupt change in magnetic and electrical properties of BiFeO3. Ferromagnetic property is enhanced with a maximum remanent magnetization of 0.0045 emu/g at higher Sc-concentrations. Codoping improves the ferroelectric properties [Pr=13μC/cm2 at (Y,Sc)=(0.03,0.05)] due to the suppression of oxygen vacancies. The frequency-dependent dielectric properties at various temperatures are investigated. The relaxation peak shifts toward room temperature for Bi1−xYxFe1−yScyO3 ceramics, which eventually appeared above 100°C for parent BFO. The suppression of relaxation peak indicates the change in conduction mechanism for codoped ceramics. The conduction process and the relaxation mechanism in parent and Y-Sc codoped BiFeO3 are investigated with electrical modulus and impedance spectroscopy. Frequency-dependent ac conductivity at various temperatures indicates that the conduction mechanism follows the correlated barrier hopping model and is thermally activated. Temperature dependent conductivity studies at different frequencies reveal that the relaxation process in codoped ceramics is due to the long-range oxygen vacancy movement and the low loss values.

Structural, magnetic and electronic properties of Ti-doped BaFeO3-δ exhibiting colossal dielectric permittivity

We report a systematical investigation of the structural, magnetic, electronic, and dielectric properties of BaFe1-xTixO3-δ (x = 0.05, 0.10, 0.15 and 0.20) samples synthesized via the solid-state reaction method. Rietveld refinement using a combination of room-temperature X-ray (XRD) and neutron powder diffraction (NPD) data confirms single phases with a 6H-type structure for all the samples. X-ray absorption spectroscopy (XAS) study reveals a coexistence of Fe3+ and Fe4+, whose ratio remains almost unchanged with increasing Ti concentration. Magnetization measurements reveal a low-temperature inhomogeneous magnetic state with coexisting ferromagnetic (FM), AFM clusters and a paramagnetic phase. Moreover, magnetization of x = 0.10 shows a pinched hysteresis loop behavior, suggesting the coexistence of hard and soft FM phases in samples with high Ti concentrations. Low-temperature NPD measurements also confirm the absence of any long-range magnetic order in the samples. A colossal dielectric permittivity and two relaxation processes are observed for most of the studied samples. There is a change in electric conduction mechanism from the small polaron hopping to the Mott's variable-range hopping with increasing Ti concentration.

High sensitivity and selectivity chlorine gas sensors based on 3D open porous SnO2 synthesized by solid-state method

Abstract A simple solid-state reaction method was employed to synthesize the three-dimensional open porous SnO2 (3D OP-SnO2) by grinding the mixture of tin tetrachloride pentahydrate, sodium hydroxide and sodium chloride. Sodium chloride worked as a template to build the 3D open porous structure. The morphological feature was three-dimensional open porous with diameters about 300–500 nm and the edge of the 3D open porous were composed of numerous SnO2 nanoparticles with grain size around 5.8 nm. The chlorine (Cl2) gas sensing properties of 3D OP-SnO2 and bulk SnO2 (B–SnO2) sensors were systematically investigated. Gas response of the 3D OP-SnO2 sensor was 792.85 to 5 ppm Cl2 at 160 °C, which was 61 times higher than that of B–SnO2. Such outstanding gas sensing performance was mainly ascribed to the small grain size, which resulted in the change of conductivity mechanism and the decreased mobility of electrons. Thereby, the resistance of OP-SnO2 increased dramatically. Moreover, the unique structure and abundant oxygen vacancies also contributed to the excellent gas sensing performance, because they can elevate the specific surface area and provide sufficient Cl2 adsorption sites.

Influence of Slight Substitution (Mn/In) on Thermoelectric and Magnetic Properties in Chalcopyrite-Type CuInTe2

Alternative energy sources such as thermoelectric materials can play an important role to deal with waste heat problems. Currently new and improved thermoelectric materials are in high demand for energy harvesting from waste heat. In this research we synthesized and investigated thermoelectric and magnetic properties of CuIn1-xMnxTe2 where x = 0.0, 0.01, 0.02. All samples were densified by spark plasma sintering. Powder x-ray diffraction confirmed phase pure tetragonal structure for all nominal compositions with space group I–42d. Electrical resistivity showed a slight decrease upon Mn-doping, while the Seebeck coefficient was not reduced by doping, resulting in an enhanced power factor. Furthermore, relative power factor with respect to x = 0 as a function of temperature revealed the nature of the conduction mechanism changes after 450 K. It is observed that power factor enhancement was significant in the extrinsic region. Magnetic susceptibility verses temperature graphs showed paramagnetic behavior with a large negative Weiss temperature, which suggest relatively large antiferromagnetic interactions. Thermal conductivity decreased by 15–20% upon Mn-doping. Therefore, Mn-doping gives a totally positive effect on the figure of merit (ZT). Highest ZT value of 0.82 was observed for x = 0.02 at 854 K, which is close to 30% higher than non-doped sample.

Reverse design of negative permittivity property in Nickel-Network/Epoxy composites

Epsilon-negative materials are usually prepared by additive manufacturing, while a reverse design method needs to be developed to construct the epsilon-negative materials by subtractive manufacturing. Here the Nickel-Network/Epoxy composites were prepared via a chemical corrosion and curing process. The connectivity of nickel network was weakened by chemical corrosion, which was companied with a change of conductivity mechanism from metal-type conductivity to the hopping conductivity. The negative permittivity value could be effectively adjusted by corroding the nickel network, which was attributed to low-frequency plasmonic state of nickel network. The reverse design method provided a novel and more flexible method to construct the desired the epsilon-negative materials.

Структура и электрические свойства тонких пленок (ZnO/SiO-=SUB=-2-=/SUB=-)-=SUB=-25-=/SUB=-

Multilayer (ZnO/SiO2)25 thin films with a bilayer thickness of 6 to 10 nm has been synthesized in a single deposition process. The structure of the films consist of nanocrystalline ZnO layers and layers of amorphous SiO2. An analysis of the temperature dependences of the electrical resistivity, showed that a consistent change of the dominant conduction mechanism are realized in (ZnO/SiO2)25 thin films at temperatures 77 – 300 K: variable length hopping mechanism in a narrow energy band near the Fermi level at temperatures 77 – 250 K changed by the thermal activated impurity conductivity at close to room temperatures. The density of localized states and the activation energy of impurity conductivity has been estimated. The effect of heat treatment on the structure and electrical properties of the synthesized films has been investigated. It was found that the chemical interaction between the ZnO and SiO2 layers occurs at 580–600°C. It accompanied by the destruction of the multilayer structure and the appearance of the chemical compound Zn2SiO4 with the tetragonal structure (I-42d space group).

Effect of Heat Treatment on the Electrical Properties of Thin Yttrium-Doped In2O3 Films

Thin indium oxide films and In–Y–O films containing 0.7 to 3.6 at % Y have been grown by ionbeam sputtering of an indium target and a composite (indium + weighed amounts of yttrium) target in a mixture of argon and oxygen. The thin indium oxide films have a cubic crystal structure (sp. gr. Ia $$\bar 3$$ ). The incorporation of yttrium atoms into indium oxide leads to the formation of an amorphous structure in the as-grown films and an increase in their room-temperature electrical resistance by several orders of magnitude. Lowtemperature electrical resistance data indicate a change in conduction mechanism. High-temperature heat treatment of the thin In–Y–O films leads to the crystallization of their amorphous structure and an increase in their electrical resistance.