Field Dependence Of Current Density Research Articles

Structural, microstructural and electrical characteristics of Ca, Sn and Se modified Bi0.5Na0.5TiO3 ferroelectric ceramics

In this paper, studies of structural, microstructural and electrical properties of calcium, tin, and selenium modified bismuth sodium titanate (Bi0.5Na0.5TiO3) compound with a general chemical formula (Bi0.45Na0.45Ca0.1) (Ti0.9Sn0.05 Se0.05) O3, synthesized by a high-temperature mixed oxide reaction method, have been discussed. Analysis of room temperature X-ray diffraction data confirms the formation of perovskite single-phase compound with rhombohedral symmetry. The surface morphology of the sample exhibits the uniform distribution of grains of varying size. Studies of the electrical parameters (dielectric, impedance and conductivity) of the material, collected at various temperatures (75–375 °C) in a wide frequency range (1 kHz–1MHz) have provided its conduction and relaxation behavior. The electric field dependent current density (J-E) characteristics suggest the Ohmic behavior while the field dependent polarization (P-E loop) confirms the ferroelectric nature of the studied material.

Structural, dielectric, and electrical characteristics of selenium-modified BiFeO3–(BaSr)TiO3 ceramics

The selenium (Se)-modified 0.5BiFeO3–0.5(BaSr)TiO3 was synthesized employing a high-temperature solid-state technique. Structural analysis (through Rietveld refinement) of the room-temperature X-ray diffraction pattern and data of the material confirms the tetragonal (P4mm) symmetry of the compound. Studies of scanning electron micrograph (SEM) and energy dispersive X-ray spectroscopy (EDS) data reveal the nature and characteristics (i.e., size, shape and distribution of grains, grain boundaries, voids and presence of elements, etc.,) of surface morphology and structure of the compound. Detailed analysis of temperature and frequency dependence of dielectric and impedance data exhibits the relaxor type of ferroelectric behavior and semiconductor (negative temperature coefficient of resistance) nature of the material. The material is found to have high resistivity and low dielectric (tangent) loss. Study of the temperature dependence of leakage current characteristics (i.e., electric field dependent current density) shows the leaky behavior of the material. The Se-modified 0.5BiFeO3–0.5(BaSr)TiO3 (BFBST), compared to its components (BFBST and pure BiFeO3), material possesses different types of conduction process, like space charge limited (SCLC), Ohmic, Hopping type. Poole–Frenkel emission (PFE) and Schottky emission (SE) fitted data give an evidence/idea about the bulk-limited and interface-limited conduction mechanism present in the system. The energy gap values (Eg) of Se substituted BFBST and BiFeO3 are found to be 0.55 eV and 0.78 eV, respectively, in the low-temperature range.

Conduction through plasma-treated polyimide: analysis of high-field conduction by hopping and Schottky theory

Plasma surface modification of polyimide (PI) films has been used to modify the material’s wetting and adhesion properties but has also been found to impact high-field electrical properties. Previous work by Meddeb et al. (Chem Phys Lett 649:111–114, 2016. https://doi.org/10.1016/j.cplett.2016.02.037 ) demonstrates a significant reduction in high-field leakage current at high temperatures because of O2 plasma treatment of PI. In this study, we investigate field-dependent current density [J(E)] data measured in our previous study by Meddeb et al. (2016) to identify the surface and bulk mechanisms responsible for high-field conduction behavior of O2 plasma-modified PI films. Specifically, we analyze the J(E) data using three conduction theories: Poole–Frenkel, Schottky, and Hopping. Poole–Frenkel and Schottky analyses are performed by the implementation of linear regression. Hopping analysis was performed using a rigorous statistical technique that incorporates nonlinear regression as well as a bootstrap statistical analysis of fit parameters. Analysis of J(E) data over the temperature range 25–175 °C indicates that 13-micron-thick untreated PI films are dominated by a hopping process at lower temperatures; however, transition to Schottky-dominated conduction occurs as temperature is increased. Films treated with O2 plasma show similar characteristics to the untreated set: Hopping dominated conduction at low temperatures with gradual transition to Schottky. However, the transition to Schottky conduction occurs at a higher temperature in plasma-treated films in comparison with the untreated control set. These results are verified by (1) extracting dielectric permittivity from Schottky plots as a function of temperature and (2) a statistical interpretation of confidence intervals calculated for hopping fit parameters used in low-temperature nonlinear regression. Outcomes from theoretical analysis of the data are used to provide further insight into how surface chemistry may be tailored to limit high-field leakage current in polyimides and insulating polymers in general.

Role of nano and micron-sized inclusions on the oxygen controlled preform optimized infiltration growth processed YBCO superconductors

In the present work, with the aim of improving the local flux pinning at the unit cell level in the YBa2Cu3O7-δ (YBCO) bulk superconductors, 20wt% of nanoscale Sm2O3 and micron sized (Nd, Sm, Gd)2BaCuO5 secondary phase particles were added to YBCO and processed in oxygen controlled preform optimized infiltration growth process. Nano Dispersive Sol Casting method is employed to homogeneously distribute the nano Sm2O3 particles of 30–50nm without any agglomeration in the precursor powder. Microstructural investigations on doped samples show the chemical fluctuations as annuli cores in the 211 phase particles. The introduction of mixed rare earth elements at Y-site resulted in compositional fluctuations in the superconducting matrix. The associated lattice mismatch defects have provided flux pinning up to large magnetic fields. Magnetic field dependence of current density (Jc(H)) at different temperatures revealed that the dominant pinning mechanism is caused by spatial variations of critical temperatures, due to the spatial fluctuations in the matrix composition. As the number of rare earth elements increased in the YBCO, the peak field position in the scaling of the normalized pinning force density (Fp/Fp max) significantly gets shifted towards the higher fields. The curves of Jc(H) and Fp/Fp max at different temperatures clearly indicate the LRE substitution for LRE' or Ba-sites for δTc pinning.

High Field Characterization of Current-Voltage Dependences in Continuous/Semicontinuous High-k Ultrathin Films Through Leakage-Path Blocking

We developed a ferroelectric assisted current-voltage characterization technique for continuous/semicontinuous high-k ultrathin films under the field as high as 17 MV/cm without invoking of dielectric breakdown. The leakage current of the ultrathin films equals domain switching current with breakdown paths blocked efficiently by underneath ferroelectric thick layer. The extracted field dependences of current density for a 1– 6 nm thick Al2O3 layer deposited on top of a 300 nm thick Pb(Zr,Ti)O3 layer obey the equation of Schottky mission. This technique is helpful for investigations of high-field charge emission and quantum physics for ultrathin films in loss of the atomic-layer flatness.

A rational consideration of space charge

Space charge formation and its increase with field under DC conditions is not a mystical phenomenon. The increase in space charge with applied field is an obvious and inevitable result of the interaction of field-dependent current density with spatially inhomogeneous resistivity. For common polymeric dielectrics, the current density makes a transition from a linear function of field to an exponential function of field at around 10 kV/mm. This causes a similar transition in the sample space charge in the same field region. However, this transition has no obvious connection with aging, and if it does prove to have a connection, the driving force is the rapidly increasing current density and not the space charge, which is a result thereof. As to the issue of the accuracy of space charge measurements, it may be more important to focus on providing a physical mechanism for 1-eV deep traps at an average separation of 3 nm within a polymeric dielectric. This would bring about the ability to engineer important dielectric properties as well as improved understanding of the physical basis of aging and other important phenomena in dielectrics.

Reply to comment by John H. Helsdon Jr. on “On the roles of deep convective clouds in tropospheric chemistry”

Reply to comment by John H. Helsdon Jr. on “On the roles of deep convective clouds in tropospheric chemistry”

Correlation of charge transport to local atomic strain in Si-rich silicon nitride thin films

Charge transport in Si-rich silicon nitride thin films is investigated. Over a composition range from Si3N4 to SiN0.54 the field dependent current density is observed to increase by as much as seven orders of magnitude, the residual Si–N bond strain decreases from 0.006 to −0.0026 and the Poole–Frenkel barrier height, ΦB, decreases from 1.08 to 0.55 eV. A direct correlation between ΦB and the local atomic strain is observed. It is concluded that reductions in ΦB are a manifestation of compositionally induced strain relief at the molecular level. Reductions in ΦB result in increased Poole–Frenkel emission rates and consequently higher conductivities in Si-rich films.

Electrical transport properties in passivated magnetic small iron particles

Electrical transport properties of a sample composed of small iron particles of several tens nm was studied in the temperature range 1.8–300 K. TEM study indicates that each small particle is covered with a very homogeneous epitaxial γ-Fe 2O 3 shell that prevents further oxidization of the metal particles. The temperature dependence of resistivity R( T) and the field-dependent current density in the high-field range can be well described by the theory of fluctuation-induced tunneling conduction.

Improved strain tolerance in aligned-MgO-whisker reinforced (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ tapes

The strain tolerance of monofilamentary BSCCO 2223 tapes has been improved by reinforcing with aligned-MgO whiskers. Tapes reinforced with 15 vol.% whiskers are found to exhibit a superconducting transition temperature of 106 K and a critical current density of 2/spl times/10/sup 4/ A/cm/sup 2/ at 77 K. The magnetic field dependence of current density of the reinforced tapes is found to be identical to that the unreinforced tapes. The reinforced tapes are found to sustain 90% of their initial current density even at a bend strain of 0.6%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>