The paper presents investigations of frequency and temperature dependences on capacitance, phase shift and loss tangent of nanocomposites (FeCoZr)x(CaF2)(100−x) of the metallic phase content x = 66.3 ...at.%. The sample was subjected to 15 min annealing at temperature 723 K. It has been established that within the range of 50 Hz–5 × 104 Hz the frequency dependence on capacitance and conductivity is weak. Further frequency increase brings about rapid decrease of capacitance and the conductivity growth. Those both processes can be described with the same relaxation time value of ca 5 × 10−7 s. Based on the Arrhenius plots, activation energy values have been determined and they are of ca 0.112 eV and 0.0134 eV for the conductivity and permittivity, respectively. It is consistent with the model of hopping recharging, which shows that the permittivity activation energy should be lower than the conductivity activation energy. It has been established, that order of the permittivity activation energy is comparable to the potential energy of the interaction between elementary charges, negative and positive (dipole) ones located in adjacent potential wells.
•(FeCoZr)x(CaF2)(100−x) nanocomposites deposited in the Ar atmosphere.•Frequency and temperature dependences of Cp, σ, θ and tan δ have been defined.•Activation energy values have been determined as ca 0.112 eV for the conductivity.•Activation energy values have been determined as ca 0.0134 eV for the permittivity.
Though controversially discussed, understanding of the electronic properties of B4.3C, carbon-rich limit of the homogeneity range has meanwhile reached an advanced degree. In contrast, the knowledge ...on more boron-rich boron carbides has remained small. As a contribution for closing this gap, we present a study of the electrical conductivity from ∼5 to ∼2100 K. Numerous samples covering the whole homogeneity range came from various sources and were differently prepared, thus allowing to separate intrinsic effects from those of impurities, density and preparation method. We show that at low temperature, the electrical conductivity meets formally Mott's law of variable-range hopping. However, its parameters are incompatible with experimental results and need redefinition. At high temperatures, the electrical conductivity is thermally activated. The activation energies yield the energetical position of gap states above the valence band, which are related to intrinsic defects in the structure depending on the actual chemical composition.
Electrical conductivity of B4.3C boron carbide. Display omitted
•The electrical conductivity of boron carbide is studied between 5 and 2100 K in the whole homogeneity range.•Effects of various structural defects are recognized.•Specific gaps states are identified acting at high and low T in different function, each.•At high T the electrical conductivity is thermally activated, while at low T Mott's law of variable range hopping is formally met.•In the case of boron carbide, the parameter σ0 of Mott's law require redefinition.
Graphene oxide (GO) contains several chemical functional groups that are attached to the graphite basal plane and can be manipulated to tailor GO for specific applications. It is now revealed that ...the reaction of GO with ozone results in a high level of oxidation, which leads to significantly improved ionic (protonic) conductivity of the GO. Freestanding ozonated GO films were synthesized and used as efficient polymer electrolyte fuel cell membranes. The increase in protonic conductivity of the ozonated GO originates from enhanced proton hopping, which is due to the higher content of oxygenated functional groups in the basal planes and edges of ozonated GO as well as the morphology changes in GO that are caused by ozonation. The results of this study demonstrate that the modification of dispersed GO presents a powerful opportunity for optimizing a nanoscale material for proton‐exchange membranes.
Oxidized: The reaction of graphene oxide (GO) with ozone results in a high level of oxidation that leads to a significantly improved ionic (protonic) conductivity of GO. This effect originates from enhanced proton hopping, which is due to the higher content of oxygenated functional groups in the basal planes and edges of the ozonated GO as well as the morphology changes that are caused by the ozonation.
We expand the temperature interval of the resistivity measurement to clarify the charge transport mechanisms in the rare-earth nickelates ReNiO3. Thin films of LaNiO3 demonstrate an expected metallic ...behavior at high temperatures: a perfect linear rise of the resistivity ρ∝T is confirmed above room temperature. However, NdNiO3 films characterized by a sharp metal-to-insulator transition display a noticeable deviation of their high-temperature resistivity from the metallic linear relation. This deviation is suggested to originate from an additional thermally activated hopping transport. High-temperature hopping conductivity is also found in SmNiO3 films. Carrier localization due to disorder and the formation of small polarons is discussed as being responsible for hopping.
•We measure the resistivity of rare-earth nickelates films up to temperature of 800 K.•LaNiO3 films demonstrate a linear rise of the resistivity above room temperature.•High-temperature hopping conductivity is found in the films of NdNiO3 and SmNiO3.•Small-polaron hopping could explain the charge transport anomalies in nickelates.
In this paper, we report some physical properties of AgAlP
2
O
7
compound obtained through the standard solid-state reaction technique. AgAlP
2
O
7
has been studied by X-ray diffraction, Raman ...spectroscopy and impedance spectroscopy. The title compound crystallized at room temperature (
T
= 300 K) in the monoclinic system with P2
1/c
space group. The electrical properties were studied over a wide range of temperature (440–640 K) in the frequency range of 40 Hz–10 MHz. Study of frequency dependence of AC conductivity suggests that the material obeys the Jonscher’s universal dynamic law. The conductivity is equal to 9.37 × 10
−5
Ω cm
−1
at 640 K, and it is thermally activated with activation energy of 0.76 eV. The variation of DC conductivity with temperature follows the Arrhenius behavior. The calculated values of
s
decreased with temperature. This behavior reveals that the conduction mechanism is correlated with barrier hopping. The binding energy
W
m
and the hopping distance
R
ω
were deduced.
Owing to their exceptional mechanical, electrical and thermal properties, carbon nanotubes (CNTs) are ideal candidates for improving the performances of polymer composites. In the present work, we ...investigated the effect of CNT addition on the electrical conductivity of two types of carbon black (CB) filled polymer. Also, two different methods of compounding were applied and their effects are compared: mixing by a laboratory compounder Haake Rheomix Polylab and mixing by a twin-roller mixer.
Composites containing a total of 10% by weight of different carbon fillers (CB, CNTs and their mixtures in a ratio of 8/2) were thus obtained, characterized by scanning electron microscopy and their frequency dependence of the electrical conductivity was measured.
It is shown that the alternating current (AC) conductivities display two regions: a low frequency region of constant conductivity and a higher frequency region of increasing conductivity with increasing frequency (following the percolation scaling law). It was also observed that the samples compounded with twin-roller mixer exhibit a higher electrical conductivity than those obtained with the laboratory compounder. Moreover, the conductivity of the composites containing CNTs in addition to CB is found to be higher than the conductivity of the composites containing only CB.
Temperature dependent conductivity measurements were performed on phosphine doped hydrogenated amorphous silicon grown by plasma enhanced chemical vapor deposition over a range of argon dilution and ...phosphine PH3 doping. Resistance curve derivative analysis was used along with hopping conductivity modeling to determine the nature of the conduction mechanism. The results of this analysis show that anomalous hopping conduction, where lnσ∝T−p with p≈0.75, describes the temperature dependent conductivity of most of the samples studied, and represents the first observation of anomalous conduction in phosphine doped amorphous silicon. Argon dilution modifies the efficiency of dopant incorporation into electrically active sites, and the resultant defects within the silicon network appear to sufficiently modify the density of states, leading to anomalous conduction. Raman spectroscopy was used as additional evidence of these structural changes.
Epitaxial chromium ferrite (Fe sub(2)CrO sub(4)), prepared by state-of-the-art oxygen plasma assisted molecular beam epitaxy, is shown to exhibit unusual electronic transport properties driven by the ...crystallographic structure and composition of the material. Replacing 1/3 of the Fe cations with Cr converts the host ferrimagnet from a metal into a semiconductor by virtue of its fixed valence (3+); Cr substitutes for Fe at B sites in the spinel lattice. By contrast, replacing 2/3 of the Fe cations with Cr results in an insulator. Three candidate conductive paths, all involving electron hopping between Fe super(2+) and Fe super(3+), are identified in Fe sub(2)CrO sub(4). Moreover, Fe sub(2)CrO sub(4) is shown to be photoconductive across the visible portion of the electromagnetic spectrum. As a result, this material is of potential interest for important photo-electrochemical processes such as water splitting. A qualitatively different mode of conductivity is activated in magnetite by doping one third of the Fe cation sites with Cr. Experimental data and ab initio modeling results establish the structure, and then point to different electron hopping paths becoming operative, as Cr super(3+) replaces Fe super(3+) in the octahedral sites of the spinel lattice.
PDF
