Extrinsic Conduction Research Articles

Insight into the Critical Role of Oxygen Vacancies and V=O Bonds Length in V2O5 for Advanced Zinc Ion Storage.

Due to the larger sizes and stronger positive polarity of Zn2+ than dominant univalent ions, Zn2+ sluggish diffusion within V2O5 host electrodes is an essential issue in developing aqueous zinc-ion batteries (ZIBs) of higher energy densities. Herein, a high-performance V2O5 cathode was developed through subtly synthesizing and tuning V2O5 with oxygen vacancies-enriched and elongated apical V=O1 bond by altering the gradient concentration of hydrazine hydrate in the gas-solid reaction system. This strategy can enhance both intrinsic and extrinsic conductivity to a large extent. The electrochemical testing demonstrated the oxygen vacancies-enriched and elongated apical V=O1 bond can not only increase the intrinsic electronic conductivity of V2O5, but also induce additional pseudocapacitance to enhance the Zn2+ diffusion kinetics. We used infrared spectroscopy and Raman spectroscopy to characterize the change in the bond length structure of V2O5. Simultaneously, the long-term cyclability (capacity retention of 76.9 % after 1200 cycles at 4.0 A g-1) and rate capabilities (218 mAh g-1 at 4.0 A g-1) are promoted as well. We believe that our work might shed light on the bond length engineering of V2O5 and provide insights for the reasonable designing of novel cathodes for practical rechargeable ZIBs.

Extrinsic and intrinsic nonlinear Hall effects across Berry-dipole transitions

Three-dimensional Hopf insulators are a class of topological phases beyond the tenfold-way classification. At the critical point of the transition between two distinct Hopf insulators with rotational symmetry, the band-touching points are point Berry dipoles with two opposite Berry charges overlapping in a mirror-symmetric way, and carry unique Berry curvature structures leading to a special quantization of Berry flux. Close to such Berry-dipole transitions, we find that the extrinsic and intrinsic nonlinear Hall conductivity tensors in the weakly doped regime are characterized by two universal functions of the ratio between doping level and bulk energy gap, and are directly proportional to the change in Hopf invariant across the transition. Our work suggests that the nonlinear Hall effects display a generalized-sense quantized behavior across Berry-dipole transitions, establishing a correspondence between nonlinear Hall effects and Hopf invariants.

High hole mobility and non-localized states in amorphous germanium

Covalent amorphous semiconductors, such as amorphous silicon (a-Si) and germanium (a-Ge), are commonly believed to have localized electronic states at the top of the valence band and the bottom of the conduction band. Electrical conductivity is thought to occur through the hopping mechanism via these localized states. The carrier mobility of these materials is usually very low, in the order of ∼10−3–10−2 cm2/Vs at room temperature. In this study, we show that pure high-density amorphous Ge has exceptionally high carrier mobility, in the order of ∼100 cm2/Vs, and a high hole concentration of ∼1018 cm−3. The temperature-dependent conductivity of the material is also very-well defined with two distinctive regions, extrinsic and intrinsic conductivity, as in crystalline Ge. These results provide direct evidence for a largely preserved band structure and non-localized states within the valence band in high-density amorphous Ge, as previously suggested by Tauc et al. from optical characterization alone.

Spin Conductivity Based on Magnetic Toroidal Quadrupole Hidden in Antiferromagnets

We report our theoretical results on spin conductivity in antiferromagnets by focusing on the role of the magnetic toroidal quadrupole (MTQ) in electron systems. The MTQ is characterized as a time-reversal-odd rank-2 polar tensor degree of freedom in electrons, which is distinct from conventional rank-1 magnetic and magnetic toroidal dipoles. Based on a microscopic sd model analysis for a tetragonal system under both collinear and noncollinear antiferromagnetic orderings, we clarify that the MTQ becomes a source of an extrinsic spin conductivity even with neither a uniform magnetization nor spin–orbit coupling. We also list all the magnetic point groups to accommodate the MTQs as a primary order parameter as well as the candidate antiferromagnetic materials.

Tuning the electrical conductivity of Rare Earth-doped BaTiO3 using Gd2O3 as an exemplar

The electrical properties of Gd-doped BaTiO3 ceramics prepared by various doping mechanisms have been investigated using Impedance Spectroscopy and correlated with the proposed doping mechanisms observed from phase diagram studies and with solution energies obtained from atomistic simulations. Undoped BaTiO3, BaTi1-xGdxO3-x/2, Ba1-y/2Ti1-y/2GdyO3 and Ba1-zGdzTi1-z/4O3 were prepared. The first two series and y < 0.10 samples possess extrinsic p-type conduction due to oxygen gain (oxidation) associated with the presence of oxygen vacancies. A core-shell microstructure causes electrical heterogeneity where y < 0.10. For y ≥ 0.10, oxygen vacancies are eliminated by substitution of a small excess of Gd3+ at the Ba-site leading to intrinsic (band-type) conduction. All Ba1-zGdzTi1-z/4O3 ceramics processed in air exhibit n-type semiconductivity that is attributed to a small amount of oxygen loss (reduction) during sintering. The oxygen loss can be prevented by processing ceramics in a flowing O2 atmosphere.

Properties and Applications of Metal Phosphates and Pyrophosphates as Proton Conductors.

We review the progress in metal phosphate structural chemistry focused on proton conductivity properties and applications. Attention is paid to structure–property relationships, which ultimately determine the potential use of metal phosphates and derivatives in devices relying on proton conduction. The origin of their conducting properties, including both intrinsic and extrinsic conductivity, is rationalized in terms of distinctive structural features and the presence of specific proton carriers or the factors involved in the formation of extended hydrogen-bond networks. To make the exposition of this large class of proton conductor materials more comprehensive, we group/combine metal phosphates by their metal oxidation state, starting with metal (IV) phosphates and pyrophosphates, considering historical rationales and taking into account the accumulated body of knowledge of these compounds. We highlight the main characteristics of super protonic CsH2PO4, its applicability, as well as the affordance of its composite derivatives. We finish by discussing relevant structure–conducting property correlations for divalent and trivalent metal phosphates. Overall, emphasis is placed on materials exhibiting outstanding properties for applications as electrolyte components or single electrolytes in Polymer Electrolyte Membrane Fuel Cells and Intermediate Temperature Fuel Cells.

Microscopic physical origin of polarization induced large tunneling electroresistance in tetragonal-phase BiFeO3

Ferroelectric tunnel junctions have attracted intensive research interest due to the fundamental physics and potential applications in high-density data storage and neuromorphic computation. However, the intrinsic physical origin, especially at atomic scale, of polarization-controllable tunneling current is still controversial due to the degradation of ferroelectric polarization and the extrinsic conduction induced by defects or oxygen vacancies. Here, a large tunneling electroresistance effect of over 10,000% in a thick (∼15 nm) tetragonal-phase BiFeO3 thin film is observed, where a nanoscale point-contact geometry is delicately designed to reduce the extrinsic defect effects. By combining transmission electron microscopy and first-principles calculations, the atomic and electronic structures of BiFeO3 tunneling layer are investigated. The corresponding results indicate the different charge transfer occurs at the top and bottom interface, which induces distinct tunneling barrier asymmetry when the polarization direction is opposite.

Conduction mechanism in excess Bismuth doped Strontium Bismuth Niobate ceramics

Strontium Bismuth Niobate ceramics with excess Bismuth doping (0%wt – 20%wt) were prepared using solid state reaction method. X-ray diffraction studies reveal the decrease in c-axis orientation as bismuth content increases up to 5 ​wt%, beyond that it increases. The dielectric studies were carried out at room temperature as well as at higher temperatures. The ferroelectric properties were found to improve with excess bismuth doping to some extent (5%), indicating compensation for bismuth losses during heat treatment. Temperature dependent dc conductivity studies were done and attempts were made to explain extrinsic and intrinsic conduction mechanisms in Strontium Bismuth Niobate. In low temperature region, the activation energy was found to be very low (0.08eV–0.16eV), which increases (1.07eV–1.14eV) due to introduction of intrinsic defects. A detailed conduction mechanism is presented with excess bismuth doping in Strontium Bismuth Niobate.

Role of carbonaceous matrix and nobel metal doping to boost the electrochemical aptitude of nanostructured MoO3

Elevated specific capacitance (Csp), higher surface area, faster charge transport, exceptional chemical stability, lower diffusion resistance, and a porous structure are the key features of the ideal electrode material. Undoubtedly, transition metal oxides (TMOs) have a better Csp, but their limited surface, bulky structure, and lower conductivity are the main obstacles to limiting their applications as an electrode material. So we adopted several strategies to fabricate the MoO3 electrode, an ideal electrode because of its integrated electrochemical characteristics. Firstly, the MoO3 sample was manufactured at the nanoscale to tune the specific surface area, reduce the bulk contribution, and minimize the diffusion resistance. Secondly, a doping strategy has been used to get an Ag-doped MoO3 sample with enhanced intrinsic conductivity. The carbonaceous nanomaterials, especially reduced graphene oxide (rGO), due to their exceptional electrical conductivity, good chemical stability, higher surface area, and distinctive structure, have an excessive aptitude to boost the electrochemical aptitude of transition metal oxides. Therefore, thirdly, we used a composite formation strategy to fabricate a rGO/Ag/MoO3 nanocomposite with improved extrinsic conductivity and faster charge transfer characteristics. Finally, we decorated the rGO/Ag/MoO3 sample on the current collector via the Nafion binder because of its superior charge transfer characteristics. The nanocomposite-based electrode exhibited excellent Csp (422.16 F/g @ 1 Ag), exceptional rate performance (>33% at 7 fold higher current density) and superior cyclic stability (88.21% after 5000 cycles). These remarkable and integrated electrochemical characteristics of the nanocomposite are the outcome of the synergistic belongings of all adopted strategies. The electrical and electrochemical results suggest that using several strategies to make the perfect electrode is a productive approach.

Synthesis and electrical properties of 2,9(10),16(17),23(24){4-[bis[2-(hydroxy)ethyl]amino}benzyloxy-phthalocyaninatozinc(II)

A novel zinc phthalocyanine with four 4-bis(hydroxyethylamino)benzyloxy groups was synthesized and characterized by using IR, 1H and 13C NMR and UV-VIS spectral data. Also, some physical analyses were carried out on this new zinc phthalocyanine. Conductivity, dielectric and impedance properties of the sample were investigated in the temperature range of 300–525 K and the frequency range of 100–10 MHz. It has been found that DC conductivity can be explained by Arrhenius type conductivity and the transition is from extrinsic conduction to intrinsic conduction. AC conductivity exhibits an almost linear behavior with frequency explained by the quantum mechanical tunneling (QMT) model. The dielectric constant decreased with increasing frequency, but instead increased with increasing temperature. This is an indication that dielectric dipoles are thermally active. From the results obtained by impedance spectroscopy, it was found that the relaxation process is a Cole-Cole model.

Intrinsic and extrinsic conduction contributions at nominally neutral domain walls in hexagonal manganites

Conductive and electrostatic atomic force microscopy (cAFM and EFM) are used to investigate the electric conduction at nominally neutral domain walls in hexagonal manganites. The EFM measurements reveal a propensity of mobile charge carriers to accumulate at the nominally neutral domain walls in ErMnO3, which is corroborated by cAFM scans showing locally enhanced direct current conductance. Our findings are explained based on the established segregation enthalpy profiles for oxygen vacancies and interstitials, providing a microscopic model for previous, seemingly disconnected observations ranging from insulating to conducting behavior. In addition, we observe variations in conductance between different nominally neutral walls that we attribute to deviations from the ideal charge-neutral structure within the bulk, leading to a superposition of extrinsic and intrinsic contributions. Our study clarifies the complex transport properties at nominally neutral domain walls in hexagonal manganites and establishes the possibility to tune their electronic response based on oxidation conditions, opening the door for domain-wall-based sensor technology.

Structure, Dielectric Properties and Impedance Spectroscopy of BaTi0.97(Zn,V,Ta)0.03O3 Ceramics

BaTi0.97Zn0.01V0.01Ta0.01O3and#172; sample was prepared using the conventional mixed oxide sintering route. The samples were characterized using X-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy and Impedance spectroscopy. Structure of the sample was analyzed using Rietveld analysis which showed the formation of tetragonal symmetry. Raman spectroscopy was also in agreement with the XRD results, further indicating the ferroelectric signature in the sample. Electrical microstructure analyzed by impedance spectroscopy analysis revealed two electroactive regions in the sample, belonging to the grain boundary and bulk. An extrinsic conduction mechanism was observed across the sample. Dielectric properties as a function of temperature demonstrated phase transition (TC) at ~ 94 and#176;C, with relative permittivity ~ 3280 at TC. Antiferroelectric-like double hysteresis loops were observed in P-E analysis. The energy storage density was calculated to be 0.26 J/cm3 at an electric field of 50 kV/cm, indicating that BaTi0.97Zn0.01V0.01Ta0.01O3and#172; ceramics can be potentially useful base materials for high density energy storage capacitors.

Structure, Dielectric Properties and Impedance Spectroscopy of BaTi0.97(Zn,V,Ta)0.03O3 Ceramics

BaTi0.97Zn0.01V0.01Ta0.01O3and#172; sample was prepared using the conventional mixed oxide sintering route. The samples were characterized using X-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy and Impedance spectroscopy. Structure of the sample was analyzed using Rietveld analysis which showed the formation of tetragonal symmetry. Raman spectroscopy was also in agreement with the XRD results, further indicating the ferroelectric signature in the sample. Electrical microstructure analyzed by impedance spectroscopy analysis revealed two electroactive regions in the sample, belonging to the grain boundary and bulk. An extrinsic conduction mechanism was observed across the sample. Dielectric properties as a function of temperature demonstrated phase transition (TC) at ~ 94 and#176;C, with relative permittivity ~ 3280 at TC. Antiferroelectric-like double hysteresis loops were observed in P-E analysis. The energy storage density was calculated to be 0.26 J/cm3 at an electric field of 50 kV/cm, indicating that BaTi0.97Zn0.01V0.01Ta0.01O3and#172; ceramics can be potentially useful base materials for high density energy storage capacitors.

The effect of external temperature gradients on thermal conductivity in non-equilibrium molecular dynamics simulations: From nanowires to bulk Si

Nonequilibrium molecular dynamics is widely used to calculate the thermal conductivity of various materials, but the influence of temperature gradient to thermal conductivity has received limited attention within current research studies. The purpose of this article is to explore the discrepancy between intrinsic and extrinsic thermal conductivities under different temperature gradients, which can be considered as external fields. The analyses of phonon density of states have shown that the temperature gradient plays a role in the external field, and a larger temperature gradient activates more low-frequency vibrational modes, which leads to larger thermal conductivities. Specially, the thermal conductivity increases linearly with the temperature gradient when using Stillinger-Weber (SW) potential. Moreover, a new formula was derived to satisfactorily fit the thermal conductivities of bulk Si and silicon nanowires (SiNWs) for various cell sizes, and the physical meaning of the formula was explained. It is shown that the SW potential and Tersoff potential of Si produce different thermal conductivities. By comparing the results of first principles simulations, the Tersoff potential gives rise to better description of vibrational modes.

Impedance Spectroscopy of Vanadium Pentoxide Thin Films

V2O5 thin films have been deposited onto an insulating support by radiofrequency (rf) reactive sputtering from a metallic vanadium target at controlled flow rates of argon–oxygen gas mixture. Glancing-incidence x-ray diffraction (GIXD) analysis and scanning electron microscopy (SEM) were used for structural and phase characterization of the obtained materials. The as-sputtered thin films were found to consist of orthorhombic V2O5 phase. Electrical properties were determined by electrochemical impedance spectroscopy (EIS) conducted over the frequency range of 0.1 Hz to 1.4 MHz and temperatures ranging from room temperature (RT) to 773 K. Between RT and 528 K, the recorded impedance spectra were interpreted in terms of an equivalent circuit composed of a resistor and non-Debye constant-phase element (CPE) connected in parallel. In this temperature range, the material exhibited n-type extrinsic conductivity. The activation energy of electrical conductivity was 0.243 ± 0.023 eV. At 528 K, an abrupt change in resistivity was observed, interpreted as a metal–insulator transition (MIT). Above 528 K, the equivalent circuit was composed of a resistor (R) and inductor (L) connected in series, typical of materials exhibiting metallic properties.

Polymer Nanocomposites of Surface‐Modified Graphene. I: Thermal and Electrical Properties of Poly(Vinyl Alcohol)/Aminoacid‐Functionalized Graphene

Extrinsic electrically conducting polymer composites are versatile materials for applications in sensors, electrical components, antistatic coatings, among others. The use of carbon‐based conducting loads, such as graphene, in polymer nanocomposites allows the manufacturing of suitable electrically conducting films for a variety of applications. In our work, graphene sheets are covalently modified with histidine, phenylalanine, or beta‐alanine aminoacids, in order to improve dispersion and impart extrinsic conductivity to poly(vinyl alcohol) (PVA) films. The presence of organic groups in the surface of graphene sheets improved their dispersion in polymer matrices. In addition, such benign surface modifiers are suitable to produce environmentally friendly, electrically conducting loads for polymer nanocomposites. Our findings showed that aminoacid‐functionalized graphenes have good dispersability, resulting in semiconducting nanocomposite films with preserved thermal stability, suggesting that these carbon‐based nanoloads are suitable additives for PVA in applications including antistatic paints and coatings.

Humidity sensing characteristics of Sb2O3 thin films with transitional electrical behavior

The quest for smaller and more efficient humidity sensors is still on. Antimony trioxide thin films deposited by vacuum thermal evaporation onto heated glass substrates are analyzed as water vapor sensors, along with the study of their morpho-structural and electrical properties. Several substrate temperatures were set during the depositions, leading to films with significantly different electrical and humidity sensing features. Unusual increase of the electrical resistance of the films with temperature above 170 °C was noticed, representing the intermediate stage between extrinsic and intrinsic conductivity. In the extrinsic conduction region, the activation energy decreases exponentially with the substrate temperature during the initial depositions. The alternative current (AC), i.e. the electrical frequency characteristics versus humidity were also studied, allowing for the identification of the conduction mechanism within the samples, which is most probably short range hopping of charge carriers through trap sites, influences by the changing grain size and remanent amorphous phase within the films.

Effect of doping on the structure, piezoelectric and electrical properties of Aurivillius type Ca0.6(Na0.5Bi0.5)0.4Bi2Nb2O9 ceramics

Aurivillius phase [Ca0.6(Na0.5Bi0.5)0.4]1−x(LiCe)x/2Bi2Nb2O9 (CNBNLC-100x, x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ceramics were prepared by the conventional solid state method. The LiCe substitution induced structural distortion and orthorhombic distortion of CNBNLC-100x ceramics which influenced piezoelectric activities and Curie temperature, respectively. The results implied that the more structural distortion of lattice leads to higher piezoelectricity. CNBNLC-8 ceramics with ultrahigh TC of 904 °C had a high piezoelectric activity of 17.6 pC/N, even after annealing at 600 °C for 2 h, the d33 value of CNBNLC-8 ceramics still retained 62.5% of its original value. Ce4+ as donor dopant, the dc resistivity of CNBN ceramics increased with the substitution of Ce4+ for Ca2+. At high temperature region, the extrinsic conductivity changes of the ceramics from p-type to n-type with the increase of Ce4+ doping amount. Further investigation demonstrated that the ac conductive process of ceramics referred to three different mechanisms. The main conduction mechanisms were considered as first-order ionization of oxygen vacancies, second- order ionization of oxygen vacancies and intrinsic dc conductivity at three temperature regions, respectively. All these good electrical properties provided the LiCe doped CNBN ceramics with a large potentiality for high-temperature piezoelectric applications.

Transport properties in Sb-doped SnO2 thin films: Effect of UV illumination and temperature dependence

Films of Sb-doped SnO2 were deposited by dip-coating technique. The morphology analysis showed that the microstructure of the samples exhibits many shaped nano-sized crystallites homogenously dispersed on the surfaces. The roughness varies with Sb-content, implying that doping has an important effect on the surface morphology of the films. Raman and FTIR-ATR investigations revealed that the films exhibit a vibration mode at 564 cm−1 ascribed to the amorphous phase overlapping the crystallites. Thus, the selection rule (k=0) is relaxed because of disorder and reduced crystallites size to nanoscale by Sb-doping, which may explain the broadening and shift of the lattice modes. The vibration of sub-bridging oxygen atoms seems to be significantly affected by oxygen vacancies and Sb-derived surface mode has been identified at 578 cm−1. The optical band gap is red-shift due to the introduction of localized states in the SnO2 bulk associated to Sb-doping and oxygen defects. The refractive index varies due the enhanced grain boundaries effect and surface disorder induced by Sb incorporation in the crystal lattice. The photoconductivity (σac) shows a dispersion pattern with two regions, corresponding to extrinsic and intrinsic conductivities. Under UV-illumination, the electrical charge transport mechanism changes from multi-hopping to single-hopping at higher temperatures.

The effect of oxide additives on the transport properties of cesium nitrite

Conductivity of composite solid electrolytes (1 − x) CsNO2–xA (A =MgO, Al2O3, SnO2) was systematically investigated. It was found that in all cases heterogeneous doping leads to the increase in the conductivity. Conductivity goes through a maximum as a function of the oxide concentration that is explained by additional contribution of the interface regions. However, in contrast to known composites, at small concentration of oxides the character of the Arrhenius dependences is similar to that of pure cesium nitrite, where intrinsic and extrinsic conductivity regions are observed. At high concentration of the heterogeneous dopant the character of Arrhenius dependences changes and no change in slope of the Arrhenius dependences is observed. According to thermal analysis data, at high concentration of oxide amorphous interface-stabilized phase of CsNO2 forms on the oxide interface. Composite solid electrolytes based on CsNO2 with additives of nanocrystalline γ-alumina and SnO2 have a high ionic conductivities exceeding 10−2 S/cm at 356 °C. Composites containing additives of MgO have lower conductivity despite of high specific surface area.