Changes In Conductivity Behavior Research Articles

Tuning Magnetoconductivity in LaMnO3 NPs through Cationic Vacancy Control.

The inclusion of La-Mn vacancies in LaMnO3 nanoparticles leads to a noticeable change in conductivity behavior. The sample retains its overall insulator characteristic, with a typical thermal activation mechanism at high temperatures, but it presents high magnetoconductivity below 200 K. The activation energy decreases linearly with the square of the reduced magnetization and vanishes when the sample is magnetized at saturation. Therefore, it turns out that electron hopping between Mn3+ and Mn4+ largely contributes to the conductivity below the Curie temperature. The influence of the applied magnetic field on conductivity also supports the hypothesis of hopping contribution, and the electric behavior can be explained as being due to an increase in the hopping probability via spin alignment.

Magnesium Spinel Ferrites Development for FDM 3D-Printing Material for Microwave Absorption

The magnesium nanosized ferrite powder with formula MgFe2O4 was synthesized via a pyrochemical sol–gel glycine–nitrate method and annealed consistently at temperatures of up to 1300 °C. The MgFe2O4 ferrite samples’ microstructure was studied by SEM and XRD methods. According to the results of the studies, the increase in MgFe2O4 nanoparticles size from about 15 nm to micron-sized particles was observed when increasing annealing temperatures. The DC electrical conductivity of MgFe2O4 also clearly shows the change in conduction behavior of samples with increased calcination temperatures. The electromagnetic microwave properties of micron-sized particles of MgFe2O4 ferrite powder for a 1200 °C annealing temperature were studied for composites in paraffin matrix with produced magnetic filler mass concentration at 40% and 50%. The filament composites of polymer polylactic acid with MgFe2O4 ferrite powder samples were prepared by the FDM 3D-printing process and their microwave-absorbing properties were investigated. The application of developed PLA–MgFe2O4 ferrite filament for fabricating magnetic microwave-absorbing components also was demonstrated.

Preparation and Characterization of B4C-HfB2 Composites as Material for High-Temperature Thermocouples

Boron carbide shows high thermoelectric power. Therefore, it is an interesting material for thermoelectric applications. In the past, there were already successful uses of boron carbide as a thermocouple material together with graphite. However, more reliable, cost-efficient, and long-term stable solutions are required for practical benefit. Boron carbide and hafnium boride composites were prepared by pressureless sintering of B4C and HfC powder mixtures. The effect of HfC addition on the sinterability of boron carbide was studied. Highly densified ceramic with a relative density of 95.4% was obtained at a sintering temperature of 2250 °C. The composition and the microstructure of the dense composites are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). In addition, the correlation between the composition, Seebeck coefficient, and the electrical conductivity was investigated. The Seebeck coefficient of the composite is decreased and the electrical conductivity is increased with the increasing addition of HfC, and a change in conduction behavior from semiconducting to a metallic mechanism is observed. Functional thermocouples based on the prepared composites were tested and showed potential for temperature measurement application.

Changes in the Structure and Properties of Nickel-Zinc Spinel Nanoferrites Series for 3D-Printing

The family of nickel-zinc nanoferrites with general formula NixZn1 – xFe2O4 for 3D printing were synthesized via pyrochemical urea-nitrate method and annealed at temperatures of up to 770 K. The ferrite powder microstructure was studied by SEM and XRD methods. Average nanocrystallite sizes of 21 to 32 nm and average nanoparticles sizes of 22 to 50 nm were determined. The DC electrical conductivity of NixZn1 – xFe2O4 clearly shows the change in conduction behavior of samples with increase in nickel content. The observed low electrical conductivity with values at 0.l-0.3 and 0.8-0.9 parts of nickel ion for NixZn1 – xFe2O4 is due to change in cation distribution in spinel structure. The microwave absorbing properties of ferrites at 9.15 GHz were analyzed by FMR and maximum microwave absorption is that of compositions NixZn1 – xFe2O4 with x = 0.15 – 0.30. Additive manufacturing FDM 3D-printing process with PLA-nanoferrite filament for fabricating magnetic components also was demonstrated.

Pressureless sintering and properties of boron carbide composite materials

AbstractBoron carbide and Tantalum boride composites were prepared by pressureless sintering of B4C with addition of TaC powder. The effect of TaC addition on the sinterability of boron carbide was studied. High densified ceramic with a relative density of 98.7% was obtained at sintering temperature of 2250°C. The composition and the microstructure of the dense composites are characterized by means of x‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDX). The studies show that the composites contain boron carbide, TaB2, and carbon phases with a homogeneous structure. In addition, the correlation between the composition and the electrical conductivity was investigated. The electrical conductivity of the composite increased with increasing addition of TaC, and a change in conduction behavior from semiconducting to metallic was observed. High hardness value of 28.49 ± 1.33 GPa was obtained by the sample with 30 wt% TaC addition.

New mixed ionic and electronic conductors based on LaScO3: Protonic ceramic fuel cells electrodes

In the present work, the well-known proton conducting oxide La0.9Sr0.1ScO3-δ (LSS) is modified by the introduction of transition metal cations into a Sc sublattice in order to enhance the electronic conductivity of the material. Introduced cations of transition metal are selected on the basis of their ion radii and the variety of oxidation state, thus the compositions under study are La0.9Sr0.1Sc1-xMexO3–α (LSSMe) (where Me is Ti, Fe, Co, Ni, or Mo). Introduction of more than 5 mol.% of a dopant leads to a change in conductivity behaviour on pO2 which means that the predominant disorder type shifts from ionic to electronic.Electrochemical performance is studied on both symmetric and fuel cells. Impedance spectra are analysed by means of the distribution of relaxation time (DRT) technique. Both cathodes and anodes have shown great electrochemical performance with polarization resistance at 800 °C as low as 0.005 Ohm*cm2 for the cathode and 0.039 Ohm*cm2 for the anode in wet (water vapour pressure (pH2O) = 2.5*10−2 atm) air and hydrogen respectively.

Activation–relaxation processes and related effects in quantum conductance of molecular junctions

We reveal the comparative relationship between small changes in quantum conductivity behavior for molecular junctions. We clarify the mechanisms of acquiring and losing additional thermal activation energy during average current flow in a gold-1,4 benzenediamine (BDA)-gold molecular junction and explain the quantum conductance modulation process. Small changes in working temperature lead to a change in quantum conductivity, which is reflected in random telegraph signal behavior. We demonstrate the high sensitivity of the BDA molecules to small changes in temperature. For BDA molecules, conductance thermo-sensitivity values are relatively high near to This advantage can be used to measure weak variations in the ambient temperature. We show that the additional thermal energy arising from the change in temperature can impact on the strength of the electrode-molecule coupling, on the modulation of quantum conductivity. Local changes in quantum conductance of the order of quanta or smaller are conditioned by small random changes in the working regime arising from some of the activation processes. On the basis of the modulation of conductance, we calculate the magnitude of the spring constant of the 1,4 benzenediamine molecule as at the stretching length of 0.03 nm for the Au−NH2 molecular junction.

Interface dominated conductivity change in Ce0.8Sm0.1Nd0.1O2−δ/La9.33Si6O26 composite electrolyte

Samarium and neodymium co-doped ceria (Ce0.8Sm0.1Nd0.1O2−δ abbreviated SNDC) and lanthanum silicate (La9.33Si6O26 abbreviated LSO) composite electrolytes with different mixing ratio were prepared at 1500 and 1550 °C. The composite obtained were all with high density, and no chemical reaction between two phases was observed during sintering according to the XRD result. The addition of LSO has a great influence on the suppression of grain growth of SNDC, and brought about the change in conduction behavior of composite. High distortion at hetero interface has been observed by TEM. The composite with 30 wt% LSO exhibits the highest conductivity (0.0036 S/cm at 500 °C) with an improvement of 37% compared with SNDC. The measurement at low oxygen partial pressure demonstrated the high chemical stability of composite electrolyte, making it a promising candidate for intermediate temperature SOFCs or oxygen sensors.

Elaboration and Characterization of Glasses and Ceramic-Glasses within Theternary Diagram Li<sub>2</sub>O-Cr<sub>2</sub>O<sub>3</sub>-P<sub>2</sub>O<sub>5</sub>

Use of the regular melting-quench method allowed the isolation of a small glass domain within the ternary system Li2O-P2O5-Cr2O3 at 1000°C. Electrical conductivity and dielectric permittivity measures on sample glasses and ceramic glasses of this domain were performed at a frequency of 10 kHz and at temperatures between 25°C and 300°C. The values of dielectric permittivity and electrical conductivity increase with increasing Li2O content. However, increases of Cr2O3 content, even at low concentrations, induce a change in electrical conductivity behaviour from that of a glass to that of a ceramic glass. The introduction of an increasing amount of Li2O content in vitreous phosphorus pentoxide changes its three-dimensional network; rupture of the P-O-P bond then occurs and there is formation of easily polarisable entities with quite high values of . The vibrational spectroscopy technique I.R has allowed an efficient investigation of the structural change versus composition within the above indicated ternary diagram. The maximal dielectric permittivity obtained at 300°C, both for the glasses and for the ceramic glasses varied in the order 104 to 3 × 105, while the maximum electrical conductivity obtained at 300°C for the ceramic glasses was in the order of 10-3 Ωcm-1.

Understanding the anomalous conduction behavior in ‘n’ type tungsten oxide thin film during hydrogen gas sensing: Kinetic analyses of conductance transients

Promising hydrogen sensing characteristics are reported for sol–gel synthesized ‘n’ type WO3 thin films. During hydrogen gas sensing using WO3 films, irrespective of the test gas concentration and thickness of the sensing films, a temperature dependent anomalous change in surface conduction behavior of the sensor is reported. The nature of such gradual change in conduction behavior was further investigated by analyzing the response and recovery conductance transients. It was identified that the observed anomalous characteristics are superposition of several donor and acceptor type adsorption–desorption processes with their characteristic time constants. From the temperature variations of these characteristic time constants we have estimated the activation energies of the processes involved during sensor response and recovery. By correlating the estimated activation energies with the steps of the surface reactions, we have made an attempt to explain the observed gradual change in conduction behavior of WO3 thin films during hydrogen gas sensing.

Electromechanical behavior of polyaniline/poly (vinyl alcohol) blend films under static, dynamic and time-dependent strains

We report on the experimentally observed electrical conductivity enhancement in polyaniline/poly (vinyl alcohol) blend films under uniaxial tensile loading. Polyaniline (PANI) is an intrinsically conducting polymer, which does not form stretchable free-standing films easily and hence its electromechanical characterization is a challenge. Blending of PANI with other insulating polymers is a good choice to overcome the processability problem. We report the electromechanical response of solution blended and HCl doped PANI/PVA blends subjected to uniaxial, static, dynamic and time-dependent tensile loading. The demonstrated viscoelastic and morphological contributions of the component polymers to the electrical conductivity behavior in these blends could lead to interesting applications in strain sensors and flexible electronics. The reversibility of the electromechanical response under dynamic strain is found to increase in blends with higher PANI content. Time-dependent conductivity studies during mechanical stress relaxation reveal that variations in the micro-domain ordering and the relative relaxation rate of the individual polymer phases can give rise to interesting electrical conductivity changes in PANI blends. From morphological and electrical conductivity studies, we show that PANI undergoes primary and secondary agglomeration behavior in these blends that contributes to the changes in conductivity behavior during the deformation. A 3D variable range hopping (VRH) process, which uses a deformable core and shell concept based on blend morphology analysis, is used to explain the experimentally observed electromechanical behavior.

Thermal conductivity of self-assembled nano-structured ZnO bulk ceramics

In this study, we describe the changes in thermal conductivity behavior of ZnO-Al micro- and nano-two-phase self-assembled composites with varying grain sizes. The reduction in thermal conductivity values of micro-composites was limited to ∼15% for ZnO-4% Al. However, nano-composites exhibited large reduction, by a factor of about three, due to uniform distribution of nano-precipitates (ZnAl2O4) and large grain boundary area. Interestingly, the micro-composites revealed continuous decrease in thermal conductivity with increase in Al substitution while the nano-composites exhibited the lowest magnitudes for 2% Al concentration. Raman spectra indicated that phonon confinement in ZnO-Al nano-composites causes drastic decrease in the value of thermal conductivity.

Controlled p-type to n-type conductivity transformation in NiO thin films by ultraviolet-laser irradiation

We report the systematic changes in structural, electrical, and optical properties of NiO thin films on c-sapphire introduced by nanosecond ultraviolet excimer laser pulses. Epitaxial nature of as deposited NiO was determined by x-ray diffraction phi scans and transmission electron microscopy (TEM) and it was established that NiO film growth takes place with twin domains on sapphire where two types of domains have 60° in-plane rotation with respect to each other about the [111] growth direction. We determined that at pulsed laser energy density of 0.275 J/cm2, NiO films exhibited conversion from p-type semiconducting to n-type conductive behavior with three orders of magnitude decrease in resistivity, while maintaining its cubic crystal structure and good epitaxial relationship. Our TEM and electron-energy-loss spectroscopy studies conclusively ruled out the presence of any Ni clustering or precipitation due to the laser treatment. The laser-induced n-type carrier transport and conductivity enhancement were shown to be reversible through subsequent thermal annealing in oxygen. This change in conductivity behavior was correlated with the nonequilibrium concentration of laser induced Ni0-like defect states.

Metal–insulator transition in Fe-substituted SrRuO 3 bad metal system

The effect of Fe substitution in the bad metal SrRuO 3 perovskite was studied by resistivity, magnetic susceptibility and Mössbauer spectroscopic measurements. The conduction behavior changed from metallic for x Fe≤0.1 to non-metallic for x Fe>0.26. In the intermediate concentration range, 0.1< x Fe<0.26, a resistivity minimum was observed as a function of temperature. The magnetic properties showed a change from ferromagnetic to paramagnetic for x Fe≥0.3. There was an enhancement in quadrupole splitting deduced from 57Fe Mössbauer spectra in going from compositions x Fe<0.3 to x Fe≥0.3 suggestive of a change in screening of ionic charge at this composition. These observations show that the change in conduction behavior of this system may be related to the initial small mean free path of the bad metal system as well as a change in conduction electron density brought about by substitution of trivalent Fe for quadruvalent Ru.

Electrical Properties of Cerium‐Doped BaTiO3

The high‐temperature equilibrium electrical conductivity of Ce‐doped BaTiO3 was studied in terms of oxygen partial pressure, P(O2), and composition. In (Ba1−xCex)TiO3, the conductivity follows the −1/4 power dependence of P(O2) at high oxygen activities, which supports the view that metal vacancies are created for the compensation of Ce donors, and is nearly independent of P(O2) where electron compensation prevails at low P(O2). When Ce is substituted for the normal Ti sites, there is no significant change in conductivity behavior compared with undoped BaTiO3, indicating the substitution of Ce as Ce4+ for Ti4+ in Ba(Ti1−yCey)O3. The Curie temperature (Tc) was systematically lowered when Ce3+ was incorporated into Ba2+ sites, whereas the substitution of Ce4+ for Ti4+ sites resulted in no change in this parameter.

A phase transition with an abrupt electrical resistivity change around 800 K in BaBi 0.5Pb 0.5O 3

Seebeck coefficient and electrical resistivity were measured in a temperature range of 300–1100 K in air for BaBi 1− x Pb x O 3 ( x=0, 0.25, 0.5, 0.75 and 1.0). The increase in Pb content led to the change in electrical conduction behavior from p-type semiconducting to n-type metallic and to n-type semimetallic, consistent with that in electronic structure previously reported on this alloy system. Two phase transitions were found at ∼650 K and ∼800 K for BaBi 0.5Pb 0.5O 3 from the temperature dependence of the electrical resistivity. With increasing temperature, the temperature dependence of the electrical resistivity for BaBi 0.5Pb 0.5O 3 showed a semiconductor-to-metal transition at ∼650 K with the continuous change in the resistivity and a metal-to-metal transition with an abrupt resistivity drop over ∼1.5 digits in a temperature range of 750–850 K (∼800 K). Combined with the powder X-ray diffraction (XRD) and Seebeck coefficient data, it is discussed that the semiconductor-to-metal transition at ∼650 K is due to the continuous proportionation of Bi cations into the chemical states closer to Bi 4+, and the metal-to-metal transition at ∼800 K may be due to the formation of a single chemical state with Bi 4+ which leads to the disappearance of the pseudogap at E F and the formation of a normal metal.

Oxide ion transport in highly defective cubic stabilized zirconias

Ac impedance spectroscopy and neutron powder diffraction have been used to study the high temperature behaviour of defective fluorite solid electrolytes. In yttria-stabilised zirconia with an yttrium content of 15 mol% YO1.5 there is a marked change in conductivity behaviour at around 650 °C, with a decrease in activation energy of 0.15 eV. Structural studies confirm that this is due to a change in the bulk of the sample with the disappearance of diffuse scattering peaks and marked changes in the behaviour of the isotropic temperature factors at the same temperature. These results indicate that the change in activation energy of yttria-stabilised zirconia at 650 °C is due to an order-disorder transition involving local defect clusters. In studies of zirconia co-doped with yttrium and niobium, activation energy for conduction is found to rapidly increase with the concentration of the trivalent yttrium Saturation doping is reached at about 20–30 % of yttrium and activation energy only increases slightly with doping. Introduction of pentavalent niobium at this level of doping serves to decrease activation energy, although it also decreases conductivity slightly. The low and high temperature activation energies converge as the saturation regime is approached. These observations seem to suggest that ordering of defect clusters into microdomains increases activation energy for ionic motion. At low defect concentrations and high temperatures, this local ordering breaks down and the activation energy for conduction decreases.

Phase Formation and Electronic Transport Properties in the Corundum (Ti 2O 3)-Ilmenite (MgTiO 3) System

At high temperatures the Ti 2O 3-MgTiO 3 system shows extensive solid solution formation with an order/disorder transition between ilmenite- and corundum-type structures. At lower temperatures (<1000°C), there exists a large immiscibility dome, extending from Mg 0.9Ti 1.1O 3 to Mg 0.4Ti 1.6O 3. Although X-ray peak intensities indicate a gradual change from order to disorder with composition, there is a discontinuity at the ilmenite/corundum boundary. The relationship between unit cell parameters and composition generally obeys Vegard's Law, apart from a deviation close to the Ti 2O 3 end member. Above 180 K thermally activated conductivity is observed, with a discontinuity at the corundum/ilmenite boundary. At lower temperatures, a change in conductivity behavior occurs, with a linear relationship between log resistivity and temperature being found up to 30 K in samples with low Ti oxidation state.

Chemistry and conductivity of some salts of polypyrrole

The structure of the conducting salts of polypyrrole (PP) can be modified by a) introducing substituents to the pyrrole ring, b) changing the salt structure by base/acid treatment and c) changing the counterion distribution via control of the size and conformation of polymeric counterions. A new synthetic route to bicyclic compounds containing the pyrrole ring allows the synthesis of better ordered polymers, but with lower conductivities as observed for PP salts. The chemistry of acid-base-treatment is analyzed electrochemically; it is believed that OH − attacks the oxidized PP in ß-position. The most dramatic changes in conductivity behavior are seen in samples prepared with polystyrene-sulfunate counterions in the presence of varying amounts of non-solvent. By controlling the density of counterion chain, one is able to monitor the size and structure of internal barriers to charge carrier mobility.