Direct Current Measurements Research Articles

Multiple magnetic transitions and complex magnetic behaviour of the perovskite manganite NdMn7O12

An A-site-ordered quadruple perovskite NdMn7O12 was prepared at high pressure of about 6 ​GPa and high temperature of about 1570 ​K. Its crystal structure was refined from synchrotron X-ray powder diffraction, and it crystallizes in space group I2/m at room temperature. One structural phase transition was detected at 664 ​K by differential scanning calorimetry. Three magnetic phase transitions were found in NdMn7O12 at TN1 ​= ​84 ​K, TN2 ​= ​12 ​K, and TN3 ​= ​9 ​K by specific heat and direct current magnetic measurements. Alternating current magnetic measurements revealed additional frequency-dependent features: anomalies near 82 ​K (at Hac ​= ​5 ​Oe), anomalies spanning between TN2 and about 70 ​K with maxima near 17 ​K, and anomalies near 6 ​K. Small kinks were found on dielectric constant at TN1 and TN2, and much stronger frequency-dependent steps on dielectric constant were observed between 20 and 35 ​K accompanied by sharp dielectric loss peaks; peak shifts followed the activation law. Pyroelectric current measurements did not detect any intrinsic ferroelectric polarization. Magnetic behaviour of NdMn7O12 is more complex than that of other members of the RMn7O12 family (R is a rare-earth cation).

Mictomagnetism and suppressed thermal conduction of the prototype high-entropy alloy CrMnFeCoNi

• CrMnFeCoNi is found to be mictomagnetic. • There is weak lattice anharmonicity in CrMnFeCoNi. • The thermal conductivity is reduced down to about 10% of nickel due to disorder scattering. • Lattice of CrMnFeCoNi is remarkably softened compared to nickel. High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices, differing from traditional alloys. Here, we investigate the magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering. Direct-current and alternating-current magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions below room temperature and three anomalies are found at about 80, 40, and 20 K, which are related to the paramagnetic to antiferromagnetic transition, the antiferromagnetic to ferromagnetic transition, and the spin freezing, respectively. The electrical and thermal conductivities are significantly reduced compared to Ni, and the temperature dependence of lattice thermal conductivity exhibits a glass-like plateau. Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.

A New Approach for Solving the False Balance of a Closed-Loop Fluxgate Current Transducer

The closed-loop fluxgate current transducer (CFCT) is the only current sensor whose measurement accuracy can reach a level of the parts per million (ppm) at present. However, the false balance, which makes the CFCT unable to work, caused by an excessive offset current is the inherent flaw of the CFCT. The high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i> (rate of current change) of the primary current is the main factor resulting in the offset current overload. Therefore, the CFCT is currently only applied for steady-state direct-current measurements. In this article, an approach is proposed to eliminate the false balance of the CFCT in the dynamic process by adding a feedforward branch, which provides a follow-up bias point for the CFCT to make the CFCT always work in a small-signal range, where a risk of magnetic saturation does not arise. The zero-flux state of the CFCT still only depends on the feedback branch, so its high measurement accuracy is maintained. The experiments prove that the CFCT can measure a flat-top pulsed current with an accuracy of the ppm level by this method.

Groundwater Contaminants Investigation in a Basement Area of Nigeria Using 2D Electrical Surveying Methods

Some of the common methods of monitoring and mapping groundwater contaminants is by extracting and analyzing samples of the groundwater obtained from wells within the expected investigation area, although lots of limitations are encountered in this type of investigation technique (point wise method) due to the nature of most subsurface layers, which are heterogeneous and anisotropic in nature and acquiring information using this method is comparatively difficult due to the few points acquired for investigation. Common and most recent method used to overcome such type of limitation and improve ground monitoring cost-effectively, is the use of Direct Current Resistivity measurements. This method gives a comprehensive characterization of the electrical properties of the subsurface layers (volume) needed. This paper investigates the usability and advantages of the resistivity method as a better method technique in monitoring groundwater contaminants in basement area or terrains under different seasons, in monitoring programmes. The work comprises field investigations at several sanitary landfills around the basement area of Ado-Odo town, in Ogun State, Nigeria, using Wenner array configuration (tomography) technique. From the results obtained, the level/degree of contaminants are easily identified and evaluated within the subsurface layers. We therefore concluded that the use of resistivity survey method gives an improved, better and appropriate information, generally suitable for mapping and monitoring of conductive groundwater contaminants in basement area.

Investigation of Polyvinyl Alcohol-CuS Compound with Metal-Like Conductivity

PVA-CuS compound produced from hybrid interpolymeric polyvinyl alcohol (PVA)-CuCl2 complex through solid state sulfurization was investigated by means of X-ray diffraction, UV-Vis and Raman spectroscopy, and direct current measurements. It is claimed that CuS in this compound has one-dimensional structure. This result is achieved by using a precursor technique based on diffusion limitation at solid state synthesis, so that the structure of initial reagents is inherited by reaction products. The produced material is determined to possess metal-type conductivity and thermopower in the vicinity of room temperature. Keywords: hybrid interpolymeric complexes, polyvinyl alcohol, CuS, inorganic polymers, one-dimensional structures, electrical properties.

Experimental study of elements of a Josephson traveling-wave parametric amplifier on SQUID chains.

The issues of designing a Josephson traveling-wave parametric amplifier (JTWPA) based on a well-established technology of superconducting microcircuits with given and controlled parameters based on high-quality Nb-AlOx-Nb tunnel junctions are considered. This technology has been adapted and optimized to obtain structures with the required parameters and circuits with large number of tunnel junctions. To advance the technology, the basic elements of a promising JTWPA have been devel-oped, manufactured and studied. In direct current measurements, a number of super-conducting elements parameters were experimentally determined; these parameters are required for designing a JTWPA chips for microwave measurements. An original design of JTWPA based on a chain of SQUIDs in a coplanar line has been developed for implementation using the IRE niobium technology; the parameters of the main elements of the JTWPA have been determined. Keywords: Josephson travelling-wave parametric amplifiers (JTWPA), Josephson metamaterials (JMM), Josephson junctions (JJs), cold amplifier, coplanar lines, quantum noise, SIS, SQUIDs.

Экспериментальное исследование элементов джозефсоновского параметрического усилителя бегущей волны на цепочке СКВИДов

The issues of designing a Josephson traveling-wave parametric amplifier (JTWPA) based on a well-established technology of superconducting microcircuits with given and controlled parameters based on high-quality Nb-AlOx-Nb tunnel junctions are considered. This technology has been adapted and optimized to obtain structures with the required parameters and circuits with large number of tunnel junctions. To advance the technology, the basic elements of a promising JTWPA have been devel-oped, manufactured and studied. In direct current measurements, a number of super-conducting elements parameters were experimentally determined; these parameters are required for designing a JTWPA chips for microwave measurements. An original design of JTWPA based on a chain of SQUIDs in a coplanar line has been developed for implementation using the IRE niobium technology; the parameters of the main elements of the JTWPA have been determined.

Effective tuning of magnetic anisotropy in distorted pentagonal bipyramidal Ni(II) complexes via substitution of axial coligands.

A series of Ni(II) complexes with pyridine-based macrocyclic ligand L (3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1(18),14,16-triene) with general formula [Ni(L)(X)2]0/2+ (X = Br- (1), I- (2), CH3CN (3), NCS- (4), imidazole (5)) was prepared and thoroughly investigated. X-ray molecular structures confirmed pentagonal bipyramidal geometry for all studied complexes with a strong Jahn-Teller distortion in the pentagonal equatorial plane and significantly elongated Ni-O distance(s) with a decrease of this distortion by varying axial coligands (CH3CN > Br- > I- > NCS- > imidazole). Direct current magnetic measurements revealed the easy-axis type of magnetic anisotropy with negative as well as positive axial zero-field-splitting parameter D ranging from +6.8 to -14.5 cm-1, which remains not affected in the halogenido series Cl- → Br- → I-, but which increases in the series with N-axial ligands in order CH3CN → NCS- → imidazole. Theoretical calculations helped to elucidate (i) the final coordination numbers 6 + 1 for 1 and 2, and 5 + 2 for 2-5, (ii) the pattern of splitting of d-orbitals, contributions of excited states to the final D-values and their final signs, and (iii) the complexity in the variation of the D and E parameters with elongation of axial bond distances in such strongly distorted systems. The studied complexes did not show any alternating magnetic susceptibility signal, but it was clearly documented that the magnetic anisotropy of the pentagonal bipyramidal Ni(II) complexes can be modulated/tuned by variation of axial coligands. Nevertheless, great care has to be taken for symmetry of the equatorial ligand field.

Ruddlesden–Popper Oxychlorides Ba3Y2O5Cl2, Sr3Sc2O5Cl2, and Sr2ScO3Cl: First Examples of Oxide-Ion-Conducting Oxychlorides

Oxide-ion conductors are attractive materials due to their wide applications such as solid oxide fuel cells (SOFCs). Crucial to the developments of the applications is the discovery of a class of oxide-ion conductors. Some Ruddlesden–Popper (RP) oxychlorides are expected to show high oxide-ion conductivity, because they have larger free and lattice volumes than RP oxides, leading to low activation energies. Here, we discover RP oxychlorides Ba3Y2O5Cl2, Sr3Sc2O5Cl2, and Sr2ScO3Cl as a class of oxide-ion conductors. Rietveld analyses of X-ray powder diffraction data indicate that Ba3Y2O5Cl2 and Sr3Sc2O5Cl2 are tetragonal I4/mmm n = 2 RP phases and that Sr2ScO3Cl is a tetragonal P4/nmm n = 1 RP phase. The predominant conducting species in Ba3Y2O5Cl2, Sr3Sc2O5Cl2, and Sr2ScO3Cl is strongly suggested to be the oxide ion by (i) direct-current (DC) polarization measurements, (ii) electrolyte domains observed in the oxygen partial pressure dependence of DC electrical conductivities at constant temperatures, and (iii) wide optical band gaps. DFT calculations of Ba3Y2O5Cl2 show a lower energy barrier for oxide-ion migration than that for chloride-ion migration, which supports the oxide-ion conduction. The DFT results indicate that oxide ions in Ba3Y2O5Cl2 two-dimensionally migrate mainly through equatorial oxygen O1 sites along the O1–O1 edge of the YO5 square pyramid. The oxide-ion conductivity of Ba3Y2O5Cl2 is considerably higher than that of Sr3Sc2O5Cl2, mainly due to a lower activation energy for conductivity, which can be ascribed to the larger free and lattice volumes of Ba3Y2O5Cl2. The DFT energy barrier for oxide-ion migration and experimental activation energy for bulk conductivity in Ba3Y2O5Cl2 are as low as those of a leading oxide-ion conductor La0.9Sr0.1Ga0.95Mg0.05O3−δ. Thus, the present work suggests that RP oxychlorides are a class of potential oxide-ion conductors.

Synthesis, Crystal Structures, and Spectroscopic Properties of Novel Gadolinium and Erbium Triphenylsiloxide Coordination Entities.

In alkali metal and lanthanide coordination chemistry, triphenylsiloxides seem to be unduly underappreciated ligands. This is as surprising as that such substituents play a crucial role, among others, in stabilizing rare oxidation states of lanthanide ions, taking a part of intramolecular and molecular interactions stabilizing metal-oxygen cores and many others. This paper reports the synthesis and characterization of new lithium [Li4(OSiPh3)4(THF)2] (1), and sodium [Na4(OSiPh3)4] (2) species, which were later used in obtaining novel gadolinium [Gd(OSiPh3)3(THF)3]·THF (3), and erbium [Er(OSiPh3)3(THF)3]·THF (4) configuration, it can result in res were determined for all 1–4 compounds, and in addition, IR, Raman, absorption spectroscopy studies were conducted for 3 and 4 lanthanide compounds. Furthermore, direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 3 and 4 were carried out in the temperature range 1.8–300 K. The 3 shows behavior characteristics for the paramagnetism of the Gd3+ ion. In contrast, the magnetic properties of 4 are dominated by the crystal field effect on the Er3+ ion, masking the magnetic interaction between magnetic centers of neighboring molecules.

Copper(II) complexes of 1,3-dimethyl-5-(4′/3′-pyridylazo)-6-aminouracil: Structures, redox, magnetic and protein binding properties

Two new monomeric copper(II) complexes based on 1,3-dimethyl-5-(4′/3′-pyridylazo)-6-aminouracil (HL1: 4′-pyridylazo, complex 1: cis-CuIIL12.MeOH; HL2: 3′-pyridylazo, complex 2: cis-CuIIL12.H2O) were synthesized, characterized and investigated for redox, magnetic and protein-binding properties. The complex 1 is in monoclinic space group C2/c, Z = 4 whereas the complex 2 is in triclinic space group P-1, Z = 2. The complexes hold similar structure in solid and solution state as could be infered from the EPR spectra of 1 having well-resolved hyperfine features, g|| > g┴ > ge (g|| =2.20 and g┴ =2.05). The E½ values for oxidative response of Cu(III)/Cu(II) couple are 1.030 V (ΔE = 133 mV) for 1 and 0.982 V (ΔE = 128 mV) for 2, indicating high redox stability of Cu(II) ions in the complex environment. Direct current (DC) variable-temperature magnetic susceptibility measurements on polycrystalline sample of 1 were carried out in the temperature range 1.8-300 K. The magnetic behavior indicates a weak antiferromagnetic interaction between Cu(II) ions in the crystal lattice below 25 K. The study of Bovin Serum Albumin (BSA)-complex interactions reveals that the BSA binds the complexes through the sites of tryptophan residues in 1:1 manner (n = 0.9007 & KA = 1.482 × 104M−1 for 1 and 0.7433 & KA =2.394×103M−1 for 2). Thus, the developed complexes could be treated as muti-functional materials.

The Importance of Electrical Impedance Spectroscopy and Equivalent Circuit Analysis on Nanoscale Molecular Electronic Devices

AbstractTo understand the electrical and charge transport phenomena in either single or large‐scale molecular junctions, direct current (DC) measurements are mainly utilized. The current–voltage data obtained from DC measurements on molecular junctions (MJs) are employed to infer charge transport parameters, including barrier height, contact resistance, attenuation factor (β), and underlying transport mechanisms. However, DC measurements can not separate the individual electrical components, as it produces a total current that flows in the molecular junctions. Contact resistance obtained from the DC measurements by extrapolating plot of resistance versus chain length can not make exact value. In addition, defected SAMs‐based MJs or junctions having a protective layer, DC measurements alone can predict neither proper electrical values nor the correct transport mechanisms and it lacks frequency response. Electrical impedance spectroscopy (EIS) along with the circuit model enables the identification of individual electrical components of the molecular junctions and faultless contact resistance values that facilitate the model of actual transport mechanisms. In this Review, the working principle of electrical impedance spectroscopy and circuit modeling to digitize the experimental results on various molecular junctions, is discussed. Overall, the EIS technique can serve as an excellent analytical tool for the proper electrical characterization that is highly desirable for molecular electronics.

Calcium-doping effects on structure and electric performances of garnet-type Li6.6La3Zr1.6Sb0.4O12 solid-state electrolytes

In this work, the Li6.6La3-xCaxZr1.6Sb0.4O12 (x = 0, 0.05, 0.1, 0.15, 0.20) ceramic electrolytes were synthesized via solid-state sintering method in air. The effects of amount of calcium substitution on the crystal structure, microstructure, relative density and conductivities of garnet-type Li6.6La3Zr1.6Sb0.4O12 electrolytes were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), Archimedes' method Impedance analysis approach and direct current (DC) polarization measurement, respectively. Results confirmed that suitable amount of Ca doping in Li6.6La3Zr1.6Sb0.4O12 sample can accelerate densification and enhance the lithium-ion conductivity. Particularly, Li6.65La2.95Ca0.05Zr1.6Sb0.4O12 ceramics exhibits the maximum relative densities of 94.3% and total room-temperature Li-ion conductivity of 8.95 × 10−4 S·cm−1, along with the minimum activation energy of 0.37 eV. Additionally, the assembled symmetrical batteries Li/Li6.65La2.95Ca0.05Zr1.6Sb0.4O12/Li are cycled galvanostatically under the current densities of 0.02, 0.05 and 0.10 mA·cm−2, respectively, showing the flat voltage plateau and the small polarization voltage, indicating the excellent lithium dissolution/deposition cycling performance.

Peculiarities of specular infrared reflection spectra of ZnO-based ceramics

Undoped and Mn-doped ZnO ceramics were theoretically and experimentally investigated using specular infrared reflection method. It was shown that infrared reflection spectra can be modeled using the parameters explored for ZnO single crystals. For ceramic samples, it was shown that ZnO grains with orientation of the C-axis along the normal to the electric field ( ) give the main contribution to IR reflection spectra. It has been ascertained that the surface roughness is manifested in these spectra mainly within the range 450…550 cm–1 giving negligible effect for the frequencies above longitudinal phonon frequency. This allowed the electrophysical parameters of ZnO crystallites to be evaluated. In the case of undoped ceramics, the obtained results were found to be consistent with the values of direct current measurements. This finding supports the utility of infrared spectroscopy for determination of the electrophysical parameters of polycrystalline ceramic materials. For Mn-doped ceramic samples, the conductivity value measured using the direct current method was found to be essentially lower than those determined from simulation of infrared reflection spectra. This phenomenon was explained by barrier formation at the grain boundaries in Mn-doped ZnO ceramics.

Thermal, Morphological, Electrical Properties and Touch-Sensor Application of Conductive Carbon Black-Filled Polyamide Composites

Polyamide 66 (PA66) is a well-known engineering thermoplastic polymer, primarily employed in polymer composites with fillers and additives of different nature and dimensionality (1D, 2D and 3D) used as alternatives to metals in various technological applications. In this work, carbon black (CB), a conductive nanofiller, was used to reinforce the PA66 polymer in the 9–27 wt. % CB loading range. The reason for choosing CB was intrinsically associated with its nature: a nanostructured carbon filler, whose agglomeration characteristics affect the electrical properties of the polymer composites. Crystallinity, phase composition, thermal behaviour, morphology, microstructure, and electrical conductivity, which are all properties engendered by nanofiller dispersion in the polymer, were investigated using thermal analyses (thermogravimetry and differential scanning calorimetry), microscopies (scanning electron and atomic force microscopies), and electrical conductivity measurements. Interestingly, direct current (DC) electrical measurements and conductive-AFM mapping through the samples enable visualization of the percolation paths and the ability of CB nanoparticles to form aggregates that work as conductive electrical pathways beyond the electrical percolation threshold. This finding provides the opportunities to investigate the degree of filler dispersion occurring during the transformation processes, while the results of the electrical properties also contribute to enabling the use of such conductive composites in sensor and device applications. In this regard, the results presented in this paper provide evidence that conductive carbon-filled polymer composites can work as touch sensors when they are connected with conventional low-power electronics and controlled by inexpensive and commercially available microcontrollers.

Importance of impedance spectroscopy in self-assembled monolayer-based large-area tunnel junctions

Two-terminal direct current (DC) measurements are generally used for the electrical characterization of self-assembled monolayer (SAM)-based large-area tunnel junctions. In DC measurements, the total current through the molecular junction is measured and it is thus impossible to separate molecular effects from interface effects. The charge transport parameters are derived indirectly from the current–voltage relationship. For instance, contact resistance at the interface between the electrode and SAMs is estimated by extrapolating the resistance versus chain length curve. On the other hand, through impedance spectroscopy along with equivalent circuit modelling, each component of the junction can be determined. This paper compares the contact resistance values estimated using both DC and impedance spectroscopic data of alkanethiolate SAM-based molecular junctions reported previously. We show that in the case of molecular tunnel junctions with a resistive protective layer (PL), the widely used DC measurements alone fail to show the actual molecular behaviour of the junction as the charge transport through the junction is dominated by the PL itself. We also show that contact resistance estimated from the DC measurements on defective SAM junctions can be wrong and leads to the incorrect transport mechanism, while the impedance measurements estimate the actual values of contact resistance and identify the bottlenecks in charge transport through such a defective molecular junction.

Unusual Cross‐Shelf Transport Driven by the Changes of Wind Pattern in a Marginal Sea

AbstractThe traditional understanding of the regional circulation in the Northwest Pacific marginal seas is that the Korean Coastal Current flows southward, following the isobaths of 20–50 m. However, an unusual tongue‐shaped structure of cold water is observed in satellite SST data in January 2017, indicating a possible offshore spread of cold coastal water into the middle Southern Yellow Sea (SYS). Additional observations, including in situ hydrographic data as well as direct current measurement, also suggest this cross‐shelf transport of the Korean Coastal Water in January 2017. Our analysis shows that this flow breaks through the isobaths at ∼37°N, moves southward between 50–75 m, and eventually veers anti‐cyclonically at ∼35°N to join the western slope of the SYS. This circulation pattern is further supported by heat budget analysis. Diagnosis of potential vorticity (PV) reveals that the elevated negative PV anomaly imposed by surface wind stress favors this unusual cross‐shelf transport. The change of wind pattern, although under a deceasing wind speed condition, plays an important role. This work provides an alternative view of the wintertime circulation pattern and motivates future studies of the variability of the coastal currents over interannual and longer time scales in the SYS.

Measurement of Polarization Resistances of LSCF/YSZ/LSCF Symmetrical Cell Using Alternating Current (AC) and Direct Current (DC) Techniques

Solid oxide fuel cells (SOFCs) are electrochemical devices, which can efficiently convert the chemical energy stored in fuels such as CH4 and H2 to electrical energy. SOFCs are of great significance for the next generation of clean energy storage and conversion. Yttria stabilized zirconia (YSZ) is a common solid oxide electrolyte used in SOFCs since it has outstanding oxygen ion conductivity, especially when operated at a high temperature (>800°C). Lanthanum strontium cobalt iron oxide (LSCF) is a mixed ionic-electronic conductor (MIEC), which offers both good electronic conductivity and good oxygen ion conductivity. Electrochemical impedance spectroscopy (EIS) is typically used to study the electrochemical performance of SOFCs. However, when using the common two-electrode EIS, the electrode processes at the cathode and anode cannot be studied separately. To study the electrode processes at the cathode and anode, a three-electrode EIS (two-electrode EIS with one pseudo-reference electrode) was performed on an LSCF/YSZ/LSCF bar-shaped symmetrical cell with platinum strip electrodes as probes. The point-by-point sum of the EIS spectra across the cathode and probe and across the anode and probe was found to match the impedance across the cathode and the anode. Also, polarity was switched, and it was found that the two electrodes do not necessarily have identical polarization resistance. Direct current (DC) measurements were also used to measure the polarization resistance of two electrodes separately with good agreement with the EIS results.

From δl- to δT c-pinning in CaKFe4As4 single crystals obtained by adjusting their defect structures

We have investigated the vortices pinning behaviors of CaKFe4As4 with two types of defect structures by alternating current and direct current susceptibility measurements under the Ginzburg-Landau theory and collective pinning model. We observed a new dissipative peak at temperature T J in each out-of-phase () curve even at low magnetic field in the samples with thick CaFe2As2 intercalations, which has been ascribed to the weak Josephson-like link. The unrelaxed current J c and the normalized pinning energy g(t) have been investigated for both types of the CaKFe4As4 crystals based on the dynamic relaxation rate Q and transient current J s by means of generalized inversion scheme. For the samples with monolayer-KFe2As2 intercalations, the temperature dependence of J c and g(t) is found to be in agreement well with the model of single vortex δT c-pinning. But for the samples with thick CaFe2As2 intergrowths, both the δT c- and δl-pinning are in functioning at low magnetic field, but the δl pinning will play a leading role at magnetic field above 3.0 T. Differential charge analysis shows that the intergrowth of KFe2As2 should be normal phase and the CaFe2As2 will become superconducting one due to the charge transfer. The non-superconducting KFe2As2 will induce an abruptly spatial change of T c resulting to strong δT c-pinning, and the superconducting CaFe2As2 phase can mainly cause to fluctuate of mean free path leading to δl-pinning. The present work illustrates how the defect structure affects the flux pinning behaviors and can provide a new clue to design high-performance superconducting wire/tapes and films for strong magnetic field applications.

Measurement of Polarization Resistances of LSCF/YSZ/LSCF Symmetrical Cell Using Alternating Current (AC) and Direct Current (DC) Techniques

Lanthanum strontium cobalt iron oxide (LSCF) is a promising mixed ionic-electronic conductor (MIEC) used in solid oxide fuel cells (SOFCs) as electrodes. Symmetrical cells are usually used for study the electrode kinetics in the SOFCs. However, the polarization resistance and the electrode performance on the typical LSCF/YSZ/LSCF disk-shaped cell cannot be studied separately by using the typical two-electrode electrochemical impedance spectroscopy (EIS). Thus, two-electrode EIS with one pseudo-reference electrode needs to be used to study the two electrodes separately. Also, LSCF/YSZ/LSCF bar-shaped sample needs to be made so that platinum strip electrodes can be applied along the length of the YSZ bar for EIS testing. Since SOFCs are usually operated in DC mode, DC measurements also need to be performed to study the electrode polarization resistance and electrode performance. In this study, an LSCF/YSZ/LSCF bar-shaped symmetrical sample was made to measure the electrode polarization resistances of the two electrodes separately using both EIS and DC techniques. Results show that the two electrodes need not be identical. EIS and DC results are in good agreement with each other.