Measurements Of Electrical Properties Research Articles

Understanding the correlation between intermediate monoclinic phase (Cc) and piezoelectric properties in NaNbO3-BaTiO3-CaZrO3 ternary system with octahedral tilt

Compared with traditional tetragonal (T) P4mm - rhombohedral (R) R3m morphotropic phase boundary (MPB) system, the structure-property relationship of MPB systems with octahedral tilt is still unclear. In this work, the phase structure evolution under composition and electric field modulations in lead-free (0.9-x)NaNbO3-0.1BaTiO3-xCaZrO3 (NN-BT-xCZ) close to the untilt P4mm-tilt R3c MPB was investigated in details by means of the ex- and in-situ x-ray diffraction and various electrical property measurements. Both P4 mm and R3c phases can irreversibly transform into a Cc phase under electric field loading, which should be considered as a result of the cooperative coupling between ferroelectric and antiferrodistortive instabilities. Quantitative analysis indicates that little composition dependent lattice strain and domain switching of P4 mm phase can be observed, and the variation of piezoelectric coefficient is closely related to Cc phase, which exhibits an enhancement of both lattice strain and domain switching within MPB. This suggests that lattice strain and domain switching of Cc phase are coupled. On the contrary, both of them are competed in P4 mm phase because the P4 mm phase is dominated by irreversible domain switching. The experimental results would benefit for deeply understanding the origin of piezoelectric response for many octahedral-tilt MPB piezoelectric systems.

Long-Time Magnetic Relaxation in Antiferromagnetic Topological Material EuCd2As2 Supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300600 and 2018YFA0305600), the National Natural Science Foundation of China (Grant No. 11974404), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB33000000), and the Youth Innovation Promotion Association of CAS (Grant No. 2017013).

Magnetic topological materials have attracted much attention due to the correlation between topology and magnetism. Recent studies suggest that EuCd2As2 is an antiferromagnetic topological material. Here by carrying out thorough magnetic, electrical and thermodynamic property measurements, we discover a long-time relaxation of the magnetic susceptibility in EuCd2As2. The (001) in-plane magnetic susceptibility at 5 K is found to continuously increase up to ∼10% over the time of ∼14 hours. The magnetic relaxation is anisotropic and strongly depends on the temperature and the applied magnetic field. These results will stimulate further theoretical and experimental studies to understand the origin of the relaxation process and its effect on the electronic structure and physical properties of the magnetic topological materials.

Measurement of Electrical Properties of Superconducting YBCO Thin Films in the VHF Range.

A new measurement technique of electrical parameters of superconducting thin films at the Very High Frequency (VHF) range is described, based on resonators with microstrip (MS) structures. The design of an optimal resonator was achieved, based on a thorough theoretical analysis, which is required for derivation of the exact configuration of the MS. A theoretical model is presented, from which an expression for the attenuation of a MS line can be derived. Accordingly, simulations were performed, and an optimal resonator for the VHF range was designed and implemented. Production constraints of YBa2Cu3O7 (YBCO) limited the diameter of the sapphire substrate to 3″. Therefore, a meander configuration was formed to fit the long λ/4 MS line on the wafer. By measuring the complex input reflection coefficients of a λ/4 resonator, we extracted the quality factor, which is mainly affected by the dielectric and conductor attenuations. The experimental results are well fitted by the theoretical model. The dielectric attenuation was calculated using the quasi-static analysis of the MS line. An identical copper resonator was produced and measured to compare the properties of the YBCO resonator in reference to the copper one. A quality factor of ~ was calculated for the YBCO resonator, three orders of magnitude larger than that of the copper resonator. The attenuation per unit length of the YBCO layer was smaller by more than five orders of magnitude than that of the copper.

Field-insensitive giant dynamic piezoelectric response and its structural origin in (Ba,Ca)(Ti,Zr)O3 tetragonal-orthorhombic phase-boundary ceramics

BaTiO3 (BT)-based ceramics usually exhibit superior quasi-static piezoelectric response but relatively low electrostrain, which limits their actuator applications. In this study, lead-free (Ba0.835+xCa0.165-x)(Ti0.91Zr0.09)O3 (x = 0–0.06) (BaxCTZ) ceramics with the compositions close to the tetragonal (T)-rich side of orthorhombic (O)-T polymorphic phase boundary (PPB) were reported to exhibit a field insensitive giant dynamic piezoelectric response (d33* >1050 pm/V) over a wide electric field range up to 2 kV/mm, resulting in the large strain value of ∼0.21 %. Detailed structural investigations combined with various electrical properties measurements reveal that the superior dynamic piezoelectric response is attributed to the combination of piezoelectric effect and domain switching behavior due to the chemical modulated O-T PPB, and the field induced partially irreversible T-O phase transition. The results demonstrate that the studied compositions have great potential for applications of lead-free actuator piezoceramics.

Pressure-induced superconductivity and modification of Fermi surface in type-II Weyl semimetal NbIrTe4

Weyl semimetals (WSMs) hosting Weyl points (WPs) with different chiralities attract great interest as an object to study chirality-related physical properties, topological phase transitions, and topological superconductivity. Quantum oscillation measurements and theoretical calculations imply that the type-II WPs in NbIrTe4 are robust against the shift of chemical potential making it a good material for pressure studies on topological properties. Here we report the results of electrical transport property measurements and Raman spectroscopy studies under pressures up to 65.5 GPa accompanied by theoretical electronic structure calculations. Hall resistivity data reveal an electronic transition indicated by a change of the charge carrier from multiband character to hole-type at ~12 GPa, in agreement with the calculated Fermi surface. An onset of superconducting transition is observed at pressures above 39 GPa, with critical temperature increasing as pressure increases. Moreover, theoretical calculations indicate that WPs persist up to highly reduced unit cell volume (−17%), manifesting that NbIrTe4 is a candidate of topological superconductor.

Insight into influence of thermodynamic coefficients on transient negative capacitance in Zr-doped HfO2 ferroelectric capacitors* *Project supported by the National Key Project of Science and Technology of China (Grant No. 2017ZX02315001-002).

We study the influence of the thermodynamic coefficients on transient negative capacitance for the Zr-doped HfO2 (HZO) ferroelectric capacitors by the theoretical simulation based on the Landau–Khalatnikov (L-K) theory and experimental measurement of electrical properties in the resistor-ferroelectric capacitor (R-FEC) circuit. Our results show that the thermodynamic coefficients α, β and γ also play a key role for the transient NC effect besides the viscosity coefficient and series resistor. Moreover, the smaller coefficients α and β, the more significant the transient NC effect. In addition, we also find that the thermodynamic process of transient NC does not obey the generally accepted viewpoint of Gibbs free energy minimization.

Fast synthesis and improved electrical stability in n-type Ag2Te thermoelectric materials

Cu- and Ag-based superionic conductors are promising thermoelectric materials due to their good electrical properties and intrinsically low thermal conductivity. However, the poor electrical and thermal stability restrict their application. In this work, n-type pure phase Ag2Te compound is synthesized by simply grinding elemental powders at room temperature and compacted by spark plasma sintering. It is found that, because of the migration of Ag+ after the phase transition around 425 K, submicron pores are formed inside the samples during the electrical performance measurement, resulting in poor electrical stability and repeatability of Ag2Te samples. However, Pb-doped Ag2-xPbxTe (x = 0–0.05) specimens exhibit improved electrical stability by the precipitation of the secondary phase PbTe in the Ag2Te matrix, which is confirmed via cyclic electrical property measurement and microstructure characterization. A maximum zT = 0.72 is obtained at 570 K for x = 0.03 mainly due to the increased power factor.

Electrical Resistivity of FeS at High Pressures and Temperatures: Implications of Thermal Transport in the Core of Ganymede

AbstractTerrestrial‐type planetary cores are thought to be predominantly composed of Fe with varying amounts of lighter chemical species or impurities chosen from a narrow range of possible elements, which includes S. These impurity elements may contribute significant effects to the transport properties of these cores, which have direct influence over dynamo and thermal evolution of the planetary body. Recent experimental methods have partially eased the substantial challenges that arise in direct measurements of electrical transport properties at high pressures and temperatures. In this study we show how this methodology can be used to measure the electrical resistivity of a sample in powder form. The electrical resistivity of FeS was measured in both solid and molten states at pressures up to 5 GPa and the thermal conductivity was calculated using the Wiedemann–Franz Law from the electrical measurements. The results showed FeS is notably more electrically and thermally conductive when compared to previous studies in both the solid and molten states. The results were used to estimate the adiabatic conductive heat flow of a molten FeS core model of Ganymede, which showed that thermal convection is permissible as a dynamo power source.

Dielectric Properties of x BiInO₃-(1-x) Pb(Zr₀.₅₂Ti₀.₄₈)O₃ Solid Solutions.

This study focused on the synthesis and electrical property measurements of the lead zirconate titanate (PZT)-bismuth indate (BI) perovskite solid solution system. As the PZT binary system is a very well-developed and integrated materials system, identifying new ternary systems based on PZT would allow for a new dimension of control into the exploration and improvement of its electrical properties, which could enable enhancements in the performance of current technology and devices. Here, the solid solution of BiInO3-PbZrO3-PbTiO3 ( x BI-(1- x ) PZT 52/48) was explored. Through calcination studies, stable solid solutions were obtained, and compositions up to a maximum of 15-mol% BI were synthesized. With increasing BI content, the symmetry transitioned from a tetragonal P4mm phase toward a rhombohedral R3m phase. The Curie temperature of these samples decreased with increasing mol% BI from ~390 °C in pure PZT 52/48 to 322 °C in 10% BI. Ferroelectric and piezoelectric studies of the 2.5% BI sample showed a coercive field of 14.4 kV/cm, [Formula: see text]/cm2, [Formula: see text]/cm2, and a d33∗ = 280 pC/N under a maximum applied field of 70 kV/cm at 1 Hz.

Advanced low damage manufacturing processes to fabricate SOI FinFETs and measurement of electrical properties

In this paper, FinFETs are realized by integrating neutral beam etching(NBE) and microwave annealing (MWA) into the fabrication process. Electrical characteristics are measured at room temperature and parameters such as Sub-threshold swing of 89 mV/decade, Ion/Ioff of 106, DIBL of 72 mV/V and effective mobility (μeff) of 502 cm2V−1 s−1 are obtained with Wfin/Lgate = 40/100 nm. These characteristics are superior by using neutral beam etching than by using RIE-like condition, and the Vt shift at reduced Lgate is also suppressed. A damaged layer at high-k/Si interface by RIE-like condition is observed in the TEM image, which can correspond to the degradation in electrical characteristics. Furthermore, the proportional scaling of Ion versus Wfin indicates negligible S/D resistance due to good activation by Microwave annealing (MWA). In short, functional FinFETs were fabricated by Neutral beam etching (NBE) and Microwave annealing (MWA) for the first time, and these results pave ways for the techniques to be adopted in the advanced semiconductor processing. The SOI FinFETs demonstrate proportional scaling of on current versus the fin width and indicating that the S/D region is well activated by the microwave annealing method.

Non-Fermi liquid behavior and signature of Griffiths phase in Ni–Cr binary alloy

Detailed magnetic, electrical, and thermal property measurements have been carried out on Ni100−xCrx binary alloys, mainly to study the effect of Cr. The following points emerge from this study: with the increase in Cr concentration, magnetic moment and Curie temperature linearly decreased and the ferromagnetic order is completely suppressed at the critical concentration (xcr ≈ 12.16 ± 0.03). The Rhodes–Wohlfarth ratio increases as the concentration approaches xcr, suggesting a weak itinerant ferromagnetic character of NiCr compositions (x < xcr). Analysis of low-temperature electrical resistivity and specific heat data suggests that the spin fluctuation’s contribution increases and the Fermi-liquid behavior breaks down as the concentration approaches xcr. For x ∼ xcr, the dc susceptibility χ(T) deviates from the Curie–Weiss law reminiscent to that of the Griffiths phase. The low-temperature magnetic isotherms of Ni–Cr follow power law, M(H)=M0+dλHλ, and the non-universal exponent (λ) shows a minimum at xcr ∼ 12. Further, temperature dependence of magnetization studies also support the presence of the quantum Griffiths phase, similar to that reported in the Ni–V alloy system. The temperature dependencies of the electrical resistivity, magnetization, and specific heat follow the theoretical predictions of a quantum critical point within experimental uncertainties.

Design of a vane mixer with controlled extensional/shear strength ratio and its application for carbon fiber/polyamide 6 composites

AbstractIn this work, a novel melt mixing method and its corresponding mixing device are developed. The extensional/shear strength ratio of the device can be controlled by adjusting its eccentricity. The structure and working principle of the device are introduced in detail. Carbon fiber (CF)/polyamide 6 (PA6) composites are prepared via this novel mixing device. The influences of eccentricity and mixing time on the morphology, CF length, thermal, mechanical, and electrical properties of CF/PA6 composites are studied. Scanning electron microscopy results show that CFs uniformly disperse in the matrix and interfacial adhesion between CFs and PA6 is improved. It is observed that CF length and its distributions can be optimized by changing eccentricity. The maximum average fiber length is about 351 μm. Differential scanning calorimetry results exhibit that the Xc increases 6.5% when eccentricity is 2 mm. Mechanical test results show tensile strength and modulus increase first and then decrease with the increasing eccentricities or mixing time. Electrical property measurement shows an obvious increase when eccentricity is 2 mm due to good fiber dispersion and long fiber retention length. The experimental results indicate that the novel mixing method and its corresponding apparatus provide an environment‐friendly and effective way to prepare polymer‐based composites.

Electrochemical imaging of contact boundary by using electron-beam addressing of a virtual cathode display

Abstract A scanning electrochemical microscope (SECM) enables surface measurements of electrical properties of various wet samples including living cells, although its probe cannot reach the interface where the samples contact a substrate. This paper reports our innovative method for electrochemical imaging of the contact boundary in wet samples in water solution. We used electron-beam (EB) addressing of a virtual cathode (VC) for an inverted electron beam lithography system, and we carried out imaging of the contact boundaries which cannot be approached by conventional scanning probe microscopes. This VC was formed on the surface of a 100-nm thick silicon nitride (SiN) membrane by low-energy EB irradiation from the lower side of the membrane. The VC appeared at the contact boundary of the wet samples and the membrane; therefore the VC virtually worked at the boundary as the scanning probe of the SECM to observe the wet contact interface. We acquired topographic and electrochemical images of micro polystyrene spheres and a DPPC/TR-DPPE supported lipid bilayer by measuring the probe current in the sample interface. The imaging results suggested spatial resolutions of ∼180 nm width and ∼90 nm depth in a topographical image could be captured using this VC-SECM system.

A two-sensor 3ω-2ω method for thermal boundary resistance measurement

Thermal boundary resistance (TBR), which measures an interface's resistance to the thermal flow, is of critical importance among various areas, such as electronics cooling and thermoelectric materials. As for measuring TBR, electrical techniques are generally less sensitive compared to optical ones, but they are easily operable and compatible with the measurement of other electric properties; thus, it is highly desirable to develop electrical methods with higher accuracy and larger measurement range. Here, a two-sensor 3ω-2ω method with a novel experimental procedure design is proposed, which can well address those deficiencies in the conventional 3ω method. Two parallel metal sensors are fabricated, with one of them being wide and the other being narrow. The temperature changes of these two sensors are measured by detecting the 3ω and 2ω signals, respectively. The measurement includes three steps: (1) obtain thin film's thermal conductivity from the wide sensor's 3ω thermal response; (2) obtain substrate thermal conductivity from the narrow sensor's 2ω thermal response; and (3) derive an effective TBR from the narrow sensor's 3ω thermal response. Moreover, it is found the TBRs of metal/dielectric and dielectric/substrate interfaces are distinguishable due to the considerable difference between their contact areas, which enables us to separate these two TBRs by varying the contact area (heater's width). Then, our method is employed to probe the TBRs between the Al2O3 nanofilm and Si as well as SiC substrates at room temperature and good agreement with the previous measurements is achieved, verifying its feasibility. Our present scheme will be helpful for the experimental study of interfacial thermal transport.

Identification of Brain Damage after Seizures Using an MR-Based Electrical Conductivity Imaging Method.

Previous imaging studies have shown the morphological malformation and the alterations of ionic mobility, water contents, electrical properties, or metabolites in seizure brains. Magnetic resonance electrical properties tomography (MREPT) is a recently developed technique for the measurement of electrical tissue properties with a high frequency that provides cellular information regardless of the cell membrane. In this study, we examined the possibility of MREPT as an applicable technique to detect seizure-induced functional changes in the brain of rats. Ultra-high field (9.4 T) magnetic resonance imaging (MRI) was performed, 2 h, 2 days, and 1 week after the injection of N-methyl-D-aspartate (NMDA; 75 mg/kg). The conductivity images were reconstructed from B1 phase images using a magnetic resonance conductivity imaging (MRCI) toolbox. The high-frequency conductivity was significantly decreased in the hippocampus among various brain regions of NMDA-treated rats. Nissl staining showed shrunken cell bodies and condensed cytoplasm potently at 2 h after NMDA treatment, and neuronal cell loss at all time points in the hippocampus. These results suggest that the reduced electrical conductivity may be associated with seizure-induced neuronal loss in the hippocampus. Magnetic resonance (MR)-based electrical conductivity imaging may be an applicable technique to non-invasively identify brain damage after a seizure.

Comparative measurements and analysis of the mechanical and electrical properties of Ti-Zr-C nanocomposite: Role of stoichiometry

Nanocomposites based on hard compounds are currently on the stage of active research and development. Hence the analysis of a relation between nanostructure and functional properties are of great importance. The main purpose of the study was to assess the stoichiometry effect on the finite characteristics of TiZrC nanocomposite coatings. This paper presents the analysis of the Ti1-xZrxC (x = 0, 0.25, 0.5, 0.75 and 1.0) hard coatings sputtered onto Si substrates by a two-target DC magnetron. It has been found that the increase of carbon content in the bulk of the coatings contributes to the structural changes, namely, lead to the formation of the nc-Ti1-xZrxCy/a-C nanocomposite structure with (Ti,Zr)C solid-solution phase which is in a good agreement to theoretical predictions. Electrical properties measurements have shown infrequent results concerning intrinsic conductivity, which can prosper this system application for a new generation of nano and microsystems. The analysis reveals the nature of tunnelling conductance between the nanoparticles. On the computer simulation of the frequency dependence of the frequency coefficient, three maxima were discovered. Two of them were attributed to dominant phases (Ti1-xZrx)C and amorphous carbon (a-C). The third one is related to the content of another type of nanophase that, due to low content, could not be determined by structural methods. Mechanical tests showed promising results in suitability to micromechanical devices, in particular: sensors, actuators, power-producing devices. These findings establish an understanding of microstructural regularities and enlarge the potential application space for TiZrC-based systems.

Relative permittivity of bioethanol, gasoline and blends as a function of temperature and composition

The dependence of the real part of the relative permittivity of bioethanol, gasoline, and their blends was determined. Measurements were performed in the temperature range between 298 K and 323 K, at a frequency of 100 kHz. Temperature was stabilized within ±0.1K and the uncertainty in the relative permittivity was ±0.01.In all the studied blends, the real part of the relative permittivity decreases as a function of temperature with a very good fit to a linear function. At each temperature, the real part of the relative permittivity increases with the bioethanol content in the sample.The permittivity as a function of blends composition fits very satisfactorily to a fourth - order polynomial. In all cases, the mean square error (ΔRMS) of the permittivity estimation was less than 0.09. Furthermore, for bioethanol concentrations lower than 25%, a second - order polynomial fits with an ΔRMS error below 0.04. At higher bioethanol concentrations, a linear function fits with an ΔRMS error below 0.13.The bioethanol concentration in the blends is estimated from permittivity and temperature measurements, with a mean square error in the estimation of the composition lower than 0.5% in all cases.This work shows that measurements of electrical properties can be very effective in the characterization of gasoline - ethanol blends for laboratory and industrial applications.

Impact of Sn4+ substitution in Mg–Zn ferrites: Deciphering the structural, morphological, dielectric, electrical and magnetic properties

From the viewpoint of enormous applications and research, ferrite materials have already been achieved the status of one of the important branches of materials science. In this report, we have tuned the physical properties of Mg–Zn ferrites by Sn substitution investigated using X-ray diffraction, field emission scanning electron microscopy (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, electrical and dielectric properties and quantum design physical properties measurement system. The Mg0·5Zn0.5SnxFe2-xO4 (0 ≤ x ≤ 0.10) samples have been synthesized by the conventional ceramic technique. The studied ferrites exhibits the single-phase up to x = 0.08 where an increase in lattice constant was observed. The FESEM images revealed the microstructure and the energy dispersive spectroscopy (EDS) confirms the absence of any unwanted elements. The increase (decrease) in bulk density (porosity) was associated with the variation of average grain size. FTIR spectra confirmed the formation of spinel structure. The dielectric polarization or conduction mechanism in these materials is due to the hopping of charge carriers at the octahedral sites. The common dielectric behavior of studied compositions is also observed. The substitution of Sn ions leads to enhanced dielectric constant and ac conductivity due to increased hopping of charge carriers. Complex impedance spectroscopy study revealed the non-Debye type of relaxation process within the studied compositions with a dominant contribution from grain boundary resistance. The dynamic magnetic hysteresis loops are measured to obtain the magnetic parameters. The low values of coercivity revealed the soft magnetic nature of the studied compositions. The obtained saturation magnetization (Ms) for Mg–Zn ferrite (x = 0.00) is comparable with the prior result. Non-linear decrease of Ms (62-44 emu/g) due to Sn substitution is explained based on the variation of magnetic moments over A- and B-sites. The squareness ratio (Mr/Ms) revealed that the magneto-statical interaction is present within the synthesized samples. The constant value of initial permeability (μʹ) over a wide range of frequencies revealed the compositional stability and quality of the prepared ferrite. The variation of μʹ with Sn content is similar to that of Msvs Sn contents. Moreover, theoretical cation distribution and the effect of Sn substitution on the related parameters have also been studied. The studied parameters are compared with the reported results, where available.

Single GaN Nanowires for Extremely High Current Commutation

An array of GaN nanowires (NWs) on Si substrate is synthesized by molecular beam epitaxy. Measurements of electrical properties at room temperature of single NWs transferred to an auxiliary substrate demonstrate that the current density reaches an extremely high level of 2 MA cm−2 without NW damage. Taking into account the limited conductivity of the NW periphery due to electron surface states, that is, the conduction channel narrowing, the effective current density can reach 3 MA cm−2.

Sub-10nm spatial resolution for electrical properties measurements using bimodal excitation in electric force microscopy.

We demonstrate that under ambient and humidity-controlled conditions, operation of bimodal excitation single-scan electric force microscopy with no electrical feedback loop increases the spatial resolution of surface electrical property measurements down to the 5nm limit. This technical improvement is featured on epitaxial graphene layers on SiC, which is used as a model sample. The experimental conditions developed to achieve such resolution are discussed and linked to the stable imaging achieved using the proposed method. The application of the herein reported method is achieved without the need to apply DC bias voltages, which benefits specimens that are highly sensitive to polarization. Besides, it allows the simultaneous parallel acquisition of surface electrical properties (such as contact potential difference) at the same scanning rate as in amplitude modulation atomic force microscopy (AFM) topography measurements. This makes it attractive for applications in high scanning speed AFM experiments in various fields for material screening and metrology of semiconductor systems.