Measurements Of Transport Properties Research Articles

Long-Range Cationic Order Collapse Triggered by S/Cl Mixed-Anion Occupancy Yields Enhanced Thermoelectric Properties in Cu5Sn2S7

To investigate pathways to adjust the charge carrier concentration and optimize the thermoelectric properties, we characterized structural properties, thermal stability, and thermoelectric performance of pristine and Cl-doped Cu5+εSn2−εS7. We demonstrate that Cl doping in Cu5Sn2S7-type monoclinic compounds induces a collapse of the long-range cationic ordering, ultimately leading to a sphalerite-type cubic phase characterized by ordered [Sn(S,Cl)4]x clusters. The change in crystal structure symmetry upon Cl doping is analyzed by Rietveld refinements against X-ray powder diffraction data, transmission electron microscopy, Mössbauer and X-ray absorption spectroscopy, and low- and high-temperature transport property measurements. The thermoelectric properties of the so-obtained cubic sphalerite Cu5+εSn2−εS7–yCly (0 ≤ ε ≤ 0.133, y = 0.35, 0.70) are strongly enhanced with respect to the undoped Cu5Sn2S7: the power factor improves slightly while both electronic and lattice contributions to the thermal conductivity are reduced. Overall, single-phase Cl-doped Cu5.133Sn1.866S7–yCly (y = 0.35, 0.70) compounds exhibit high thermoelectric performance, reaching a maximum ZT of 0.45 at 670 K.

Discovery of Two Families of Vsb-Based Compounds with V-Kagome LatticeSupported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0304700 and 2018YFE0202601), the National Natural Science Foundation of China (Grant Nos. 51922105, 51772322, 52025025, and 52072400), and the Beijing Natural Science Foundation (Grant No. Z200005).

We report the structure and physical properties of two newly discovered compounds AV8Sb12 and AV6Sb6 (A = Cs, Rb), which have C 2 (space group: Cmmm) and C 3 (space group: ) symmetry, respectively. The basic V-kagome unit appears in both compounds, but stacking differently. A V2Sb2 layer is sandwiched between two V3Sb5 layers in AV8Sb12, altering the V-kagome lattice and lowering the symmetry of kagome layer from hexagonal to orthorhombic. In AV6Sb6, the building block is a more complex slab made up of two half-V3Sb5 layers that are intercalated by Cs cations along the c-axis. Transport property measurements demonstrate that both compounds are nonmagnetic metals, with carrier concentrations at around 1021 cm−3. No superconductivity has been observed in CsV8Sb12 above 0.3 K under in situ pressure up to 46 GPa. Compared to CsV3Sb5, theoretical calculations and angle-resolved photoemission spectroscopy reveal a quasi-two-dimensional electronic structure in CsV8Sb12 with C 2 symmetry and no van Hove singularities near the Fermi level. Our findings will stimulate more research into V-based kagome quantum materials.

Local-Disorder-Induced Low Thermal Conductivity in Degenerate Semiconductor Cu22Sn10S32.

S-based semiconductors are attracting attention as environmentally friendly materials for energy-conversion applications because of their structural complexity and chemical flexibility. Here, we show that the delicate interplay between the chemical composition and cationic order/disorder allows one to stabilize a new sphalerite derivative phase of cubic symmetry in the Cu-Sn-S diagram: Cu22Sn10S32. Interestingly, its crystal structure is characterized by a semiordered cationic distribution, with the Cu-Sn disorder being localized on one crystallographic site in a long-range-ordered matrix. The origin of the partial disorder and its influence on the electronic and thermal transport properties are addressed in detail using a combination of synchrotron X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy, theoretical modeling, and transport property measurements. These measurements evidence that this compound behaves as a pseudogap, degenerate p-type material with very low lattice thermal conductivity (0.5 W m-1 K-1 at 700 K). We show that localized disorder is very effective in lowering κL without compromising the integrity of the conductive framework. Substituting pentavalent Sb for tetravalent Sn is exploited to lower the hole concentration and doubles the thermoelectric figure of merit ZT to 0.55 at 700 K with respect to the pristine compound. The discovery of this semiordered cubic sphalerite derivative Cu22Sn10S32 furthers the understanding of the structure-property relationships in the Cu-Sn-S system and more generally in ternary and quaternary Cu-based systems.

Origin of large magnetoresistance in the topological nonsymmorphic semimetal TaSe3

$\mathrm{Ta}{\mathrm{Se}}_{3}$ is a layered van der Waals semimetal with several inverted band gaps throughout the entire Brillouin zone and nontrivial ${Z}_{2}$ topological indices, which place it at the boundary between a strong and a weak topological phase. Our transport experiments reveal a quadratic nonsaturating magnetoresistance (MR) with values reaching ${10}^{4}$% at 1.8 K and 14 T, whose origins have to be searched in the material's band structure. Here we combine angle-resolved photoelectron spectroscopy experiments, also with spin resolution, with ab initio calculations based on density functional theory in order to draw a connection between the Fermi surface topology and the measured transport properties. Simulations based on the calculated Fermi surface clarify that electron-hole compensation plays an important role for the observed MR in the bulk material. At the surface, the position of Fermi level differs, and it can be controlled by alkali metal deposition which accounts not only for the energy shift of the bands but it slightly modifies the dispersion of the valence and conduction bands. We propose that the observed band-gap renormalization might offer a route for engineering the topological phase in $\mathrm{Ta}{\mathrm{Se}}_{3}$, alternative to strain.

Electrochemical Methods for the Study of Liquid Metals: Highlights from Metallurgical Transactions

Metallurgical Transactions—and its subsequent MMTA and MMTB—has been a home for numerous contributions related to electrochemistry as it applies to solid, but also liquid materials. Herein, a perspective is presented to highlight the utility of electrochemical methods as applied to the study of liquid metals. The review of a subset of papers shows the diversity of experimental options available to investigate the thermodynamic properties of liquid metals, as well as certain limitations. A specific set of results covering the entire range of two liquid binary systems is reviewed as an illustration of the static electrochemical potential difference method. More recent developments offered by dynamic electrochemical potential methods, using direct and alternating currents or containerless configurations, are reviewed. Advances in electrochemical studies of liquid metals bring the prospect of simultaneous thermodynamic and transport properties measurements closer to reality.

Permselectivity of ionene-based, Aemion® anion exchange membranes

This work reports the permselectivity of an ionene-based anion exchange membrane – ionenes are a class of polymer in which cationic charged groups are located directly on the polymer backbone, as opposed to being pendant. The ionone studied, in the form of commercially available Aemion® anion exchange membranes, is based on hexamethyl-p-terphenyl poly (bibenzimidazolium) (HMT-PMBI), which has been explored in several electrochemical devices, yet their transport numbers, permselectivity, and through-plane conductivity, have not been reported. Measurement of transport properties was carried out on membranes (AF1-HNN8-25, AF1-HNN8-50, AF1-HNN5-25, AF1-HNN5-50) of varying ion exchange capacity and thickness, using the static method in which inherent experimental errors due to liquid junction potentials were elucidated and circumvented. Permselectivity, area specific conductance, and conductivity of Aemion® AEMs are correlated using their fixed charge group concentration. Due to its low water content and high fixed group concentration, the permselectivity of AF1-HNN5-X is higher than AF1-HNN8-X AEMs, despite the latter's higher IEC, but its ionic resistance is lower. Thicker AEMs were confirmed to be more permselective, which can be explained by their relatively lower water content and consequently higher fixed charge group concentration. The permselectivity, area specific conductance, and permselectivity to resistance ratio (α/R) of Aemion® AF1-HNN5-50 were found to be comparable to Selemion AMV, a common anion exchange membrane. The permselectivity/resistance (α/R) value of AF1-HNN8-25 was three times higher than Selemion AMV by virtue of its high ionic conductance.

Aerosol jet printed 3 omega sensors for thermal conductivity measurement.

The 3 omega (3ω) method is a trusted technique for measuring thermal conductivity-a fundamental material property of critical importance in a broad range of applications. However, traditional 3ω sensor processing requires some form of physical vapor deposition, such as metal evaporation or sputtering. These 3ω sensor deposition techniques limit the materials and sample sizes applicable to the 3ω method. This work demonstrates an aerosol jet printing method to directly printsilver 3ω sensors that yield accurate temperature-dependent measurement up to 300°C on materials with thermal conductivity ranging from 1 to 150 W/m K. The interrelationship between printed sensor geometry, sensor thermal stability, and applicability to the 3ω method is examined. Thermal conductivity measurement with 3ω sensors conventionally sintered at 300°C agrees to independent laser flash measurement within 4% from room temperature to 150°C. An unconventional rapid high-temperature sintering method is shown to produce sensors that agree within 3% of the laser flash measurements from room temperature to 300°C. The rapid sintering profiles also reduced the sensor-substrate thermal boundary resistance of the printed sensors by as much as 88%. The direct printing of 3ω sensors creates opportunities for measurement of thermal transport properties in applications previously inapplicable to the 3ω method.

Generation of 30 kbar hydrostatic pressure in Bi2Te3 thin films by uniaxial deformation and its effect on the band structure

Generation of ultrahigh hydrostatic pressure by application of a strong one-axis deformation is demonstrated in epitaxial ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ films on a mica substrate. This was followed by measurements of transport properties in $n$-type ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ as a function of temperature (100--300 K) and pressure of up to 30 kbar. This pressure allowed studies of the restructuring of the conduction band. The nonmonotonic pressure dependence of the Hall coefficient and the increase of electrical conductivity \ensuremath{\sigma}($P$) can only be explained using two subband structures in the conduction band: subbands of light and heavy electrons with a mobility ratio of 10. The gap between the electron subbands increases with the hydrostatic pressure.

Durability of an UHPC containing spent equilibrium catalyst

UHPC is an advanced cementitious material able to meet the current construction industry challenges regarding structural safety and durability. However, new UHPC formulations with limited shrinkage are still being pursued to reduce residual tensile stresses in the UHPFRC layers, for rehabilitation/strengthening applications. This investigation estimates the durability of a non-proprietary UHPC incorporating a by-product originated by the oil refinery industry (ECat), as an internal curing agent. Direct and indirect transport properties measurements as well as the carbonation assessment and evaluation of dimensional resilience to potential deleterious reactions revealed that the new UHPC possesses an excellent durability performance, typical of these materials. These results combined with its self-compacting ability, low autogenous shrinkage and high compressive strength confirm the belief in the role of this new UHPC towards a high-tech construction.

Fine-grained polycrystalline MoTe2 with enhanced thermoelectric properties through iodine doping

Consisting of heavy elements and favorable electronic structure, MoTe2 has great potential as a good thermoelectric material for heat-to-electricity conversion. While some experimental work has been performed on the p-type version, n-type MoTe2 is theoretically predicted to have a great conversion efficiency and is crucial for eventual device functionality, yet has not been explored. Here, the preparation and thermoelectric properties of n-type iodine-doped nano-polycrystalline MoTe2 are currently reported. Nano-polycrystalline MoTe2 − xIx is obtained by ball milling and spark plasma sintering techniques. The composition, morphology and crystal structure of the prepared materials were analyzed by XRD and FESEM, which indicated a homogeneous single phase. The measured transport properties over the temperature range of 298–823 K indicate that iodine doping greatly enhances the carrier concentration and corresponding power factor, and drastically reducing the thermal conductivity. The ECR (Electrical conductivity ratios) carrier scattering analysis demonstrates that dislocation scattering is the main mechanism throughout the experimental temperature range. With the temperature and doping increasing, the thermal conductivity was reduced rapidly, and the minimum value was 1.19 Wm− 1 K− 1 at 673 K. The maximum value of the figure merit ZT ~ 0.16 over 673–750 K, which is much higher than other reported values. These excellent properties imply that MoTe2 will be an efficient candidate for thermoelectric applications.

Effect of Gold Nanoparticles on Transport Properties of the Protic Ionic Liquid Propylammonium Nitrate

Here, we analyze the effect of gold-nanoparticle (AuNPs)-doping of the protic ionic liquid (IL) propyl ammonium nitrate (PAN) on some physical properties, such as density, viscosity, and ionic conductivity, in a broad temperature range. This IL was lightly doped with four different AuNPs (concentration of gold lower than 0.2 mM): Au nanospheres of about 15, 60, and 80 nm diameter and Au nanorods of about 40 nm length and 12 nm width. AuNPs were synthesized following a seed growth approach and further functionalized with O-[2-(3-mercapto propionylamino)ethyl] O′-methyl-poly(ethylene glycol) (m-PEG-SH) in order to provide stability to the IL medium. The stability of the AuNPs in PAN was characterized by UV–vis spectroscopy. The results obtained here indicate that their presence produces a strong influence on the measured transport properties of PAN, decreasing viscosity up to 25% and increasing ionic conductivity up to 10% for the smallest AuNPs. Moreover, as temperature increases, the influence of AuNPs produces a decrease in the percentage deviations for viscosity and ionic conductivity. In the case of density, the AuNP-doping produces a mainly unexpected increase only for the sample with the smallest AuNPs, that is practically constant with temperature. When we equalize the AuNP concentration for all sizes and shapes, it is observed that the smallest AuNPs give higher variations in the studied properties than the bigger ones; also, the shape of the rod has an influence on the measured results. In addition, we have applied Walden’s rule to relate the three measured magnitudes, observing that AuNP addition decreases ionicity with respect to the reference sample, which is even more when we added smaller AuNPs. Finally, we explain all data assuming cation solvation of the AuNPs, which creates a local breaking of the pseudolattice structure of the PAN. Comparison with other published data is difficult because the behavior of a nanoparticle solution strongly depends on its particular composition and no data are available, in our knowledge, of any similar mixture to those studied here.

Residual oxygen driven defect mediated room temperature magnetism in dilute nitrogen incorporated amorphous Al-N-O alloy thin film

In the present work, the effect of residual oxygen during reactive sputtering of Al target in a dilute nitrogen environment has been investigated. We have deposited a thin film by reactive sputtering of high purity Al target (99.999%) using a mixture of ultra-high pure Ar & N2 gas in a percentage ratio of 95% and 5%, respectively. The characterization of as-deposited film using Grazing Incidence X-ray Diffraction (GIXRD), X-ray Photoelectron Spectroscopy (XPS), and Energy-Dispersive X-ray (EDX) spectroscopy reveals that in dilute nitrogen environment Al preferred to react with residual oxygen to form amorphous Al2O3 (a-Al2O3) along with aluminum vacancies (AlV). The dilute nitrogen incorporated in the film occupies the AlV sites in Al2O3 and bonded with nearby oxygen to form Al(NOy)x phase. The bulk of the film mainly consists of Al(NOy)x phase, which decreases as we move towards the film surface. At close to the film surface the oxygen vacancies are significantly present. Magnetic and electrical transport properties measurement of the film shows room temperature (RT) magnetism along with n-type semiconducting behaviour. The origin of RT magnetism and observed transport properties have been investigated using a first-principle calculation based on density functional theory (DFT). The residual oxygen driven defects present in the film are found to play a critical role and discussed in detail. The current study is significant in the sense that it provides a new insight to explore the potentials of Al-N-O alloy-based materials as an n-type magnetic semiconductor at room temperature by manipulating defects and optimizing nitrogen concentration.

Magnetic field controllable planar Hall effect in Sr2IrO4 films

The planar Hall effect (PHE) has remarkable advantages for applications to spintronic devices and the study of intrinsic magnetic properties because of its high signal-to-noise ratio and low thermal drift. Here, the magnetic field controllable PHE in ${\mathrm{Sr}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}/\mathrm{SrTi}{\mathrm{O}}_{3}$ (001) films is presented. The PHE transforms from a ``sinusoidal-shaped'' twofold symmetry to fourfold oscillations with decrease in the magnetic field at 35 K. Furthermore, the PHE is approximately two to three orders of magnitude larger than the giant PHE associated with ferromagnetic semiconductors as the temperature decreases. Based on subsequent measurements of the magnetic transport properties and calculations of the angle between the magnetization and current, the unexpected fourfold-symmetric PHE can be attributed to magnetocrystalline anisotropy and spin-orbital coupling. These observations of PHE facilitate a deeper understanding of the magnetic interactions in ${\mathrm{Sr}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ films and indicate potential applications in spintronic or magnetic-sensor devices.

Thermoelectric Properties of Cu2Se Synthesized by Hydrothermal Method and Densified by SPS Technique.

The aim of the work was to obtain copper (I) selenide Cu2Se material with excellent thermoelectric properties, synthesized using the hydrothermal method and densified by the spark plasma sintering (SPS) method. Chemical and phase composition studies were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods. Measurements of thermoelectric transport properties, i.e., electrical conductivity, the Seebeck coefficient, and thermal conductivity in the temperature range from 300 to 965 K were carried out. Based on these results, the temperature dependence of the thermoelectric figure of merit ZT as a function of temperature was determined. The obtained, very high ZT parameter (ZT~1.75, T = 965 K) is one of the highest obtained so far for undoped Cu2Se.

Oxygen vacancy control of electrical, optical, and magnetic properties of Fe0.05Ti0.95O2 epitaxial films* *Project supported by the National Natural Science Foundation of China (Grant No. 11504192) and the Natural Science Foundation of Shandong Province, China (Grant Nos. ZR201910230017 and BSB2014010).

High-quality Fe-doped TiO2 films are epitaxially grown on MgF2 substrates by pulsed laser deposition. The x-ray diffraction and Raman spectra prove that they are of pure rutile phase. High-resolution transmission electron microscopy (TEM) further demonstrates that the epitaxial relationship between rutile-phased TiO2 and MgF2 substrates is 110 TiO2 ∥ 110 MgF2. The room temperature ferromagnetism is detected by alternative gradient magnetometer. By increasing the ambient oxygen pressure, magnetization shows that it decreases monotonically while absorption edge shows a red shift. The transport property measurement demonstrates a strong correlation between magnetization and carrier concentration. The influence of ambient oxygen pressure on magnetization can be well explained by a modified bound magnetization polarization model.

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.

Weak Kondo effect in the monocrystalline transition metal dichalcogenide ZrTe2

Zr-Te compounds are an ideal platform to investigate novel electrical transport properties. Here we report the Kondo effect in single-crystalline ${\mathrm{ZrTe}}_{2}$. When $T<8$ K, ${\mathrm{ZrTe}}_{2}$ exhibits a $\mathrm{log}T$ dependence of resistivity, which may derive from three different mechanisms, including electron-electron interaction, weak localization, and Kondo effect. By measuring transport properties with magnetic field along different directions, the former two mechanisms were excluded. Isotropic negative magnetoresistance was extracted by subtracting different quadratic background signals caused by Lorentz force, which reveals the existence of a weak Kondo effect in this material.

Iridium valence variation and carrier sign tuning in (Ca,Ba)xLa2−xCuIrO6 double perovskites

We report the structure and properties of ${(\mathrm{Ca},\mathrm{Ba})}_{x}{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{CuIrO}}_{6}$. The rock-salt double perovskite structure goes through a $P\overline{1}$ to $P{2}_{1}/n$ phase transition with increasing Ba content but not with Ca content. In both cases, the Ir ion is oxidized from $4+$ to $5+$ with increasing substitution. Transport and magnetic properties measurements reveal that all compositions are insulating with hysteretic spin-freezing magnetic behavior. Seebeck coefficient measurements reveal a large thermopower change from $+176\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}$/K in ${\mathrm{La}}_{2}{\mathrm{CuIrO}}_{6}$ to $\ensuremath{-}223\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}$/K with increasing Ba content in ${\mathrm{Ba}}_{x}{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{CuIrO}}_{6}$. This behavior is modeled well by the Heikes formula for correlated hopping conduction. ${(\mathrm{Ca},\mathrm{Ba})}_{x}{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{CuIrO}}_{6}$ provides a model system for investigations of other systems with similar carrier sign tuning, with applications toward semiconductors and thermoelectric materials.

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.

Enhancing the Electrochemical Performance and Structural Stability of Ni-Rich Layered Cathode Materials via Dual-Site Doping.

Ni-rich layered cathode materials are considered as promising electrode materials for lithium ion batteries due to their high energy density and low cost. However, the low rate performance and poor electrochemical stability hinder the large-scale application of Ni-rich layered cathodes. In this work, both the rate performance and the structural stability of the Ni-rich layered cathode LiNi0.8Co0.1Mn0.1O2 are significantly improved via the dual-site doping of Nb on both lithium and transition-metal sites, as revealed by neutron diffraction results. The dual-site Nb-doped LiNi0.8Co0.1Mn0.1O2 delivers 202.8 mAh·g-1 with a capacity retention of 81% after 200 electrochemical cycles, which is much higher than that of pristine LiNi0.8Co0.1Mn0.1O2. Moreover, a discharge capacity of 176 mAh·g-1 at 10C rate illustrates its remarkable rate capability. Through in situ X-ray diffraction and electronic transport property measurements, it was demonstrated that the achievement of dual-site doping in the Ni-rich layered cathode can not only suppress the Li/Ni disordering and facilitate the lithium ion transport process but also stabilize the layered structure against local collapse and structural distortion. This work adopts a dual-site-doping approach to enhance the electrochemical performance and structural stability of Ni-rich cathode materials, which could be extended as a universal modification strategy to improve the electrochemical performance of other cathode materials.