Electrical Transport Research Articles

Doping strategy in metavalently bonded materials for advancing thermoelectric performance

Metavalent bonding is a unique bonding mechanism responsible for exceptional properties of materials used in thermoelectric, phase-change, and optoelectronic devices. For thermoelectrics, the desired performance of metavalently bonded materials can be tuned by doping foreign atoms. Incorporating dopants to form solid solutions or second phases is a crucial route to tailor the charge and phonon transport. Yet, it is difficult to predict if dopants will form a secondary phase or a solid solution, which hinders the tailoring of microstructures and material properties. Here, we propose that the solid solution is more easily formed between metavalently bonded solids, while precipitates prefer to exist in systems mixed by metavalently bonded and other bonding mechanisms. We demonstrate this in a metavalently bonded GeTe compound alloyed with different sulfides. We find that S can dissolve in the GeTe matrix when alloyed with metavalently bonded PbS. In contrast, S-rich second phases are omnipresent via alloying with covalently bonded GeS and SnS. Benefiting from the reduced phonon propagation and the optimized electrical transport properties upon doping PbS in GeTe, a high figure-of-merit ZT of 2.2 at 773 K in (Ge0.84Sb0.06Te0.9)(PbSe)0.05(PbS)0.05 is realized. This strategy can be applied to other metavalently bonded materials to design properties beyond thermoelectrics.

Pressure-induced extreme anisotropic behavior of thermoelectric properties in crystalline β-CuSCN

Applying hydrostatic pressure has emerged as a promising strategy for regulating the properties of thermoelectric materials, particularly in the case of β-CuSCN, which has garnered attention due to its ultra-low thermal conductivity and potential applications in thermoelectric devices. Herein, we investigate the intrinsic mechanism governing the electron-thermal transport properties of β-CuSCN under hydrostatic pressure. It was found that ZT decreased by 30 % along the in-plane direction while increasing by 24 % along the out-of-plane direction following the application of hydrostatic pressure, respectively. Our results reveal that the competitive relationship between pressure-driven effects on phonon dynamics and electronic structure influences the thermoelectric properties of β-CuSCN. For the transport mechanism, the compression alters phonon dispersion by enhancing atomic interactions, which leads to an increase in lattice thermal conductivity. On the other hand, despite strong coupling between electrical transport parameters, a net increase in power factor is achieved through pressure-induced bandgap narrowing. As a result, the thermoelectric properties demonstrate contrary variation tendency along the in-plane and out-of-plane directions. Our research deepens our understanding of transport behavior under extreme pressure conditions and provides valuable insights into the fundamental relationship between structural deformation and thermoelectric performance.

Stabilizing Distorted Ductile Semiconductors for Excellent Ductility and Thermoelectric Performance

AbstractElement doping/alloying is a common strategy to tune the electrical and thermal transports of thermoelectric (TE) materials, but the doping/alloying limit of foreign elements in many TE materials is usually very low, bringing a great challenge to improve the TE performance. In this work, beyond the classic principle of “like dissolves like,” it is found that choosing the compound with a severely distorted lattice and diversified chemical bonding as the matrix also facilitates achieving a high doping/alloying limit. Taking ductile semiconductors as an example, this work shows that gold (Au) element is nearly immiscible in Ag2S and Ag2Te, but has a relatively high alloying limit in complex Ag2S0.5Te0.5 meta‐phase. Au in Ag2S0.5Te0.5 significantly decreases the carrier concentration and improves the TE performance, but scarcely changes the mechanical properties. Consequently, Ag1.99Au0.01S0.5Te0.5 demonstrates both a high figure‐or‐merit of 0.95 at 550 K and extraordinary room‐temperature ductility. This work offers an effective and general strategy to develop stabilized doped/alloyed TE materials.

Bias voltage modulated electric transport properties in Fe65Co35/Hf0.5Zr0.5O2 films

We demonstrate the bias voltage modulated electric transport properties in Fe65Co35 (FeCo) films deposited on Hf0.5Zr0.5O2 (HZO) films. Intrinsic multiferroicity have been characterized for the FeCo/HZO heterostructures by analyzing the ferroelectric polarizations and imaging the magnetic domains. We show that, upon the application of bias voltages on the FeCo/HZO heterostructures, the current-voltage (I-V) curves of FeCo films can be regulated, giving rise to different resistance states, enabled partly by strain-mediated magnetoelectric coupling effect. The strain coupling effect between HZO and FeCo films is elucidated by simulating the volumetric strain of the FeCo/HZO films under the action of applied voltages. Through additional analysis, the bias voltage modulated electric transport properties could also be linked with charge-mediated magnetoelectric coupling effect. We anticipate that our work will inspire further studies on low-power consumption and high-density electronic devices.

Full-shell d-orbitals of interstitial Ni and anomalous electrical transport in Ni-based half-Heusler thermoelectric semiconductors

We systematically investigate the anomalous electronic properties and electrical transport induced by full-shell d10-orbitals of the extra interstitial Nii in Ni-based half-Heusler XNi1+xZ semiconductors. The orbitals from the interstitial Nii have the unique d10 configuration, split into high-energy eg4 orbitals and low-energy t2g6 orbitals under the octahedral crystal field. In XIVNi1+xZIV (XIV=Ti, Zr, Hf; ZIV=Sn, Pb), the localized Nii-eg4 states fall within the intrinsic bandgap leading to a reduced bandgap. In XIIINi1+xZV (XIII=Sc, Y; ZV=Sb, Bi), the Nii-eg4 states overlap with the intrinsic valence bands. Additionally, the interstitial Nii perturb the nearest neighbor X atomic coordination, leading to the splitting of degenerate conduction band minimum, which is stronger in XIIINi1+xZV than XIVNi1+xZIV. Trace amounts of interstitial Nii significantly impact the electrical transport properties. The introduction of the extra interstitial Nii reduces the density of states effective mass, the electron group velocity, and the relaxation time, leading to a decrease of the Seebeck coefficient and electrical conductivity at low and medium temperatures. Nevertheless, the introduction of localized Nii-eg4 states within the bandgap as new valence band maximum attenuate the high-temperature bipolar effect at low carrier concentration intervals, thus maintaining a high thermopower at elevated temperatures. Furthermore, the tuning of the Nii-d10 orbitals by solid solution of both XIVNi1+xZIV and XIIINi1+xZV is expected to further optimize the electrical transport.

Review on techno-socio-economic studies of electric vehicles in electrical energy systems

Transportation electrification is a practical solution for the world's environmental, economic, and technical challenges. During the last decades, numerous studies have focused on electric vehicles (EVs) as one of the essential energy fields due to the growth rate of EV penetration into energy systems. Researchers have investigated different operation and long-term planning models of EV charging infrastructure and prediction and uncertainty-handling approaches for EV drivers’ behavior (i.e., the arrival/departure time to/from charging stations and the associated state-of-charge) as well as fixed and mobile charging stations (MCSs) and social equity access to EV charging infrastructure. This study provides a detailed analysis and discussion of the daily operation and long-term planning of EV charging stations with economic and technical aspects. Also, the prediction of EV drivers’ behavior and approaches to dealing with uncertain EV parameters are studied. Furthermore, the role of MCSs and social equity access in planning EVs’ charging station placement is investigated. The authors also assess the applications of permanent and MCSs and the social equity access to EV infrastructure. Finally, the current study discusses EVs future trends and their effect on electrical systems as future subjects of research studies.

The effect of MgO addition on thermomechanical and electrical transport properties of La0.5Sr0.5FeO3–δ perovskite-like ferrite

Composite materials La0.5Sr0.5FeO3–δ/MgO (LSF/MgO) were synthesized by glycine-nitrate route. Phase composition was checked using X-Ray diffraction (XRD) method. Composite microstructure was confirmed by microscopic methods. MgO addition was found to facilitate sintering of the composites. Thermal expansion studies have shown that LSF/MgO materials tend to possess lower thermal expansion coefficient (TEC) with increasing of MgO addition. Measuring electrical conductivity of the composites has shown the increase of MgO content leads to non-monotonous decrease of samples’ conductance. An effective medium theory (EMT) is utilized to explain the observed feature. The obtained model parameters are used to evaluate hydrogen production rate from 1 cm2 of ceramic membrane’s surface in water splitting coupled to partial oxidation of methane (WS-POM) process. It is suggested that the addition of MgO in the amount of 3–6 mass % to LSF can be a perspective tool for improving WS-POM efficiency.

The Catalytic Effect of Low Molecular Weight Acids on the Physicochemical and Dielectric Properties of Oil-Paper Insulation Systems.

In most industrialized countries, power transformers built several decades ago are approaching the end of their operational lifespan. The ongoing energy transition, focused on developing 100% renewable energy sources and accelerating global transportation electrification, further exacerbates these assets. Combined with rising electricity demand, there is an increasing risk of critical transformers' degradation acceleration. In this context, understanding the aging mechanisms of the insulation system inside these essential assets, which form the core of every energy network, becomes paramount for today's managers and engineers responsible for their operations. The acids generated through oil oxidation can be classified into two categories: low molecular weight acids (LMAs), which are inherently more hydrophilic and consequently have a greater impact on the degradation rate of solid insulation through hydrolysis, and high molecular weight acids (HMAs), which do not significantly contribute to the degradation of paper insulation. This study specifically addresses the impact of acids generated through oil oxidation-focusing on LMAs. New oil samples were infused with different ratios of LMAs before impregnation. The impregnated paper samples underwent thermal aging at 115 °C. Different physicochemical and dielectric properties were investigated. The investigations revealed that oils blended with formic acid exhibited more adverse effects on the insulation system compared to other LMAs. This information is essential for industry professionals seeking to mitigate the risks associated with transformer degradation and extend the lifespan of these critical assets during the energy transition.

Analyzing Energy Efficiency and Battery Supervision in Electric Bus Integration for Improved Urban Transport Sustainability

Addressing the critical challenge of reducing local emissions through the electrification of urban public transport, this research specifically focuses on integrating electric buses. The primary objectives are to evaluate energy efficiency and ensure battery cell supervision. Introducing electric buses plays a significant role in reducing emissions, contributing to more sustainable urban transport systems. However, this transition introduces a set of new challenges, including the complexities of electric charging logistics, the establishment of new consumption standards, and the intricate relationships between distance traveled, ambient temperature, passenger load, and battery health. Methodologically, this study collects and examines factors impacting energy consumption, including external temperatures, bus conditions, road conditions, and driver behavior. By analyzing these variables, a baseline for actual consumption can be established, allowing for the calculation of an energy balance to identify energy inefficiencies. This enables the optimization of route planning, the strategic selection of stops, and the efficient scheduling of charging times, along with ensuring the proper scaling of the bus battery system. This study found that energy consumption peaked at 116.73 kWh/100 km in the lowest temperature range of −5 °C to 0 °C. Consumption decreased significantly with rising temperatures, dropping by 25 kWh between 5 °C and 10 °C and by an additional 10 kWh between 10 °C and 15 °C. Beyond 20 °C, variations were more influenced by route and driving style than by temperature. Route and driver variability significantly influenced energy consumption, with up to threefold differences across routes due to factors such as road type and traffic volume. Additionally, there was a 31.85% difference between the most and least efficient drivers, highlighting the critical impact of driving style. Furthermore, this study explores the assessment of battery systems through cell-level diagnostics to detect potential faults. Considering that buses are equipped with significantly more batteries than typical electric vehicles, detecting and localizing faults at the cell level is crucial to avoid the substantial costs and environmental impact associated with replacing large battery systems. Utilizing the results of this research and the applied examination methods, it is possible to enhance energy efficiency and extend battery life, thereby contributing to the development of more sustainable and cost-effective urban transport solutions.

The Liquid Metal Age: A Transition From Hg to Ga.

This review offers an illuminating journey through the historical evolution and modern-day applications of liquid metals, presenting a comprehensive view of their significance in diverse fields. Tracing the trajectory from mercury applications to contemporary innovations, the paper explores their pivotal role in industry and research. The analysis spans electrical switches, mechanical applications, electrodes, chemical synthesis, energy storage, thermal transport, electronics, and biomedicine. Each section examines the intricacies of liquid metal integration, elucidating their contributions to technological advancements and societal progress. Moreover, the review critically appraises the challenges and prospects inherent in liquid metal applications, addressing issues of recycling, corrosion management, device stability, economic feasibility, translational hurdles, and market dynamics. By delving into these complexities, the paper advances scholarly understanding and offers actionable insights for researchers, engineers, and policymakers. It aims to catalyze innovation, foster interdisciplinary collaboration, and promote liquid metal-enabled solutions for societal needs. Through its comprehensive analysis and forward-looking perspective, this review serves as a guide for navigating the landscape of liquid metal applications, bridging historical legacies with contemporary challenges, and highlighting the transformative potential of liquid metals in shaping future technologies.

Effects of ZnO additive on the electrical and densification properties of A-site deficient barium cerate perovskite

The dual strategies of A-site deficiency and addition of ZnO sintering aid have been employed to optimise stability and densify the high-temperature proton conductor Ba0.95Ce0.8Y0.2O3-δ at 1200 °C (B95CYZn-1200). Structural analysis performed by Rietveld refinement based on X-ray diffraction data indicated perovskite phase with monoclinic symmetry (space group, I2/m). Raman spectroscopy revealed the presence of ZnO for material sintered at 1200 °C, which most likely partially resides in grain-boundary regions, leading to enhanced electrical transport observed by impedance spectroscopy at low temperature. Anomalous and reproducible frequency-dependent impedance behaviour below 500 °C, observed in various atmospheres, is suggested to be attributable to the varistor-type properties of ZnO. The electrical conductivity of B95CYZn-1200 in the range 500–900 °C is typical of perovskite proton conductors but with greater conductivity than both Ba-stoichiometric BaCe0.8Y0.2O3-δ and ZnO-free Ba0.95Ce0.8Y0.2O3-δ in wet O2 and N2, reaching ∼ 1.1 S m−1 at 550 °C in wet O2. Resistance to carbonate formation and mechanical breakdown was demonstrated via prolonged impedance measurements in CO2- and H2-containing atmospheres in the range 600–700 °C.

Synthesis, Crystal and Electronic Structures, and Magnetic and Electrical Transport Properties of Bismuthides NdZn0.6Bi2 and (La0.5RE0.5)Zn0.6Bi2 (RE = Pr or Nd).

Bismuth is a good constituent element for many quantum materials due to its large atomic number, 6s26p3 orbitals, and strong spin-orbital coupling. In this work, three new bismuthides, NdZn0.6Bi2, (La0.5Pr0.5)Zn0.6Bi2, and (La0.5Nd0.5)Zn0.6Bi2, were grown by a metal flux method, and their crystal structures were accurately determined by single-crystal X-ray diffraction. These new bismuthides belong to the RE-T-Pn2 (RE = La-Lu, T = Mn, Fe, Co, Ni, or Zn, and Pn = P, As, Sb, or Bi) family, are isostructural, and crystallize in the HfCuSi2 structure type. The bismuth elements have two possible oxidation states, Bi3- and Bi-, which were studied by X-ray photoelectron spectroscopy (XPS). Two binding energy peaks of 155.91 and 161.23 eV were observed for Bi atoms within NdZn0.6Bi2, and similar binding energy peaks were detected in NdBi and LiBi. XPS also confirmed the trivalent nature of Nd, which was further verified by magnetic measurements. Additionally, magnetic measurements revealed that NdZn0.6Bi2 exhibits an antiferromagnetic transition around 3 K, while the mixed-cation compounds do not show any magnetic transition down to 2 K. Electronic transport measurements reveal weak magnetoresistance in all three compounds, with a maximum value of ∼25% at 2 K and 9 T for (La0.5Nd0.5)Zn0.6Bi2.

Optimizing dose parameters for enhanced maskless lithography in MoS2-based devices

Maskless lithography simplifies the fabrication process and reduces costs compared to electron beam (E-beam) lithography, making it a more efficient choice for patterning nano-devices. Maskless lithography presents a promising avenue for expediting device fabrication by eliminating the need for masks. This technique can streamline the production of basic electronic devices, offering an efficient and low-cost alternative to traditional lithographic methods, like E-beam lithography. This study utilized a 405 nm photodiode to achieve pattern-writing with a minimum linewidth of 1 μm. Exploring optimal parameters includes adjustments in beam intensity, scan speed, and step size. Maskless lithography was applied to 2D transition metal dichalcogenides (TMDCs) material, MoS2, to investigate their electrical transport characteristics. The fabricated device exhibits an ON/OFF ratio of ∼1.7 × 106 and a mobility of ∼0.833 cm2/V·s, indicating a high switching efficiency. The results demonstrate optimized maskless lithography's potential for swift and cost-effective fabrication, offering intermediate-resolution patterning capabilities.

Understanding disorder in monolayer graphene devices with gate-defined superlattices

Engineering superlattices (SLs)-which are spatially periodic potential landscapes for electrons-is an emerging approach for the realization of exotic properties, including superconductivity and correlated insulators, in two-dimensional materials. While moiré SL engineering has been a popular approach, nanopatterning is an attractive alternative offering control over the pattern and wavelength of the SL. However, the disorder arising in the system due to imperfect nanopatterning is seldom studied. Here, by creating a square lattice of nanoholes in the SiO2dielectric layer using nanolithography, we study the SL potential and the disorder formed in hBN-graphene-hBN heterostructures. Specifically, we observe that while electrical transport shows distinct SL satellite peaks, the disorder of the device is significantly higher than graphene devices without any SL. We use finite-element simulations combined with a resistor network model to calculate the effects of this disorder on the transport properties of graphene. We consider three types of disorder: nanohole size variations, adjacent nanohole mergers, and nanohole vacancies. Comparing our experimental results with the model, we find that the disorder primarily originates from nanohole size variations rather than nanohole mergers in square SLs. We further confirm the validity of our model by comparing the results with quantum transport simulations. Our findings highlight the applicability of our simple framework to predict and engineer disorder in patterned SLs, specifically correlating variations in the resultant SL patterns to the observed disorder. Our combined experimental and theoretical results could serve as a valuable guide for optimizing nanofabrication processes to engineer disorder in nanopatterned SLs.

Investigation of cabin heating in electric vehicles with integrating solar cells and heat storage systems

In recent years, the production and usage of electric vehicles have been encouraged due to zero emissions, efficiency, and economic factors. Efficient cabin heating and thermal management in electric vehicles are crucial for enhancing passenger comfort, extending battery life, and optimizing overall energy usage, thus contributing to the sustainability and practicality of electric transportation. Heating the cabin of electric vehicles in winter has a negative effect on range. Therefore, methods are being researched to use energy efficiently without sacrificing passenger comfort and minimizing the effect on the vehicle's range. This study presents an innovative radiator design specifically crafted for Electric Vehicles (EVs), leveraging solar panels to heat water for the radiator. This system enables the vehicle to harness solar energy for heating a water tank while stationary, effectively serving as an energy storage reservoir. Upon vehicle movement, the radiator system activates to disperse the stored thermal energy throughout the cabin, ensuring superior thermal comfort. Consequently, optimizing battery range is achieved as the heating load typically leads to significant range reductions. From the obtained results in experiment 2, the results indicated that the cabin temperature rose from 3 °C to around 15 °C within a few minutes, reflecting an increase of approximately 12 °C. According to the results, this indicates that there will be a reduction in energy consumption of between 1.9 % and 3 % for a one-hour travel range in this electric vehicle. The findings of this investigation demonstrate that utilizing warm water energy storage effectively enhances cabin thermal management.

Optimization of Co4Sb11.5Te0.5 thermoelectric performance through Al filling under high temperature and high pressure

So far, the method of optimizing the thermoelectric properties of skutterudite CoSb3 is usually to achieve a breakthrough in high-properties thermoelectric merit by selecting excellent doping atoms and determining a reasonable percentage of atoms. In this study, we achieved the preparation of small atomic radius Al-filled Co4Sb11.5Te0.5 compounds by high-temperature and high-pressure (HTHP) synthesis methods. The thermoelectric properties of the samples AlxCo4Sb11.5Te0.5 were optimized from two dimensions: synthesis pressures (1.0 GPa, 1.5 GPa, 2.0 GPa) and Al filling concentration (x = 0.1, 0.2, 0.3, 0.5), ultimately achieving effective decoupling of electron-phonon transport properties. The experimental results show that Al doping can optimize the electrical transport properties of materials effectively, rapid synthesis method of HTHP can introduce abundant grain boundaries, diversification of grain sizes, a large number of dislocations and widely distributed nano second phase, etc. These microstructures in bulk materials form a multi-scale phonon scattering network in situ, which can effectively scatter phonons and reduce the lattice thermal conductivity effectively. After optimizing the synthesis pressure and Al filling concentration through orthogonal transformation, the sample Al0.3Co4Sb11.5Te0.5 prepared at a synthesis pressure of 1.5 GPa obtained a minimum lattice thermal conductivity value of 0.88 W m−1 K−1, a maximum power factor of 40.96 μ W cm−1 K−2 and a maximum zT value of 1.18 at 773.15 K.

Effect of insulator matrix on electrical transport properties of iron-insulator discontinuous multilayers

This work presents the results of the study of structural and electrical transport properties of the iron-insulator discontinuous multilayers (DMIMs). SiO2, HfO2, and MgO were chosen as the materials for the insulating layers. The discontinuous multilayers were prepared by the sequential magnetron sputtering on ceramic substrates. Obtained systems were annealed at different temperatures in an Ar + N2(2 %) environment using an annealing furnace with a continuous gas flow. Crystal structure analysis showed that the effect of annealing on the crystal structure of the samples varies and depends on the annealing temperature and the type of insulator. It has been demonstrated that the formation of iron oxide during annealing can be reduced by using HfO2 as the insulating layer material. The resistivity and temperature coefficient of resistance variation with temperature and the effective thicknesses of the ferromagnetic layers were analyzed.

The thermoelectric properties of the two-dimensional Nowotny-Juza material NaBeX (X = P, As, and Sb)

The two-dimensional β-type Nowotny-Juza phase-filled tetrahedral compound has excellent electrical conductivity, low thermal conductivity and outstanding thermoelectric properties. This study investigated the stability and electronic properties of NaBeX (X = P, As, and Sb) through first-principles calculations. The results demonstrate that these materials are structurally stable and are direct bandgap semiconductors with bandgaps of 0.6542 eV, 0.6549 eV, and 0.6686 eV, respectively. The electrical and thermal transport properties of NaBeX are investigated by combining the deformation potential theory and Boltzmann transport theory. Subsequently, the thermoelectric properties of NaBeX are evaluated at temperatures ranging from 400 to 800 K. The n-type NaBeX materials exhibit large ZT values of 2.48, 2.62, and 1.72. The results of the present study indicate that n-type NaBeX has the potential to be used as a thermoelectric candidate material at temperatures ranging from 400 to 800 K.

Gate induced metallicity and absence of superconductivity in BSTO/LCO heterostructure

We fabricated Ba0.8Sr0.2TiO3 (BSTO)/La2CuO4 (LCO) heterostructure on SrTiO3 (STO) substrate and investigated its structure and physical properties. X-ray diffraction and reciprocal space mapping confirm the epitaxial growth of BSTO/LCO/STO heterostructure. X-ray photoelectron spectroscopy and UV–Visible spectroscopy measurements reveal a straddling band alignment of the BSTO/LCO heterojunction. Such band alignment facilitates the accumulation of both electrons and holes at the interface. Their movement depends on the direction of the internal field of the BSTO film. Electrical transport measurements have revealed a signature of insulator-to-metal transition (IMT) in response to applied gate voltages ±Vg. Hall measurements confirm the presence of electron and hole type charge carriers under ＋Vg and −Vg, respectively. We have proposed a screening mechanism linked to the polarization state of the BSTO film to explain the observed IMT.

Evolving Synergy Between Synthetic and Biotic Elements in Conjugated Polyelectrolyte/Bacteria Composite Improves Charge Transport and Mechanical Properties.

gLiving materials can achieve unprecedented function by combining synthetic materials with the wide range of cellular functions. Of interest are situations where the critical properties of individual abiotic and biotic elements improve via their combination. For example, integrating electroactive bacteria into conjugated polyelectrolyte (CPE) hydrogels increases biocurrent production. One observes more efficient electrical charge transport within the CPE matrix in the presence of Shewanella oneidensis MR-1 and more current per cell is extracted, compared to traditional biofilms. Here, the origin of these synergistic effects are examined. Transcriptomics reveals that genes in S. oneidensis MR-1 related to bacteriophages and energy metabolism are upregulated in the composite material. Fluorescent staining and rheological measurements before and after enzymatic treatment identified the importance of extracellular biomaterials in increasing matrix cohesion. The synergy between CPE and S. oneidensis MR-1 thus arises from initially unanticipated changes in matrix composition and bacteria adaption within the synthetic environment.