Room-temperature Applications Research Articles

Magnetocaloric properties of melt-spun MnFe-rich high-entropy alloy

High-entropy functional materials are of great interest in materials science and engineering community. In this work, ab initio electronic structure calculations of the phase stability and magnetic transition temperature of AlxCr0.25MnFeCo0.25−yNiy (x = 0–0.5, y = 0–0.25) alloys were performed to screen for compositions showing promising magnetocaloric properties in the vicinity of room temperature. The selected Al0.44Cr0.25MnFeCo0.05Ni0.2 alloy was synthesized via a rapid solidification technique and systematically characterized with respect to its structural and magnetocaloric properties. The results indicate that this alloy possesses a homogeneous microstructure based on an underlying body-centered cubic lattice and has a Curie temperature of ∼340 K. The temperature dependence of the adiabatic temperature change was evaluated using both direct and indirect methods. The ab initio-assisted design of 3d-metal-based high-entropy alloys, explored here, is intended to contribute to the development of magnetic refrigerators for room-temperature applications.

Large gap two-dimensional topological insulators with prominent Rashba effect in ethynyl functionalized Ⅲ-Bi Buckled-Honeycomb monolayers

Recently, two-dimensional topological insulators have attracted extensive attention because of their excellent electronic transport performance and easy integration into electronic devices. However, the small bandgap limits their room-temperature application. Based on first-principles calculations, we predict that the ethynyl functionalized GaBi/InBi monolayers are topological insulators with large bandgap ( E g = 0.512 e V ) and significant Rashba SOC effect ( α R = 2.819 eVÅ ). The topological phases, which originate from s-p x,y band inversion induced by chemical bonding, can be maintained within the large-range biaxial strain. Additionally, the h -BN is found to be an ideal substrate for the growth of these QSH insulators. These findings indicate that the ethynyl functionalized Ⅲ-Bi monolayers are expected to be candidate materials for spintronics and quantum computing . These findings indicate that the ethynyl functionalized Ⅲ-Bi monolayers are expected to be candidate materials for spintronics and quantum computing. • We predict that the ethynyl functionalized GaBi/InBi monolayers are topological insulators with large bandgap ( E g = 0.512 eV ) and significant Rashba SOC effect ( α R = 2.819 eVÅ ) . • We research the strain engineering and explain the change in topology phase through evolution of orbitals. • We study the significant Rashba SOC effect and the electric field impact. • The h -BN is found to be an ideal substrate for the growth of these QSH insulators.

Barocaloric properties of quaternary Mn3(Zn,In)N for room-temperature refrigeration applications

The magnetically frustrated manganese nitride antiperovskite family displays significant changes of entropy under hydrostatic pressure that can be useful for the emerging field of barocaloric cooling. Here we show that barocaloric properties of metallic antiperovskite Mn nitrides can be tailored for room-temperature application through quaternary alloying. We find an enhanced entropy change of $|\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{t}}|=37\phantom{\rule{4pt}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}$ at the ${T}_{t}=300\phantom{\rule{4pt}{0ex}}\mathrm{K}$ antiferromagnetic transition of quaternary ${\mathrm{Mn}}_{3}{\mathrm{Zn}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{N}$ relative to the ternary end members. The pressure-driven barocaloric entropy change of ${\mathrm{Mn}}_{3}{\mathrm{Zn}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{N}$ reaches $|\mathrm{\ensuremath{\Delta}}{S}_{\mathrm{BCE}}|=20\phantom{\rule{4pt}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}$ in 2.9 kbar. Our results open up a large phase space where compounds with improved barocaloric properties may be found.

Unraveling peculiar magnetism and band topology in Mn3Sb

Magnetic, pseudogap, topological, magnetostructural, and elastic behaviors of Mn3Sb have been unraveled. The ferrimagnetism (FIM) is described by localized and delocalized electron magnetism resulting in different magnetic moments on Mn atoms, confirming the neutron diffraction data. The identified magnetostructural properties are due to the non-equivalent Mn atoms in its lowest symmetry structure. The electronic structure is also unique due to variable valance states of Mn atoms. The magnetic moment (4.10 μB) of non-equivalent Mn1 atom is antiparallely aligned with the magnetic moments (2.34 μB) of Mn2 and Mn3 atoms. The estimated Curie temperature, TC, is higher than the room temperature, which may have above the room temperature applications in spintronic devices. The band structure and density of states (DOS) show the characteristics of band topology (opening of a gap in Dirac-like band features) and pseudo-gap, respectively, around the Fermi level. While expanding the unit cell, the tetragonal FIM ground state transforms to the cubic primitive FIM phase, however, the contraction transforms it to the L12 ferromagnetic (FM) phase. The estimated elastic constants, bulk to shear modulus ratio, and elastic anisotropy factor indicate that Mn3Sb exhibits mechanically stable, ductile, and anisotropic behaviors, respectively.

Design and realization of topological Dirac fermions on a triangular lattice

Large-gap quantum spin Hall insulators are promising materials for room-temperature applications based on Dirac fermions. Key to engineer the topologically non-trivial band ordering and sizable band gaps is strong spin-orbit interaction. Following Kane and Mele’s original suggestion, one approach is to synthesize monolayers of heavy atoms with honeycomb coordination accommodated on templates with hexagonal symmetry. Yet, in the majority of cases, this recipe leads to triangular lattices, typically hosting metals or trivial insulators. Here, we conceive and realize “indenene”, a triangular monolayer of indium on SiC exhibiting non-trivial valley physics driven by local spin-orbit coupling, which prevails over inversion-symmetry breaking terms. By means of tunneling microscopy of the 2D bulk we identify the quantum spin Hall phase of this triangular lattice and unveil how a hidden honeycomb connectivity emerges from interference patterns in Bloch px ± ipy-derived wave functions.

Field-controlled tunability of novel multifunctional phenomena in Tb-substituted La2CoMnO6: Role of antisite disorder

Multifunctional materials have gained huge attention owing to their great possibility in device applications. However, producing single-phase multifunctional materials, associated with various novel properties, has been proved to be a serious challenge. A simple yet effective way to overcome this barrier, is therefore of great importance. Here, we report the evolution of temperature- and magnetic field-dependent novel multifunctional phenomena in polycrystalline La2-xTbxCoMnO6. Substitution of Tb in ferromagnetic La2CoMnO6, induces antiferromagnetic ordering through development of antisite disorder and antiphase boundaries, and results in a phase separation between ferromagnetic/antiferromagnetic layers. This originates the coexistence of conventional and inverse magnetocaloric effects in this system. The switching between them, with its tunability with temperature and magnetic field, suggests a huge potential of this compound. In addition, a clear correlation is established between the magnetocaloric switching and field-induced metamagnetic transitions. Furthermore, the discovery of tunable giant exchange bias (~1.8 kOe) at very low cooling field (500 Oe), a reasonable self-exchange bias (270 Oe), and a large negative magnetoresistance (~14%), makes this system enormously attractive for practical applications and fundamental research. The present study proposes a novel and effective route for successfully preparing essential multifunctional compounds to open a new pathway toward room-temperature applications.

Switching Behavior of a Heterostructure Based on Periodically Doped Graphene Nanoribbon

We theoretically propose a switching device that operates at room temperature. The device is an in-plane heterostructure based on a periodically boron-doped (nitrogen-doped) armchair graphene nanoribbon, which has been experimentally fabricated recently. The calculated $I$-$V$ curve shows that for a realistic device with interface width longer than $20$ nm, nonzero electric current occurs only in the region of bias voltage between $\ensuremath{-}0.22$ and $0.28$ V, which is beneficial to low-voltage operation. Furthermore, in this case, the electric current is robust against the change of the potential profile in the interface since the metallic impurity-induced sub-bands with delocalized wave functions contribute to the transmission exclusively. This also suggests the high response speed of the proposed device. We also discuss the temperature dependence, the output impedance, the effect of phonons, and the possible regimes to extend our work, which suggest that our model may have potential room-temperature nanoelectronics applications.

Cr2NX2 MXene (X = O, F, OH): A 2D ferromagnetic half-metal

Using the spin-polarized first-principles calculations, we revealed that two-dimensional transition metal nitride MXenes Cr2NX2 (X = O, F, OH) are excellent two-dimensional half-metallic ferromagnetic materials. Their structures and ferromagnetic ground states are stable well above room temperature. In addition, their large half-metal bandgaps are enough to prevent spin reversal and ensure high spin filtering efficiency and large spin mean free paths. The half-metallic property of these functionalized Cr2NX2 systems is robust and can be maintained under tensile strains up to 10%. These predictions suggest that the functionalized Cr2NX2 is of great significance for the development of highly efficient spintronic devices for room temperature applications.

Thermoelectric properties of the SnS monolayer: Fully ab initio and accelerated calculations

An energetic and dynamical stability analysis of five candidate structures—hexagonal, buckled hexagonal, litharge, inverted litharge, and distorted-NaCl—of the SnS monolayer is performed using density functional theory. The most stable is found to be a highly distorted-NaCl-type structure. The thermoelectric properties of this monolayer are then calculated using the density functional theory and the Boltzmann transport equation. In terms of phonon scattering, there is a sharp contrast between this monolayer and bulk materials, where normal processes are more important. The calculations reveal that the SnS monolayer has enhanced electrical performance as compared to the bulk phase. As a consequence, high figures of merit ZT∼5 and ZT∼1.36 are predicted at 600 and 300 K, respectively, for the monolayer, ∼33 times higher than the ZT of its bulk analog. Therefore, this structure is an interesting candidate for room-temperature thermoelectric applications. A comparison between the fully ab initio results and simpler models based on relaxation times for electrons and phonons highlights the efficiency of computationally inexpensive models. However, ab initio calculations are found to be very important for the prediction of thermal transport properties.

Origin and enhancement of the spin Hall angle in the Weyl semimetals LaAlSi and LaAlGe

We study the origin of the strong spin Hall effect (SHE) in a recently discovered family of Weyl semimetals, LaAl$X$ ($X$=Si, Ge) via a first-principles approach with maximally localized Wannier functions. We show that the strong intrinsic SHE in LaAl$X$ originates from the multiple slight anticrossings of nodal lines and points near $E_F$ due to their high mirror symmetry and large spin-orbit interaction. It is further found that both electrical and thermal means can enhance the spin Hall conductivity ($\sigma_{SH}$). However, the former also increases the electrical conductivity ($\sigma_{c}$), while the latter decreases it. As a result, the independent tuning of $\sigma_{SH}$ and $\sigma_{c}$ by thermal means can enhance the spin Hall angle (proportional to $\frac{\sigma_{SH}}{\sigma_{c}}$), a figure of merit of charge-to-spin current interconversion of spin-orbit torque devices. The underlying physics of such independent changes of the spin Hall and electrical conductivity by thermal means is revealed through the band-resolved and $k$-resolved spin Berry curvature. Our finding offers a new way in the search of high SHA materials for room-temperature spin-orbitronics applications.

Cu nanoparticle-processed n-type Bi2Te2.7Se0.3 alloys for low-temperature thermoelectric power generation

Bi-Te-based materials have been used for room-temperature thermoelectric applications. However, n-type Bi2(Te,Se)3 thermoelectric alloys show a limited conversion efficiency, as compared to their p-type counterparts, thus hindering further widespread room-temperature applications. In this study, we investigated the enhanced thermoelectric properties of n-type Bi2(Te,Se)3 materials by the addition of Cu nanoparticles via a conventional high-energy ball milling process. The electrical and thermal transport properties were modulated by changing the amount of Cu nanoparticles. The power factor was enhanced by controlling the carrier, and the total thermal conductivity was reduced mainly due to the reduction in electronic thermal conductivity. Thus, dimensionless thermoelectric figure of merit (zT) at room temperature was enhanced for the Cu-added samples, and the highest zT value of 0.85 at 375 K was achieved in 2% Cu-doped Bi2Te2.7Se0.3. The average zT (zTavg) value between room temperature and 500 K was 0.79 for the 2% Cu-doped Bi2Te2.7Se0.3, which was 20% higher than that of the pristine Bi2Te2.7Se0.3, whereas a zT higher than 0.80 was sustained from room temperature to ~450 K. These results can lead to a high thermoelectric power generation efficiency of 7.6% at ΔT = 200 K.

Room temperature cavity electromechanics in the sideband-resolved regime

We demonstrate a sideband-resolved cavity electromechanical system operating at room temperature. It consists of a nanomechanical resonator, a strongly pre-stressed silicon nitride string, dielectrically coupled to a three-dimensional microwave cavity made of copper. The electromechanical coupling is characterized by two measurements, the cavity-induced eigenfrequency shift of the mechanical resonator and the optomechanically induced transparency. While the former is dominated by dielectric effects, the latter reveals a clear signature of the dynamical backaction of the cavity field on the resonator. This unlocks the field of cavity electromechanics for room temperature applications.

Atomic origin of room-temperature two-dimensional itinerant ferromagnetism in an oxide-monolayer heterostructure

Materials with room-temperature two-dimensional itinerant ferromagnetism enable ultracompact device density and quantum computing in next-generation nano-spintronics. Among numerous candidates, perovskite-based heterostructures have offered an excellent platform to manipulate spin-orbital-charge coupling, unveiling a series of emergent spin-dependent phenomena. In this work, we have fulfilled a robust room-temperature soft ferromagnetism together with a metallic characteristic based on a high quality SrRuO3-monolayer-based superlattice. Further examination on this short-range ferromagnetism has been carried out by synchrotron-related spectroscopy, where charge-transfer-induced antiferromagnetic coupling between partial Ru and Ti ions have been found. Although such local antiferromagnetic coupling would break long range ferromagnetic order, it simultaneously stabilize the localized intralayer ferromagnetic order in the SrRuO3 monolayers, which is confirmed by theoretical calculations. Our study not only represents a methodological advance of achieving fantastic magnetic properties in functional oxide monolayer, but is promising to unlock new opportunities for oxide-based spintronic devices toward room-temperature applications.

Direct View on Non‐Equilibrium Heterogeneous Dynamics in Glassy Nanorods

AbstractAmorphous solids are potential candidates for room temperature applications, such as structural materials, due to their outstanding mechanical properties. For the first time, the local atomic dynamics of amorphous metallic nanorods are spatially resolved at room temperature using electron microscopy. Methodologically, quasi‐equilibrium conditions are verified by two‐time correlation functions. FeNiP is chosen as a suitable model system since a bamboo structure forms upon electrodeposition into nanotubular confinement, consisting of thin Fe‐rich and Ni‐rich amorphous layers. Therefore, the present nano‐glassy structure allows studying the glass dynamics of two glassy phases at once, at the same time avoiding any preparation‐related structural artifacts of the intrinsically electron‐transparent samples. By comparing the local atomic mobility with the local composition and the local structural information of the glassy phases, correlations between medium‐range order and time scales of heterogeneous glassy dynamics are consistently obtained.

Design and Optimization of Thermoelectric Devices Toward Geometric Aspects and a Promising Electrode for Room-Temperature Wearable Applications

This paper presents a novel wearable thermoelectric device (WTED) to harvest energy from human body heat and convert it into electricity for low-power electronics or sensors applications. To achieve a high-performance WTED, numerical predictions and optimizations for leg geometry, electrode design, and solder paste are essential parameters. Here, Bi2Te3 is used as p- and n-type thermoelectric (TE) materials, Cu electrode, and Sn63Pb37 are used as a solder layer. First, we identify the best geometric shapes (Cylindrical, Cone, or Rectangular) along with varying TE leg length and area through numerical simulations. Among these, the rectangular shape produces better WTED performance. On the other hand, introducing a Ni metalized layer in a rectangular shape with Ni intermediate layer gives an enhanced performance. Then, the best WTED numerical simulation parameters of rectangular shapes with optimum size and nickel-copper fabric electrodes are considered for the novel wearable device fabrication. Finally, a novel four-pair of TE legs for the WTED practical result can generate an output voltage of 0.9 mV with a human body and a room temperature difference of 1 K.

Enhancement of thermoelectric performance of ZrO2 via Titanium doping

In this paper, we investigated the thermoelectric (TE) properties of doped Ti-doped Zirconium Oxide (ZrO2) via first principal calulations together with the Boltzmann transport theory. We computed various TE properties of Zr1−xTixO2 for x = 0.03 and 0.06 within the temperature range of 10 K to 1200 K. This material shows the p- type behaviour in prestine and doped configurations. We achieved Figure of Merit (ZT) arround 0.82 for 3% doping of Ti at 290 K, and this is higher than that of various ZrO2 composites and several oxides like SnO2 and TiO2. Even though Zirconia has low thermal conductivity as compared to other oxides, it is not considered a good TE candidate. Despite this fact we achieved surprisingly good ZT maxima of 0.819 for 3% Ti-doping at 290 K which is 34.22% more than that of the pure material at the same temperature which makes it a good choice for room temperature applications. Hence, we believe that Ti-doped ZrO2, along with its low thermal conductivity, has a great potential to be an efficient TE material.

A Study of thermoelectric properties of Hf-doped RhTiP Half-Heusler alloy

In this work, we present a first-principles based investigation to analyse the effect of Hafnium (Hf) doping on thermoelectric properties of half-Heusler alloy RhTiP. In recent times, Hf based Heuser alloys are proved to be good thermoelectric (TE) materials. So, its interesting to see the effect of Hf, as dopant, on the newly propsed RhTiP. The energy bandgap of pure RhTiP is 0.810 eV. As we start doping, the bandgap first decrease for RhTi0.75Hf0.25P and then increase liearly for higher doping concentrations. We find that the material shows the high thermoelectric performance at 100% doping of Hf in place of Ti (RhHfP) at room temperature. The maximum value of power factor and electrical conductivity at room temperature are estimated, respectively, as 0.19688x1012WK-2m-1s-1 and 3.2058x1018Ω-1m-1s-1 which belong to RhHfP . The maximum ZT value at room temperature is found to be 0.7950 at room and it is too for RhHfP. We estimate that RhHfP can become a good thermoelectric material amongst all the studied concentrations for room temperature applications.

Structure distortion related magnetic anisotropy in 5d transition-metal dimer adsorbed g-C3N4 monolayers

Abstract Among the various two-dimensional (2D) materials, g-C3N4 monolayer has a novel two-dimensional sheet structure with unique characteristics and wide applications. The pristine g-C3N4 is semiconductor with an indirect-band-gap of 1.21 eV. The g-C3N4 adsorbed other materials has proven to be an effective method to change the performance of g-C3N4. Here, we investigated the adsorption energy, stable geometry, electronic structure and magnetic properties of Os, Ir atoms and its dimers adsorbed 2D g-C3N4 monolayers by first-principles calculations. We have considered several possible adsorption sites and select the center of vacancy site after the structure optimization to carry out the further calculations. The Os atom and Os–Ir dimer adsorbed g-C3N4 monolayers are n-type semiconductors, and the Ir–Os, Os–Os and Ir–Ir dimer adsorbed g-C3N4 monolayers are half-metallic. The larger magnetic anisotropy energy (MAE) in the perpendicular direction is more suitable for application than the MAE in the horizontal plane. The MAE of Os adsorbed g-C 3N4 monolayer shows a large perpendicular MAE of 5.192 mJ/m 2 at the tensile strain of 4%. The Ir–Ir adsorbed g-C 3N4 monolayer has the in-plane MAE at compressive strain of −4% and turn into perpendicular MAE of 0.275, 1.516 and 0.361 mJ/m2 at a strain of −6%, 0% and 4%, the Os and Ir–Ir dimer adsorbed g-C3N4 monolayer is promising candidates for room temperature applications. Our results reveal that 5d TM atoms and its dimers adsorbed g-C3N4 monolayers have potential applications in spintronic devices.

Enabling high-energy flexible solid-state lithium ion batteries at room temperature

Flexible solid-state batteries (FSSBs) are indispensable energy storage devices to fulfil the energy and safety requirements for future flexible applications. The bottlenecks of FSSBs are how to realize high energy density with competent ionic conductivity for room-temperature (RT) flexible applications. Here, the first fabrication of RT FSSB with high energy density is reported, which is realized by in situ integration of a 20-µm-thick hybrid polymer/ceramic/ionic liquid solid-state electrolyte (SSE) between the high energy combination of anode/cathode electrodes. The in situ electrode/electrolyte interfacial integration strategy provides an ultrathin SSE layer, ultralow resistance and superior flexibility, and the SSE guarantees both high ionic conductivity and good compatibility with high-energy cathode LiNi0.8Co0.1Mn0.1O2 (NCM811). The fabricated Li4Ti5O12/NCM811 FSSB delivers super-low resistance approaching conventional liquid cells and excellent cycling stability up to 600 cycles at RT. The extension of anode to SiOx@graphite leads to a high theoretical energy density of 489.6 Wh kg−1 at material’s level, times higher than current options. In addition, the RT FSSB shows great flexibility, indicating a high performance application in future flexible electronics.

Microstructure and transition behavior of Fe<sub>2</sub>P-based first-order magnetic phase-transition alloys

<p indent="0mm">Fe₂P-based first-order magnetic phase-transition alloys have been considered as one of the best candidates for room-temperature magnetic refrigeration applications due to their low cost, tunable working temperature range and superior magnetocaloric performance. Previous studies mainly focused on optimizing the magnetocaloric properties as well as uncovering the spin-lattice-electronic multi-coupling in the Fe₂P-based alloys, while the structure and phase transition behavior at the micrometer scale have rarely been reported. In the present study, we performed intensive studies on the microstructure and phase transition behavior in the Fe₂P-based alloys by means of transmission electron microscopy and X-ray powder diffraction (XRD). SiO₂ and Fe₃Si-type secondary phases with micrometer or sub-micrometer sizes are distributed along the grain boundary. <italic>In-situ</italic> XRD measurements indicate that the paramagnetic-ferromagnetic (PM-FM) transition is accompanied with significant lattice distortion in the hexagonal structure. The hexagonal unit cell is expanded by approximately 0.8% along the <italic>a</italic> axis, while it is contracted by about 1.8% along the <italic>c</italic> axis. The serve lattice distortion will induce large elastic energy, raise the energy barrier and thus bring about thermal hysteresis for the first-order magnetic transition. The magnetic transition-induced lattice distortion is more easily accommodated in the regions close to secondary phases and grain boundaries, where the atomic arrangement is more disordered. As a result, the nucleation of the PM-FM transition is found to start from the defect areas. However, the secondary phases and grain boundaries pin the domain walls, which hinders the growth of the ferromagnetic phase. The pinning effect of the defects will increase the energy barrier, causing an increase in the thermal hysteresis and the critical driven field for the first-order PM-FM transition. As a consequence, in order to further optimize the magnetocaloric performance, more efforts should made on tailoring both the intrinsic (e.g., lattice discontinuity) and extrinsic (e.g., size and distribution of the secondary phases) factors dominating the first-order magnetic transition of Fe₂P-based alloys.