Polar Metal Research Articles

Broken Inversion Symmetry in Van Der Waals Topological Ferromagnetic Metal Iron Germanium Telluride.

Inversion symmetry breaking is critical for many quantum effects and fundamental for spin-orbit torque, which is crucial for next-generation spintronics. Recently, a novel type of gigantic intrinsic spin-orbit torque is established in the topological van der Waals(vdW) magnet iron germanium telluride. However, it remains a puzzle because no clear evidence exists for interlayer inversion symmetry breaking. Here, the definitive evidence of broken inversion symmetry in iron germanium telluride directly measured by the second harmonic generation (SHG) technique is reported. The data show that the crystal symmetry reduces from centrosymmetric P63/mmc to noncentrosymmetric polar P3m1 space group, giving the threefold SHG pattern with dominant out-of-plane polarization. Additionally, the SHG response evolves from an isotropic pattern to a sharp threefold symmetry upon increasing Fe deficiency, mainly due to the transition from random defects to ordered Fe vacancies. Such SHG response is robust against temperature, ensuring unaltered crystalline symmetries above and below the ferromagnetic transition temperature. These findings add crucial new information to the understanding of this interesting vdW metal, iron germanium telluride: band topology, intrinsic spin-orbit torque, and topological vdW polar metal states.

Transforming a strain-stabilized ferroelectric into an intrinsic polar metal with light

Transforming a strain-stabilized ferroelectric into an intrinsic polar metal with light

Room-Temperature, Current-Induced Magnetization Self-Switching in A Van Der Waals Ferromagnet.

2D layered materials with broken inversion symmetry are being extensively pursued as spinsource layers to realize high-efficiency magnetic switching. Such low-symmetry layered systems are, however, scarce. In addition, most layered magnets with perpendicular magnetic anisotropy show a low Curie temperature. Here, the experimental observation of spin-orbit torque magnetization self-switching at room temperature in a layered polar ferromagnetic metal, Fe2.5 Co2.5 GeTe2 is reported. The spin-orbit torque is generated from the broken inversion symmetry along the c-axis of the crystal. These results provide a direct pathway toward applicable 2D spintronic devices.

Effect of femtosecond laser processing atmosphere on micro-nano structures and wetting properties of Ti6Al4V surface

Femtosecond laser processing was carried out to build the hydrophobic micro-nano structure on Ti6Al4V titanium alloy, and the effect of processing atmosphere, i.e., air and nitrogen, on the geometric dimension feature, distribution, element content, and the hydrophobic property was investigated. Results showed that the disordered micro-hump structure was induced in air, while micro-spindle structure with regular geometrical morphology formed in nitrogen. The size of micro-nano structure induced in air is larger than that in nitrogen, and both of them increased with the laser energy density. The micro-hump structure surface induced in air exhibited better hydrophobicity (water contact angle of 144.6°) than that in nitrogen. Processing in nitrogen could effectively inhibit the oxidation of the micro-nano structure, providing a breakthrough to improve the surface hydrophobic stability by reducing the micro-nano structure size and the surface polar metal oxides.

Corrosion inhibition of extracts from the expired traditional Chinese patent medicines for Q235 carbon steel in hydrochloric acid

During the COVID-19 epidemic, traditional Chinese patent medicine played a significant role in treatment and prevention. However, excessive production of medicines will face serious disposal problems once they are expired, and how to achieve safe and efficient utilization of resources becomes another challenge. In this study, the diverse organic components of traditional Chinese patent medicine-YanReQing Granules (YGE) have been extracted and enriched using a low-temperature extraction method, and the main compositions have been analyzed by liquid chromatography-mass spectrometry (LC-MS). The inhibition performance of YGE for Q235 steel in 0.1 mol L−1 HCl solution was evaluated by various methods. The results indicated that the corrosion rate of metal decreased significantly with the addition of YGE, and the corrosion potential shifted positively as the increase of cathodic and anodic Tafel slopes, indicating that the YGE belongs to a mixed type of corrosion inhibitor with the simultaneously inhibition on cathode and anode. The inhibition efficiency of YGE increased gradually with the more additive amounts, and exceeded 99% calculated by the fitting current density in polarization curves. The active ingredients in YGE are mainly composed of hydroxyl and carbon-based aromatic hydrocarbons, which are easily protonated in hydrochloric acid solution and carry a positive charge, and then adsorb at the metal interface electrostatically to form a shielding layer. Moreover, the theoretical calculations have confirmed that the chemical adsorption can be achieved between the polar atoms and metal to enhance the protective layer ultimately.

Effect of Phenolics from Aeonium arboreum on Alpha Glucosidase, Pancreatic Lipase, and Oxidative Stress; a Bio-Guided Approach.

Metabolic syndrome (MetS) is a global issue affecting over a billion people, raising the risk of diabetes, cardiovascular disorders, and other ailments. It is often characterized by hypertension, dyslipidemia and/or obesity, and hyperglycemia. Chemical investigation of Aeonium arboreum (L.) Webb & Berthel led to the isolation of six compounds, viz. β-sitosterol, β-sitosterol glucoside, myricetin galactoside, quercetin rhamnoside, kaempferol rhamnoside, and myricetin glucoside. Interestingly, A. arboreum's dichloromethane (DCM), 100 and 50% MeOH Diaion fractions and the isolated compound (quercetin-3-rhamnoside) revealed potent α-glucosidase inhibitory activity, especially 50% Diaion fraction. In addition, they also showed very potent antioxidant potential, especially the polar fractions, using DPPH, ABTS, FRAP, ORAC, and metal chelation assays. Notably, the 50% Diaion fraction had the highest antioxidant potential using DPPH and ORAC assays, while the 100% Diaion fraction and quercetin-3-rhamnoside showed the highest activity using ABTS, FRAP, and metal chelation assays. Also, quercetin-3-rhamnoside showed a good docking score of -5.82 kcal/mol in comparison to acarbose. In addition, molecular dynamic stimulation studies illustrated high stability of compound binding to pocket of protein. Such potent activities present A. arboreum as a complementary safe approach for the management of diabetes mellitus as well as MetS.

Designing ferromagnetic polar half-metals in short-period perovskite nickelates

ABO3 perovskites oxides show fascinating functional properties, including ferroelectricity, magnetism, metal-to-insulator transition, half metallicity, polar metallic phase, etc. In particular, rare earth nickelates and alkaline earth nickelates within the orthorhombic crystal structures show an insulator–metal transition (IMT) and half-metallic (HM) nature respectively. Here, we report a series of ferromagnetic polar half metals by constructing LnNiO3/CaNiO3 short period 1/1 superlattices (SLs) with Ln = La, Nd, Gd, Dy, Tm, and Lu within an orthorhombic phase. The polar distortion is induced by a hybrid-improper ferroelectric mechanism i.e., by constructing Ln/Ca layer-ordering. The system shows a ferromagnetic Ni-Ni interaction, whereas Ni-3d’s are interacting antiferromagnetically with O-2p. We explain that the origin of observed half metallicity and ferromagnetism is due to strong hybridization between Ni-3d and O-2p near the Fermi level and double exchange mechanism, respectively.

Quantum fluctuation of ferroelectric order in polar metals

The polar metallic phase is an unusual metallic phase of matter containing long-range ferroelectric (FE) order in the electronic and atomic structure. Distinct from the typical FE insulating phase, this phase spontaneously breaks the inversion symmetry without global polarization. Unexpectedly, the FE order is found to be dramatically suppressed and destroyed at moderate ~ 10% carrier density. Here, we propose a general mechanism based on carrier-induced quantum fluctuations to explain this puzzling phenomenon. The quantum kinetic effect would drive the formation of polaronic quasi-particles made of the carriers and their surrounding dipoles. The disruption in dipolar directions can therefore weaken or even destroy the FE order. We demonstrate such polaron formation and the associated FE suppression via a concise model using exact diagonalization, perturbation, and quantum Monte Carlo approaches. This quantum mechanism also provides an intuitive picture for many puzzling experimental findings, thereby facilitating new designs of multifunctional FE electronic devices augmented with quantum effects.

Clues to potential dipolar-Kondo and RKKY interactions in a polar metal

The coexistence of electric dipoles and itinerant electrons in a solid was postulated decades ago, before being experimentally established in several ‘polar metals’ during the last decade. Here, we report a concentration-driven polar-to-nonpolar phase transition in electron-doped BaTiO3. Comparing our case with other polar metals, we find a particular threshold concentration (n*) linked to the dipole density (nd). The universal ratio frac{{n}_{{{{rm{d}}}}}}{{n}^{* }}approx 8.0(6) suggests a common mechanism across different polar systems, possibly explained by a dipolar Ruderman-Kittel-Kasuya-Yosida theory. Moreover, in BaTiO3, we observe enhanced thermopower and upturn on resistivity at low temperatures near n*, resembling the Kondo effect. We argue that local electric dipoles act as two-level-systems, whose fluctuations couple with surrounding electron clouds, giving rise to a potential dipolar-counterpart of the Kondo effect. Our findings unveil a mostly uncharted territory for exploring emerging physics associated with electron-dipole correlations, encouraging further theoretical work on dipolar-RKKY and Kondo interactions.

Strong electron-phonon coupling driven pseudogap modulation and density-wave fluctuations in a correlated polar metal

There is tremendous interest in employing collective excitations of the lattice, spin, charge, and orbitals to tune strongly correlated electronic phenomena. We report such an effect in a ruthenate, Ca3Ru2O7, where two phonons with strong electron-phonon coupling modulate the electronic pseudogap as well as mediate charge and spin density wave fluctuations. Combining temperature-dependent Raman spectroscopy with density functional theory reveals two phonons, B2P and B2M, that are strongly coupled to electrons and whose scattering intensities respectively dominate in the pseudogap versus the metallic phases. The B2P squeezes the octahedra along the out of plane c-axis, while the B2M elongates it, thus modulating the Ru 4d orbital splitting and the bandwidth of the in-plane electron hopping; Thus, B2P opens the pseudogap, while B2M closes it. Moreover, the B2 phonons mediate incoherent charge and spin density wave fluctuations, as evidenced by changes in the background electronic Raman scattering that exhibit unique symmetry signatures. The polar order breaks inversion symmetry, enabling infrared activity of these phonons, paving the way for coherent light-driven control of electronic transport.

Beaded CoSe2-C Nanofibers for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are regarded as highly promising energy storage devices due to their high theoretical specific capacity and high energy density. Nevertheless, the commercial application of Li-S batteries is still restricted by poor electrochemical performance. Herein, beaded nanofibers (BNFs) consisting of carbon and CoSe2 nanoparticles (CoSe2/C BNFs) were prepared by electrospinning combined with carbonization and selenization. Benefitting from the synergistic effect of physical adsorption and chemical catalysis, the CoSe2/C BNFs can effectively inhibit the shuttle effect of lithium polysulfides and improve the rate performance and cycle stability of Li-S batteries. The three-dimensional conductive network provides a fast electron and ion transport pathway as well as sufficient space for alleviating the volume change. CoSe2 can not only effectively adsorb the lithium polysulfides but also accelerate their conversion reaction. The CoSe2/C BNFs-S cathode has a high reversible discharge specific capacity of 919.2 mAh g-1 at 0.1 C and presents excellent cycle stability with a low-capacity decay rate of 0.05% per cycle for 600 cycles at 1 C. The combination of the beaded carbon nanofibers and polar metal selenides sheds light on designing high-performance sulfur-based cathodes.

Phonon-induced collective modes in spin-orbit coupled polar metals

Phonon-induced collective modes in spin-orbit coupled polar metals

Electronic characteristic, tensile cracking behavior and potential energy surface of TiC(111)/Ti(0001) interface: A first‑principles study

The preparation of TiC coating on Ti alloy surface to improve the wear resistance has attracted attention from researchers in aerospace field. The service life of TiC coating is related to the interfacial adhesion properties between TiC coating and Ti alloy substrate. However, it is difficult to explain its interfacial adhesion mechanism by experimental methods. Based on the termination of atoms on the TiC surface, two TiC/Ti interface models named as the C-terminated-TiC(111)/Ti(0001) and Ti-terminated-TiC(111)/Ti(0001) interface were constructed by first-principles. The interfacial electronic characteristic of C—Ti bond is a mixture of polar covalent and metal bonds, and that of Ti—Ti bond is the metal bond. The tensile strains of both C-terminated-TiC(111)/Ti(0001) and Ti-terminated-TiC(111)/Ti(0001) interface in the fracture stage are ranged from 12% to 14%. Their maximum tensile stresses are 16.201 GPa and 15.590 GPa, respectively. The sliding potential energy surface maximum of C-terminated-TiC(111)/Ti(0001) and Ti-terminated-TiC(111)/Ti(0001) interface are 5.387 J/m2 and 0.271 J/m2, respectively. And the sliding potential barriers on the minimum energy path are 2.094 J/m2 and 0.136 J/m2 with an ideal shear strength of 20.32 GPa and 1.61 GPa, respectively. In summary, the interfacial adhesion property of C-terminated-TiC(111)/Ti(0001) interface is better than that of Ti-terminated-TiC(111)/Ti(0001) interface.

Fully fluorinated hybrid zeolite imidazole/Prussian blue analogs with combined advantages for efficient oxygen evolution reaction

Hybrid metal-organic framework (MOF) derivatives play a significant role in the novel catalyst development in energy conversion reactions. Here, we demonstrated the low-temperature fully fluorinated zeolitic imidazole framework (ZIF) coupled with a three-dimensional open framework Prussian blue analog (PBA) with combined advantages for electrocatalytic oxygen evolution reaction (OER) in water splitting reaction. The spectroscopic analysis and the electrochemical studies revealed the combined advantages of efficient electronic effect and active site synergism. Because of good conductivity improvement by N-doped carbon derived from ZIF and the high electrochemical surface area and active site exposure from PBA derivatives, good catalytic performance was obtained on the optimal catalyst of CoNi ZIF/CoFe-PBA-F-300, which required a low overpotential of 250 mV to reach 10 mA/cm2 loaded on the glassy carbon electrode, with Tafel slope of 47.4 mV/dec, and very high dynamic and steady stability. In addition, the multi-component with the mixed structure from highly polar metal fluorides promoted the easy formation of the active phase as revealed by the post-sample analysis. The current results showed a novel composite catalyst materials development from the hybrid MOF derivatives, which would be promising in the electrolysis of water oxidation reactions and energy-relevant catalysis reactions.

Differential depression of calcium lignosulfonate on chalcopyrite and molybdenite flotation with collector kerosene

Molybdenite is the main mineral for molybdenum extraction, which coexists with chalcopyrite in porphyry copper deposits. However, the separation of molybdenite from chalcopyrite by flotation uses large amounts of toxic depressants, causing financial, health and environmental concerns. In this study, an environmentally friendly depressant, calcium lignosulfonate, with a low price was explored to depress chalcopyrite in the presence of kerosene, a collector widely used to float molybdenite. Adsorption isotherms of calcium lignosulfonate on chalcopyrite and molybdenite surfaces and contact angles of chalcopyrite, molybdenite’s basal planes and edge planes in the absence and presence of calcium lignosulfonate and kerosene were determined to understand the adsorptions of calcium lignosulfonate on heterogeneous chalcopyrite and molybdenite surfaces and the subsequent interactions with kerosene. It was found that calcium lignosulfonate effectively depressed chalcopyrite flotation, but had little depression effect on molybdenite because the adsorption density of calcium lignosulfonate on chalcopyrite was significantly higher than that on molybdenite. Calcium lignosulfonate molecules were uniformly adsorbed on chalcopyrite and molybdenite despite the heterogeneous surfaces. In fact, calcium lignosulfonate adsorbed on polar metal ion sites of chalcopyrite surfaces, blocking the adsorption of kerosene from adsorbing on hydrophobic sulphur-rich phases. Analogously, calcium lignosulfonate adsorbed on polar edge planes of molybdenite with little interference with the adsorption of kerosene on hydrophobic basal planes.

REMOVAL OF SULPHUR-CONTAINING COMPOUNDS FROM THE DIESEL FRACTION BY EXTRACTION SYSTEMS BASED ON COORDINATING POLAR SOLVENTS AND METAL SALTS

The process of removing sulphur-containing compounds from the diesel fraction has been carried out and investigated. The systems based on coordinating polar solvents (DMF and DMSO) and metal salts (CuCl2, CoCl2, MnCl2, Mn(TFA)2, Cu(TFA)2) were used as extractants. It has been established that the presence of metal salts in extraction systems increases the degree of removal of sulphur-containing compounds from the diesel fraction from 11 to 49 % and reduces the content of polycyclic aromatic hydrocarbons by 33 %. It is assumed that the addition of metal salts to the solvent enhances its acceptor properties, which is manifested in the enhancement of its extractability.

Optimally arranged TiO2@MoS2 heterostructures with effectively induced built-in electric field for high-performance lithium-sulfur batteries

To overcome the serious technological issues affecting lithium-sulfur (Li-S) batteries, such as sluggish sulfur redox kinetics and the detrimental shuttle effect, heterostructure engineering has been investigated as a strategy to effectively capture soluble lithium polysulfide intermediates and promote their conversion reaction by integrating highly polar metal oxides with catalytically active metals sulfides. However, to fully exploit the outstanding properties of heterostructure-based composites, their detailed structure and interfacial contacts should be designed rationally. Herein, optimally arranged TiO2 and MoS2-based heterostructures (TiO2@MoS2) are fabricated on carbon cloth as a multifunctional interlayer to efficiently trap polysulfide intermediates and accelerate their redox kinetics. Owing to the synergistic effects between TiO2 and MoS2 and the uniform heterointerface distribution that induces the ideally oriented built-in electric field, Li-S batteries with TiO2@MoS2 interlayers exhibit high rate capability (601 mA h g−1 at 5 C), good cycling stability (capacity-fade rate of 0.067% per cycle over 500 cycles at 2 C), and satisfactory areal capacity (5.2 mA h cm−2) under an increased sulfur loading of 5.2 mg cm−2. Moreover, by comparing with a MoS2@TiO2 interlayer composed of reversely arranged heterostructures, the effect of the built-in electric field’s direction on the electrocatalytic reactions of polysulfide intermediates is thoroughly investigated for the first time. The superior electrocatalytic activities of the rationally arranged TiO2@MoS2 interlayer demonstrate the importance of optimizing the built-in electric field of heterostructures for producing high-performance Li-S batteries.

Theory of criticality for quantum ferroelectric metals

Although ferroelectricity in metals was long considered to be impossible, a large family of materials hosting both states has been discovered in recent years, and these properties are often strongly coupled. The authors investigate here the quantum phase transition between the ferroelectric and paraelectric states in metals. They find unique quantum critical properties stemming from unconventional inversion-breaking fluctuations, along with enhanced tendencies to both spin singlet and triplet superconductivity, and provide protocols for strain control of the quantum state of these systems.

Polar Metals: Principles and Prospects

We review the class of materials known as polar metals, in which polarity and metallicity coexist in the same phase. While the notion of polar metals was first invoked more than 50 years ago, their practical realization has proved challenging since the itinerant carriers required for metallicity tend to screen any polarization. Huge progress has been made in the last decade, with many mechanisms for combining polarity and metallicity proposed and the first examples, LiOsO3 and WTe2, identified experimentally. The availability of polar metallic samples has opened a new paradigm in polar metal research, with implications in the fields of topology, ferroelectricity, magnetoelectricity, spintronics, and superconductivity. Here, we review the principles and techniques that have been developed to design and engineer polar metals and describe some of their interesting properties, with a focus on the most promising directions for future work.

The synergistic adsorption-catalysis research of highly efficient interlayer constructed from coal fly ash for superior lithium-sulfur batteries

The notorious shuttle effect severely limits the practical application of Lithium-Sulfur Batteries (LSBs). In line with the concept of “green chemistry”, industrial solid waste is reasonably applied to the design of battery’s interlayer. The modified coal fly ash (MCFA) can effectively accelerate the redox kinetics of the electrode and optimize the nucleation and decomposition of Li2S. The synergistic adsorption and catalytic action from rich pore structure and polar metal oxides can effectively capture and fix free polysulfide (LiPSs), which realizes the inhibition of shuttle effect. The LSBs with MCFA interlayer exhibit good cycle stability (decay-rate: 0.05% per cycle) and rate capability (703 mAh g−1 at 3C). Even under extreme conditions of poor electrolytes (E/S = 7.8 μL /mg), Cell-MCFA/PE with a high S loading (7.5 mg cm−2) still performs well (732 mAh g−1 after 100 cycles). This work provides an economical and environment-friendly strategy for the design of interlayer, which is conducive to the commercialization process of LSBs.