Double Transition Research Articles

Updated and novel limits on double beta decay and dark matter-induced processes in platinum

A 510 day long-term measurement of a 45.3 g platinum foil acting as the sample and high voltage contact in an ultra-low-background high purity germanium detector was performed at Laboratori Nazionali del Gran Sasso (Italy). The data was used for a detailed study of double beta decay modes in natural platinum isotopes. Limits are set in the range {mathcal {O}}(10^{14}{-} 10^{19}) years (90% C.L.) for several double beta decay transitions to excited states confirming, and partially extending existing limits. The highest sensitivity of the measurement, greater than 10^{19} years, was achieved for the two neutrino and neutrinoless double beta decay modes of the isotope ^{198}Pt. Additionally, novel limits for inelastic dark matter scattering on ^{195}Pt are placed up to mass splittings of approximately 500 keV. We analyze several techniques to extend the sensitivity and propose a few approaches for future medium-scale experiments with platinum-group elements.

Excellent double metal MXenes MoWC anode: The synergistic effect of molybdenum and tungsten transition metal

Double transition metal MXenes are highly desirable as anodes in ion batteries due to their larger capacitance compared to traditional single transition metal MXenes. This study investigates the effect of W and Mo on the electrochemical properties of MoWC and MoWCO2 as anodes in sodium-ion batteries, using density functional theory calculations. It is found that due to the difference in electronegativity, the double transition metal phase collects more electrons at the metal terminal than the single metal phase. This additional charge is activated and transferred to the outside of the first adsorption layer, leading to an extra Na adsorption layer. Based on this mechanism, the capacities of MoWC and MoWCO2 are determined to be 204.10 and 165.54 mAhg−1, respectively, exceeding the theoretical capacities of single metal MXenes Mo2C and W2C. Furthermore, the Na diffusion barriers in the MoWC monolayer are higher than those in the single metal phase, but they are still competitive, with values of 0.072 eV on the Mo layer and 0.055 eV on the W layer. These findings offer valuable insights for future investigations of double transition metal MXenes as potential anodes in ion batteries.

Collaborative activation mechanism in double transition metal MXenes anode: An effective method to improve the capacitance of sodium ion battery

Through theoretical calculations, it is found that anode materials with double transition metal terminals (VNbC, VTaC, and NbTaC) exhibit better performance than their single metallic phases. Compared with single metal phase, the maximum sodium adsorption capacities of VNbC, VTaC, and NbTaC increased by 75%, 37.5%, and 75%, respectively. In particular, the metal VNbC VTaC and NbTaC anodes not only have high theoretical capacitances of 601.85, 302.20 and 328.13 mAhg−1, but also have original low migration barriers with sodium atoms. Bader charge indicates that the large capacities originate from the difference in metal electronegativity, and this difference leads to a reduction in the charge contribution of transition metals in materials and the accumulation of excess electrons on the surface. These extra accumulated electrons can be transferred to the outside to form an additional negative electron cloud that stabilizes the formation of the second layer of sodium adsorption, and leading to a large theoretical capacitance. We named this phenomenon the “Collaborative Activation” mechanism of double transition metal MXenes. These interesting results show that MXene anodes composed of different metal terminals are powerful methods to improve anode performance. Therefore, it provides a powerful reference for the research of MXenes.

Robustness of higher-order interdependent networks

In recent years, the research of multilayer interdependent networks has become a hotspot in complex networks. However, most of the study is limited to describing pairwise interactions. The systems in the real world are usually networks with higher-order interactions consisting of three or more units, such as epidemic transmission and cooperative communication networks. To better reflect the complex networks in the real world, this paper introduces the higher-order structures in the network, that is, simplicial complexes. In this paper, we construct a theoretical model of a two-layer partial dependence network with simplicial complexes in which failures between nodes occur through the synergistic effects of pairwise and higher-order interactions. In this model, removing a node will cause all other nodes in the same simplex to be removed, and due to the dependency between the two networks, the failure of the node will spread through dependency links between the two networks. This process will occur recursively and eventually lead to the cascading process. We introduce percolation theory to study the robustness of the network and give the theoretical solutions of different properties of the network, such as the size of the mutually connected giant component (MCGC), percolation threshold, etc. We find that the density of the triangle and the dependent strength between the two networks affect the percolation behaviours of the network together. When the density of the triangle exceeds a certain value, the network shows a double transition.

Asymmetric inter-layer interactions induce a double transition of information spreading

In recent years, a unique double transition phenomenon was observed under an asymmetric interaction in the epidemic model, where there are two transitions in the phase diagram of the spreading range versus the transmission probability. However, whether the asymmetric interactions exist and induce the double transition of information spreading is not very clear. Based on the global Twitter network communication data analysis, we found that besides the symmetric effects, there are also asymmetric interactions between different continents, indicated by the asymmetric weights of information exchange. To understand how the asymmetry affects the spreading behaviors, we proposed an information spreading model on a synthetic two-layered network and quantified the asymmetric interactions between regions by asymmetric inter-layer transmission probabilities. Interestingly, our results reveal a double transition under a strong inter-layer asymmetry in the phase diagram, which is derived from an asynchronous outbreak within the two layers. In addition, we discovered that depending on the strength of asymmetry, the second transition could alter from continuous to discontinuous. Finally, we developed a theory with asymmetric interactions to explain the numerical results thoroughly. The findings of this work may shed some light on comprehending the information’s secondary outbreaks in the real world.

Double transition metal atoms supported on defective borophene as efficient electrocatalysts for nitrogen reduction: a theoretical study

Electrocatalytic nitrogen reduction reaction (NRR) provides a promising approach for ammonia production under mild conditions. Developing high efficiency catalysts is the key and challenge for their practical application. Here, we employ density functional theory (DFT) to design a series of transition metal double-atom catalysts (DACs) with defective β12-borophene (DB-Hij) as the substrate, namely TM2@DB-Hij, where TM = Sc∼Zn, Zr∼Rh (expect Tc) and Hf∼Os. Two potential candidate catalysts Zr2@DB-H12 and Hf2@DB-H12 were selected based on three screening strategy. DFT calculation shows that on the two DACs, NRR starts from an end-on adsorption configuration of N2 and proceeds via the enzymatic mechanism. These two DACs not only exhibit excellent catalytic activity, with the limiting potentials of -0.28 and -0.39 V, respectively, but also effectively suppress the competing hydrogen evolution reaction (HER). Moreover, the effects of two substrates on the catalytic performance of TM2@DB-H12 were also investigated. The existence of Ag(111) substrate prepared in the experiment reduced the activity of the designed DACs, while the NRR activity was improved when graphene was used to replace Ag(111). The present study indicates that the substrates affect the electrocatalytic performance of catalysts to a certain extent, which should be considered in future research.

Sensing of sulfur containing toxic gases with double transition metal carbide MXenes

Sensing of sulfur containing gases, such as hydrogen sulfide (H2S) and sulfur dioxide (SO2), on double transition metal carbide MXenes has been studied by means of density functional theory calculations. It is found that both H2S and SO2 strongly physisorbed on M2TiC2Tx (M = Mo, Cr; Tx = O, S, OH) monolayers. The adsorption of H2S is stronger in the case of oxygen termination, (Mo2TiC2O2, Cr2TiC2O2), whereas SO2 has stronger adsorption on sulfur terminated (Mo2TiC2S2, Cr2TiC2S2) monolayers. Binding characteristics of H2S and SO2 are further confirmed with Bader charge transfer, density of states, and charge density differences. Using a statistical thermodynamic analysis, the sensing mechanism of H2S and SO2 is studied under varied pressures and temperature conditions. By means of non-equilibrium Green's function calculations, the sensitivities of H2S and SO2 on the Mo2TiC2S2 monolayer are found to be 16.3%, 10.3%, respectively, which showed promising sensing characteristics. Our results reveal that double transition metal carbide MXenes can be a potential candidate for the sensing of sulfur containing gases.

Ti3−yNbyC2Tx MXenes as high-rate and ultra-stable electrode materials for supercapacitors

Despite being a promising supercapacitor electrode material, the development of Ti3C2Tx has still been limited by many obstacles, such as restacking Ti3C2Tx nanosheets and non-electrochemically active fluorine terminations on the surface. Herein, new double transition metal Ti3−yNbyC2Tx MXenes are prepared by etching Ti3−yNbyAlC2 solid solution MAX precursors obtained by self-propagating high-temperature synthesis method for the first time. The synthesized Ti3−yNbyC2Tx MXenes exhibit larger interlayer spacing and more surface -O terminations than Ti3C2Tx, resulting in superior rate performance and high cycling stability as supercapacitors electrode materials. In particular, Ti2.9Nb0.1C2Tx demonstrates a high volumetric specific capacity of 1014 F cm−3 at a scan rate of 2 mV s−1, superior rate performance with a volumetric specific capacity of 422 F cm−3 at a scan rate of 2000 mV s−1, and ultra-long cycling life up to 84000 cycles at a current density of 10 A g−1. This work expands the practical applicability of the MXenes family in energy storage applications and provides a promising strategy to tailor the MXenes interlayer structure and surface chemistry.

Strain effects on the electronic and magnetic properties of Cr2TaC2 and Cr2TaC2O2 monolayers

Double transition metal MXene materials, such as Cr2TiAlC2, were successfully synthesized recently in addition to the synthesized mono transition metal MXenes. The physical and chemical properties of the MXenes can be tuned by varying the middle metal layer composition by other metal atoms. Thus, the desired mechanical, electronic, thermal, or magnetic properties can be revealed in that MXene material. The other method to tune material properties is by applying external strain on the structure. In this study, we systematically investigate the physical properties, such as dynamical, thermal, mechanical stability, electronic, and magnetic properties of the Cr2TaC2 and the Cr2TaC2O2 MXene monolayers for equilibrium and under biaxial strain. We find that both of MXene monolayers are energetically, thermally, and dynamically stable for certain compressive and tensile strain values. The Cr2TaC2 and the Cr2TaC2O2 MXene monolayers have a ferromagnetic ground state and show a metallic character in an equilibrium state and preserve it up to high tensile strain (ε = 0.10) value. The robust ferromagnetism above room temperature is demonstrated for the Cr2TaC2 with a Curie temperature of 714 K for the strain-free case. This value reduces to 234 K for the Cr2TaC2O2 monolayer. Moreover, our detailed Monte Carlo simulations reveal that the magnetic transition temperature of the system and also hysteresis properties can be controlled by moving from compressive to tensile strain ratios.

Synthesis and lithium ion storage performance of novel two dimensional vanadium niobium carbide (VNbCTx) MXene

Two-dimensional double transition metal carbides/nitride with unique out-of-plane arrangement of two metal atoms is emerging as a new pseudocapacitor material and attracting wide attention in the field of energy storage. Herein, fabrication of a novel 211-phase vanadium niobium carbide (VNbCTx) MXene by selectively etching the Al atomic layer from its VNbAlC MAX phase is reported for the first time. Effect of etching parameters on the microstructure, crystallinity, and electrochemical property of multilayer VNbCTx is examined. As the electrode material of lithium ion batteries, VNbCTx show a higher specific capacity of 520.5 mAh g−1 at 0.1 A g−1 and promising cycle stability. This work provides additional understanding about the synthesis and storage performance of double transition metal MXene, which will benefit the development of novel double transition metal MXene for energy storage applications.

The energy transition and green mineral value chains: Challenges and opportunities for Africa and Latin America

ABSTRACT There is growing momentum to address climate change and other environmental challenges through a ‘green energy transition’, that is, a shift from fossil fuel-based energy sources to renewable sources such as wind and solar. To carry out this global transition, a variety of resources – particularly minerals such as copper, lithium or cobalt – are required, and these are primarily extracted in the ‘Global South’. This means that these resource-rich countries face a double transition: the transition in their energy supplies, and the transition in their mining sectors. This special issue brings together different perspectives on the green energy transition and mineral value chains from Latin America and Africa. The articles investigate challenges for these countries, but also the opportunities that could potentially unfold as part of these far-reaching changes.

In situ transmogrification of nanoarchitectured Fe-MOFs decorated porous carbon nanofibers into efficient positrode for asymmetric supercapacitor application

In situ transmogrification is one of the most promising ways to synthesize positrode materials using a chemical treatment approach under optimal conditions for supercapacitor applications. The nickel salt concentration plays a vital role in the complete transmogrification of Fe-MOFs@PCNFs into Ni-Fe-OH@PCNFs (positrode). Herein, we successfully transform the tetragonal Fe-MOFs@PCNFs structure into pellet-like Ni-Fe-OH@PCNFs via in situ transmogrification under fixed temperature and pressure. The obtained Ni-Fe-OH@PCNFs-1 possess a unique porous architecture with a large surface area (74.3 m2g−1), which facilitates ion relocation and electron movement within the materials during charging/discharging. Owing to the limited surface area of electroactive materials, the double transition metal hydroxides (Ni-Fe-OH@PCNFs-D) synthesized directly (i.e., by employing two metal salts instantaneously) suffer a rapid decline in capacitance during cyclic stability test. The Ni-Fe-OH@PCNFs-1 electrode generated from Fe-MOFs@PCNFs has excellent cycling stability with ~86.7% capacitance retention and ~ 91.3% coulombic efficiency after 10,000 cycles at 10 A g−1. It also exhibits a remarkable specific capacitance of 1528 F g−1 at 1 A g−1. Additionally, the asymmetric supercapacitors (Ni-Fe-OH@PCNFs-1//Fe2O3/NPC@PCNFs) exhibit a maximum energy density of 44.3 Wh kg−1 at a power density of 907 W kg−1). The results of this work suggest the possibility of using MOF-derived nanoporous electrode materials and additional transition metal hydroxides for supercapacitors.

Quasinormal modes and phase structure of regular AdS Einstein–Gauss–Bonnet black holes

In this paper, we present an exact regular black hole solution in Einstein–Gauss–Bonnet coupled with nonlinear matter fields. It is a generalization of a regular Einstein–Gauss–Bonnet black hole in [Formula: see text] [Formula: see text] spacetime. The causal structure of the obtained solution identifies with Boulware–Deser black hole solution, except for the curvature singularity at the center. It incorporates the Boulware–Deser black holes in the absence of deviation parameters. We also study the thermodynamic properties of the solution that satisfies a modified first law of thermodynamics. Furthermore, we discuss the stability of the obtained black hole solution and, in this regard, a double phase transition occurs. Within this context, we find that phase transition exists at the point where the heat capacity diverges and, incidentally, the temperature attains the maximum value. We discuss the fluid nature of the black hole also exhibiting critical points. The quasinormal modes of the black hole solution and their dependencies on Gauss–Bonnet coupling and deviation parameters are also analyzed in terms of null geodesics.

Microwave measurements, calculations, and analysis for the gas phase ammonia-formic acid dimer

The gas-phase doubly hydrogen-bonded formic acid-ammonia complex was obtained by heating a sample of ammonium formate in neon. High-level DFT and MP2 calculations with various basis sets were performed and barriers for proton tunneling and internal rotation were determined. The microwave spectrum was measured in the 7–16 GHz frequency range using a Flygare-Balle type pulsed beam Fourier transform microwave (FTMW) spectrometer. Double resonance transitions were observed near 20 GHz. Rotational transitions were measured and fitted for two vibrational states to obtain the rotational constants and quadrupole coupling constants. The rotational constants were determined to have the following values: A = 12017.0(2), B = 4337.331(2), and C = 3227.279(2) for the 0+ state and A = 12017.0, B = 4302.02(1), and C = 3238.161(1) for the 0− state and have been fit to 16 transitions and 9 transitions respectively. Each state was fit to a rigid model showing quadrupole splitting and compared with computations.

High-Tc 1D Phase-Transition Semiconductor Photoluminescent Material with Broadband Emission.

One dimensional (1D) organic-inorganic halide hybrid perovskites have the advantages of excellent organic cation modifiability and diversity of inorganic framework structures, which cannot be ignored in the development of multi-functional phase-transition materials in photoelectric and photovoltaic devices. Here, we have successfully modified and synthesized an organic-inorganic hybrid perovskite photoelectric multifunctional phase-transition material: [C7 H13 ONCH2 F]⋅PbBr3 (1). The synergistic effect of the order double disorder transition of organic cations and the change of the degree of distortion of the inorganic framework leads to its high temperature reversible phase-transition point of Tc =374 K/346 K and its ultra-low loss high-quality dielectric switch response. Through in-depth research and calculation, compound 1 also has excellent semiconductor characteristics with a band gap of 3.06 eV and the photoluminescence characteristics of self-trapped exciton (STE) broadband emission. Undoubtedly, this modification strategy provides a new choice for the research field of organic-inorganic hybrid perovskite reversible phase-transition photoelectric multifunctional materials with rich coupling properties.

Two-dimensional transition metal carbide (Ti0.5V0.5)3C2Tx MXene as high performance electrode for flexible supercapacitor

MXenes have gained widespread interest in flexible supercapacitor due to their rich electrochemical activity and free-standing electrode structure. However, it has been a challenge to obtain an electrode with high (mass and volumetric) specific capacitance, high rate and long cycle life simultaneously. Herein, we have prepared a novel few-layer double transition metal carbide (Ti0.5V0.5)3C2Tx MXene. Multivalent V atoms with high electrochemical activity were constructed in stable M3C2-type MXene to obtain the (Ti0.5V0.5)3C2Tx electrode with excellent performance in flexible supercapacitors. The (Ti0.5V0.5)3C2Tx film has an excellent specific capacitance of 387F g−1 (1625 mF cm−3) at 1.0 A g−1, and 267 F g−1 (1121 mF cm−3) even at a high current density of 20.0 A g−1, demonstrating superior rate performance (69%). Moreover, the capacitance of the (Ti0.5V0.5)3C2Tx film remains stable during 100,000 cycles. The symmetric supercapacitor assembled using (Ti0.5V0.5)3C2Tx film has high energy and power densities, up to 5.6 Wh kg−1 and 5210.3 W kg−1. And the all-solid-state (Ti0.5V0.5)3C2Tx flexible SC maintains stable electrochemical performance after 200 bending cycles. This work shows the huge potential of (Ti0.5V0.5)3C2Tx in flexible supercapacitor, and provides a new idea for the design of high performance flexible electrodes.

In-situ partial oxidation of TiVCTx derived TiO2 and V2O5 nanocrystals functionalized TiVCTx MXene as anode for lithium-ion batteries

Two-dimensional double transition metal carbides or nitrides (MXenes) have been commonly concerned in the field of energy storage due to their distinctive structure and high conductivity. MXene-based electrode materials with single metal component are difficult to achieve high specific capacity, efficient ion/electron transport and stability, which hinder its practical application. Herein, we proposed a strategy by using in situ partial oxidation of double transition metal MXene (TiVCTx) derived TiO2 and V2O5 nanocrystals blends functionalized TiVCTx MXene (for simplicity denoted as TiVC@VTO) as electrode materials to boost the lithium ion battery performance. Effect of annealing temperature on the microstructure, crystallinity, and electrochemical property of TiVC@VTO is investigated. The TiVC@VTO retains the layer structure of the original TiVCTx MXene and at the same time the composition and microstructure can be regulated by a simple thermal annealing treatment to modify the oxidation degree. Compared with pristine TiVCTx, the oxidized sample demonstrates an optimal performance with specific capacity of 331.1 mAh g−1 after 100 cycles at current density of 0.1 A g−1 and 237.6 mAh g−1 after 1000 cycles at current density of 1.0 A g−1 at 500 °C (TiVC@VTO-500). Our work offers a simple and practicable method for enhanced lithium-ion storage capability by using double transition metal MXene. Moreover, this work also provides further information about the stability of TiVCTx MXene, which will benefit energy storage in the future development of novel double transition metal MXene materials for energy storage applications.

Induced diffusion percolation model: Examining the role of superactive nodes in the diffusion of innovations

Building on a recent study on scientific collaboration networks, we propose an induced diffusion percolation model that brings superactive nodes into focus. Defined as active nodes surrounded by at least k active or superactive neighbors, superactive nodes play a key role in innovation diffusion by inducing their neighbors to adopt an innovation. We investigate the induced diffusion percolation model using the modified Newman–Ziff algorithm on two-dimensional lattices (square and triangular lattices) and regular random networks with and without clustering. The induction by superactive nodes leads to a first-order percolation phase transition in two-dimensional lattices and a double transition – a continuous percolation transition followed by a discontinuous jump of the order parameter of the largest cluster’s strength – in regular random networks. Whereas clustering increases the percolation threshold in the classical percolation model on regular random networks, it decreases the critical initial activation probability that triggers a discontinuous jump of the induced activation.

Miniaturized double transit magnetic field measurement probe using the Faraday rotation principle.

This paper presents the design and experimental results of a double transit magnetic field measurement probe based on the Faraday rotation principle using terbium doped borosilicate glass as a sensor element. When the magnetic field is applied in the direction of propagation of light through the glass, the Faraday effect produces non-reciprocal circular birefringence. This property of the Faraday effect adds rotations when the light beam is reflected using a mirror placed at the other end of the glass and passed through the glass, making double transit of light through the sensor element. Experiments were carried out to verify the characteristics of the designed probe by inserting it inside the solenoid load coil. The Verdet constant of the glass is determined using the slope of the linear least-squares fitted curve between the Faraday rotation angle and the applied magnetic field, obtained as 89.22r a d/(T⋅m) with a relative uncertainty of 2.43%. The magnetic field was measured with 0.28% accuracy. In the optics experiments, alignment of components is the major task. To the authors' knowledge, this is the first of its kind double transit miniaturized magnetic field measurement probe configuration in which components are aligned inside the single probe structure. The probe is easily portable and can be used in inaccessible locations in various applications such as accelerators, Z/θ pinch devices, or fusion reactors such as tokamaks, in which the magnetic field is one of the main parameters.

Atomically selective oxidation of (Ti,V) MXene to construct TiO2@TiVCTx heterojunction for high-performance Li-ion batteries

In situ derivation of TiO2 from Ti2CTx and Ti3C2Tx MXenes is a promising strategy to construct TiO2-based heterostructure. How to precisely control the conversion depth of MXene and well maintain its lamellar structure are the top priority. Herein, double transition metal (Ti, V) MXenes (Ti2−yVyCTx) act as precursors to engineer TiO2/MXene heterostructure as anode materials for lithium-ion batteries. Due to the different oxidation tendency, vanadium atoms with higher oxidative tolerance can maintain the 2D lamella morphology and high electronic conductivity while titanium atoms can be selectively oxidized to well-dispersed TiO2 nanoparticles. Moreover, the content and dispersity of derived TiO2 nanoparticles can be well controlled by adjusting the molar ratio of Ti/V in the Ti2−yVyCTx precursors. The intensive interfacial interaction between derived TiO2 and vanadium dominated MXene layers protects TiO2 nanoparticles from pulverization and detachment from 2D MXene as well as the restacking of MXene layers during charge/discharge cycles. Benefiting from the synergistic effects, the TiO2@TiVCTx anode delivers a superior specific capacity of 741.2 mAh g−1 at 0.1 A g−1, which shows prominent advantage in current MXene-derived anode materials. This work innovatively realizes atomically selective oxidation of double metal transition MXenes and regulate the derivatives for high performance anode materials.