Volume Collapse Research Articles

Theoretical Study on BiCoO3: Pressure‐Tuned Transformation of Structure, Magnetism, Charge, and Spin State

AbstractThe atomic structures, electronic structures, magnetic properties, and spin states of BiCoO3 multiferroic material under hydrostatic pressure are comprehensively investigated by using first‐principles calculation based on density functional theory. Firstly, we found the pressure‐tuned structural symmetry transition from tetragonal P4 mm (No. 99) to cubic Pmm (No. 221) space group. The structural transformation prompts the Co─O polyhedral coordination transfer from a CoO5 pyramidal to a CoO6 distorted octahedron. Secondly, the pressure‐induced magnetic change from C‐type antiferromagnetic state to ferromagnetic state and then to paramagnetic configuration occurred after continuous compression of the volume. Essentially, the fundamental reason for the transition of the magnetic structure lies in the change of the internal atomic structure, such as the pressure induced abrupt changes of Co─O bond length and <Co─O─Co> bond angle. Meanwhile, an obvious volume collapse was observed when the pressure was applied to 51–56 GPa. Finally, as the pressure increases, the magnetism changes from C‐type antiferromagnetic state to paramagnetic configuration, accompanying the transformation from high spin state with b2g2eg2a1g1b1g1 configuration in pyramid structure to low spin state with t2g6eg0 in octahedral field. Therefore, our results demonstrate that applied hydrostatic pressure in BiCoO3 can trigger the transformation of structure, magnetism, charge, and spin state.

Ro2En: Robust Neural Environment Encoder for Domain Generalization of Fast Motion Planning

This paper discusses a new issue named domain generalization of fast motion planning in 3D environments, which benefits agility-required robot applications such as autonomous driving and uncrewed aerial vehicle obstacle avoidance flight. The existing work shows that conventional spatial search-based planning algorithms cannot meet the real-time requirement due to high time costs. The end-to-end neural network-based methods achieve an excellent balance between performance and planning speed in the seen environments, but are hard to transfer to new scenarios. To overcome this limitation, we propose a novel Robust Environment Encoder (Ro2En) approach to domain generalization of fast motion planning. Specifically, by demonstrating the reconstructed environment, we find that the previous environment encoder cannot encode the volume information properly, i.e., a volume collapse ensues, which leads to noisy environment modeling. Inspired by this observation, a dual-task auto-encoder is developed. It can not only reconstruct the point cloud of the obstacles, but also align their geometric centers. Experiment results showed that in the new scenarios, Ro2En outperformed previous state-of-the-art conventional and neural alternatives with a much smaller performance variation.

Inherent porosity of Zeolitic Imidazolate Framework-62 melt leading to formation of the porous melt-quenched glass

Porous glasses produced through melt-quenching of some selective metal organic frameworks like Zeolitic Imidazolate Framework-62 (ZIF-62) and ZIF-4 belong to the advanced functional materials because of their inherent porosity, ease of processing, high gas adsorption capacity and gas separation selectivity. We have delineated thermal induced modifications in the porosity features (pore size, size-distribution and pore density) of crystalline ZIF-62 from room temperature (RT) to its melt-state (> melting point, Tm) followed by its quenching, back to RT, carrying out the depth sensitive positron annihilation lifetime spectroscopy (PALS) measurements in-situ at varying temperatures (RT−Tm). On heating under vacuum, the pores' size as well as size-distribution of crystalline ZIF-62 increases up to ∼473 K as a consequence of removal of entrapped solvent molecules and nonuniform thermal expansion. At higher temperatures (∼473 −573 K), a reduction in pores’ size and size-distribution is observed due to the loss of long range ordering and volume collapse. On melting, ZIF-62 turns into a porous liquid having ∼1.4 times larger pores compared to its crystalline form. The quenching of this porous melt is fully irreversible, and results in the formation of a porous glass having the pores larger than its crystalline counterpart. The in-situ PALS investigation provides the first experimental evidence of inherent porosity in ZIF-62 melt existing at high temperature that has been predicted before through molecular dynamics simulation of the ZIFs-based melts.

Core-shell heterostructure Cu(OH)2@NiCoPO4 nanorod arrays constructed by electrochemical deposition for hybrid supercapacitor electrode material

Electrochemical deposition can be used to make three-dimensional nanoarray core-shell heterostructures that can effectively solve the issues of low rate performance and small capacity caused by agglomeration and morphological collapse. NiCo phosphates synthesized using conventional methods are susceptible to agglomeration and experience inevitable volume collapse during prolonged charging and discharging cycles. Core-shell heterostructures are created by electropositing lamellar NiCoPO4 on arrays of Cu(OH)2 nanorods. This structure shortens the ionic transport distance and preserves the excellent electrical conductivity of NiCoPO4, in addition to offering a greater surface area for the growth of NiCoPO4, increasing the reactive sites. Furthermore, electrodeposition can reduce material aggregation, enabling tight contact between NiCoPO4 and the Cu(OH)2 skeleton. This enhances the material's mechanical stability and successfully avoids the collapse issue. Results showed that the Cu(OH)2@NiCoPO4/CF composite demonstrated an elevated specific capacitance of 208.54 mAh g-1 at 1 A g-1, and it maintained 80.03 % of its original capacity after 10,000 cycles. The Cu(OH)2@NiCoPO4/CF//AC HSC device that was made showed great cycling stability, keeping 119.80 % of its charge after 30,000 charge/discharge cycles at 10 A g-1. It also offers an outstanding energy density of 52.16 Wh kg-1 (800.85 W kg-1). The electrochemical performance of bimetallic NiCo phosphates may be significantly enhanced by their structural design, offering new possibilities for the advancement of phosphates in electrode materials.

Pressure-induced phase transitions of ZrAl2 from first-principles calculations

Although ZrAl2 has been extensively studied, its structural features and properties under high pressures remain unclear. Using the CALYPSO structural search method combined with first-principles calculations, we investigated the structural evolution and mechanical stability of ZrAl2 at high pressures. Our research reveals that at 198 GPa, ZrAl2 undergoes a phase transition from the P63/mmc phase to the Pmmm phase. This transition results in a volume collapse of 2.1%, indicating a first-order phase change. A comprehensive analysis of the elastic constants and phonon spectra confirms the structural stability of four new phases of ZrAl2. Our research findings provide a comprehensive view of the structural evolution of ZrAl2 under high pressure. This valuable information enhances the understanding of the physical and chemical properties of C14-type ZrAl2 when subjected to high-pressure conditions.

Improving cycling performance of the NaNiO2 cathode in sodium-ion batteries by titanium substitution

O3-type layered oxide cathodes, such as NaNi0.5Mn0.5O2, have garnered significant attention due to their high theoretical specific capacity while using abundant and low-cost sodium as intercalation species. Unlike the lithium analog (LiNiO2), NaNiO2 (NNO) exhibits poor electrochemical performance resulting from structural instability and inferior Coulomb efficiency. To enhance its cyclability for practical application, NNO was modified by titanium substitution to yield the O3-type NaNi0.9Ti0.1O2 (NNTO), which was successfully synthesized for the first time via a solid-state reaction. The mechanism behind its superior performance in comparison to that of similar materials is examined in detail using a variety of characterization techniques. NNTO delivers a specific discharge capacity of ∼190 mAh g−1 and exhibits good reversibility, even in the presence of multiple phase transitions during cycling in a potential window of 2.0‒4.2 V vs. Na+/Na. This behavior can be attributed to the substituent, which helps maintain a larger interslab distance in the Na-deficient phases and to mitigate Jahn–Teller activity by reducing the average oxidation state of nickel. However, volume collapse at high potentials and irreversible lattice oxygen loss are still detrimental to the NNTO. Nevertheless, the performance can be further enhanced through coating and doping strategies. This not only positions NNTO as a promising next-generation cathode material, but also serves as inspiration for future research directions in the field of high-energy-density Na-ion batteries.

Enhancement of superconductivity and structural phase transitions under pressure in FeTe0.89S0.11

The ternary iron chalcogenide, FeTe0.89S0.11 is a prominent member of the family of Fe-based superconductors with an ambient pressure Tc of around 8 K and a simple structure formed by layers of edge-sharing distorted tetrahedra separated by a van der Waals gap. Upon compression to 6 GPa, the Tc increases monotonically to 11 K. The superconductivity disappeared at about 6 GPa which was correlated to a softening of a Raman mode. High-resolution synchrotron X-ray diffraction shows that the FeTe0.89S0.11 started to transform from the monoclinic phase described by space group Cm to a disordered triclinic phase described by space group P1 at around 10 GPa (theoretical) - 14 GPa (experimental). Due to the phase transition the studied material transforms from a layered compound to a polymer, which is accompanied by a volume collapse of 4.65 %, indicating a discontinuous first-order phase transition. The disappearance of Raman modes, along with pressure independent resistivity, and ab initio calculations results support the structural and electronics phase transition. According to our results Fe(Te,S) may be useful for future high-field power applications being formed of relatively inexpensive and nontoxic elements.

Structural behavior and electrical transport properties of Mg2Ge under high pressure

The structural and electrical transport properties are investigated from ambient pressure to 40 GPa for Mg2Ge using first-principles calculations and in situ high-pressure electrical experiments. Mg2Ge undergoes reversible phase transitions from anti-fluorite structure to anti-cotunnite structure and then to Ni2In-type structure by enthalpy calculations, both reflected in the cell volume collapse and discontinuous axial ratios of lattice constants. The inter- and intra-layer sliding of Mg and Ge atomic pairs is revealed induced by phase transitions. The metallization transition is determined by the energy-band closure, in good agreement with the enhancing metallic behavior experimentally evidenced above approximately 7 GPa according to the temperature-dependent resistivity measurement. The structural phase transitions are determined at around 9.6 GPa and 35.8 GPa based on discontinuous electrical parameters. The paper tends to shed light on the structural behaviors and electrical transport properties of intermetallic compounds Mg2X-type (X = IVA group elements) family under extreme conditions.

First-principles study of structural and electronic properties of multiferroic oxide Mn3TeO6 under high pressure

Abstract Mn3TeO6 (MTO) has been experimentally found to adopt a P21/n structure under high pressure, which exhibits a significantly smaller band gap compared to the atmospheric R3 phase. In this study, we systematically investigate the magnetism, structural phase transition and electronic properties of MTO under high pressure through first-principles calculations. Both R3 and P21/n phases of MTO are antiferromagnetic at zero temperature. The R3 phase transforms to the P21/n phase at 7.58 GPa, accompanied by a considerable volume collapse of about 6.47%. Employing the accurate method that combines DFT+U and G0W0, the calculated band gap of R3 phase at zero pressure is very close to the experimental values, while that of the P21/n phase is significantly overestimated. The main reason for this difference is that the experimental study incorrectly used the Kubelka-Munk plot for the indirect band gap to obtain the band gap of the P21/n phase instead of the Kubelka-Munk plot for the direct band gap. Furthermore, our study reveals that the transition from the R3 phase to the P21/n phase is accompanied by a slight reduction in the band gap.

Pressure-induced large volume collapse and possible spin transition in HP-PdF2-type FeCl2

Pressure-induced large volume collapse and possible spin transition in HP-PdF2-type FeCl2

Martensitic-like microstructures across the isostructural phase transitions in Cerium

The isostructural gamma–alpha phase transition in elemental cerium is an electronic transition caused by a delocalization of the 4f electrons. This affects the bonding properties of Ce atoms and leads to a large volume collapse reaching ∼17% in the low pressure regime (¡ 2 GPa). While great attention has been drawn on the electronic description of this transition, attempts to understand the mesoscale mechanisms of this structural transition and their consequences in terms of microstructure remain scarce. We have investigated this transition by means of combined X-ray Computed Tomography and Energy Dispersive X-ray Diffraction on polycrystalline samples. Our experimental observations reveal a platelet-shape microstructure across the transition and up to the critical point, which have been associated to displacive mechanisms. Based on continuum mechanics modeling and ab initio calculations, we propose that here, this microstructure is initiated by elastic instability and shear anisotropy in the ¡100¿ directions.

Facile Al2O3 coating suppress dissolution of Mn2+ in Mn-substituted Na3V2(PO4)3 with outstanding electrochemical performance for full sodium ion batteries

Na3V2(PO4)3 (NVP) encounters significant obstacles, including limited intrinsic electronic and ionic conductivities, which hinder its potential for commercial feasibility. Currently, the substitution of V3+ with Mn2+ is proposed to introduce favorable carriers, enhancing the electronic conductivity of the NVP system while providing structural support and stabilizing the NASICON framework. This substitution also widens the Na+ migration pathways, accelerating ion transport. Furthermore, to bolster stability, Al2O3 coating is applied to suppress the dissolution of transition metal Mn in the electrolyte. Notably, the Al2O3 coating serves a triple role in reducing HClO4 concentration in the electrolyte, inhibiting Mn dissolution, and functioning as the ion-conducting phase. Likewise, carbon nanotubes (CNTs) effectively hinder the agglomeration of active particles during high-temperature sintering, thereby optimizing the conductivity of NVP system. In addition, the excellent structural stability is investigated by in situ XRD measurement, effectively improving the volume collapse during Na+ de-embedding. Moreover, the Na3V5.92/3Mn0.04(PO4)3/C@CNTs@1wt.%Al2O3 (NVMP@CNTs@1wt.%Al2O3) possesses unique porous structure, promoting rapid Na+ transport and increasing the interface area between the electrolyte and the cathode material. Comprehensively, the NVMP@CNTs@1wt.%Al2O3 sample demonstrates a remarkable reversible specific capacity of 122.6 mAh/g at 0.1 C. Moreover, it maintains a capacity of 115.9 mAh/g at 1 C with a capacity retention of 90.2 mAh/g after 1000 cycles. Even at 30 C, it achieves a capacity of 87.9 mAh/g, with a capacity retention rate of 84.87 % after 6000 cycles. Moreover, the NVMP@CNTs@1wt.%Al2O3//CHC full cell can deliver a high reversible capacity of 205.5 mAh/g at 0.1 C, further indicating the superior application potential in commercial utilization.

Pressure-induced phase transformation and mechanical stability of HfAl2

Utilizing the particle swarm optimization algorithm in conjunction with first-principles calculations, we systematically investigated the structural evolution and mechanical properties of HfAl2 up to 300 GPa at 0 K. Our findings indicate that HfAl2 adopts the MgZn2-type structure (hP12-HfAl2) with space group P63/mmc under zero pressure, and a phase transition to oC12-HfAl2 occurs at approximately 260 GPa. This transition, characterized by a volume collapse, is identified as a first-order phase transition. Phonon dispersion curves provide supporting evidence for the structural stability of these two phases. Simultaneously, we conducted a comprehensive assessment of the elastic constants and modulus of these two phases under both zero and high pressure. The research findings substantially will enhance our understanding of the structural evolution in HfAl2 under high pressure.

Superconductivity in Quasi-One-Dimensional Ferromagnet CrSbSe3 under High Pressure.

Nearly a decade has passed since the discovery of superconductivity in CrAs, but until now, the discovered structure types of chromium-based superconductors are still scanty. It is urgent to expand this family to decipher the interplay between magnetism and superconductivity penetratingly. Here, we report the observation of superconductivity in ferromagnet CrSbSe3 with a quasi-one-dimensional structure under high pressure. Under compression, CrSbSe3 undergoes an insulator-to-metal transition and sequential isostructural phase transitions accompanied by volume collapse. Superconductivity emerges at 32.8 GPa concomitant with metallization in CrSbSe3. A maximum superconducting transition temperature Tc of 7.7 K is achieved at 57.9 GPa benefiting from both the phonon softening and the enhanced p-d hybridization between Se and Cr in CrSbSe3. The discovery of superconductivity in CrSbSe3 expands the existing chromium-based superconductor family and sheds light on the search for concealed superconductivity in low-dimensional van der Waals materials.

Further development of high-amplitude underwater sound sources at The University of Texas Applied Research Laboratories

Following the early research on the Combustive Sound Source (CSS), described in the previous talk, additional development occurred in the 2000’s and beyond, which included work on both the CSS and a new source, the Rupture Induced Underwater Sound Source (RIUSS). Development of the CSS in this era included maximizing the output of the source, investigating the use of CSS in arrays, and towing the source. The CSS was also deployed in surveys conducted during Shallow Water ’06 and the Seabed Characterization Experiment. In part due to lessons learned during those surveys, the RIUSS was conceived and developed. The RIUSS functions by placing a rupture disk over an evacuated chamber and mechanically breaking the disk (either by striking on demand or via hydrostatic pressure) at a specified depth to initiate a volume collapse that produces an impulsive acoustic waveform. The development and use of each sound source will be provided along with high-speed underwater video, examples of signatures, and examples of the efficacy of the sources in ocean acoustics research. [Work Supported by ONR and NAVO].

Indications of flat bands driving the δ to α volume collapse of plutonium

On cooling from the melt, plutonium (Pu) undergoes a series of structural transformations accompanied by a ≈ 28% reduction in volume from its δ phase to its α phase at low temperatures. While Pu's partially filled 5f-electron shells are known to be involved, their precise role in the transformations has remained unclear. By using calorimetry measurements on α-Pu and gallium-stabilized δ-Pu combined with resonant ultrasound and X-ray scattering data to account for the anomalously large softening of the lattice with temperature, we show here that the difference in electronic entropy between the α and δ phases dominates over the difference in phonon entropy. Rather than finding an electronic specific heat characteristic of broad f-electron bands in α-Pu, as might be expected to occur within a Kondo collapsed phase in analogy with cerium, we find it to be indicative of flatter subbands. An important role played by Pu's 5f electrons in the formation of its larger unit cell α phase comprising inequivalent lattice sites and varying bond lengths is therefore suggested.

Trifunctional L-Cysteine Assisted Construction of MoO2/MoS2/C Nanoarchitecture Toward High-Rate Sodium Storage.

The volume collapse and slow kinetics reaction of anode materials are two key issues for sodium ion batteries (SIBs). Herein, an "embryo" strategy is proposed for synthesis of nanorod-embedded MoO2/MoS2/C network nanoarchitecture as anode for SIBs with high-rate performance. Interestingly, L-cysteine which plays triple roles including sulfur source, reductant, and carbon source can be utilized to produce the sulfur vacancy-enriched heterostructure. Specifically, L-cysteine can combine with metastable monoclinic MoO3 nanorods at room temperature to encapsulate the "nutrient" of MoOx analogues (MoO2.5(OH)0.5 and MoO3·0.5H2O) and hydrogen-deficient L-cysteine in the "embryo" precursor affording for subsequent in situ multistep heating treatment. The resultant MoO2/MoS2/C presents a high-rate capability of 875 and 420mAhg-1 at 0.5 and 10Ag-1, respectively, which are much better than the MoS2-based anode materials reported by far. Finite element simulation and analysis results verify that the volume expansion can be reduced to 42.8% from 88.8% when building nanorod-embedded porous network structure. Theoretical calculations reveal that the sulfur vacancies and heterointerface engineering can promote the adsorption and migration of Na+ leading to highly enhanced thermodynamic and kinetic reaction. The work provides an efficient approach to develop advanced electrode materials for energy storage.

Thiourea induced the N/S co-doped carbon skeleton suppressing the dissolution of V to boost superior cyclic stability of Na3V2(PO4)3

Currently, poor conductivity property and volume collapse have severly hindered development of Na3V2(PO4)3. Meanwhile, the dissolution of active V leads to the unstable cyclic performance. Traditional modified methods using carbon-based materials only elevate the electronic conductivity, without considering the interaction between carbon skeleton and Na3V2(PO4)3 grains. In this work, the in-situ modified carbon skeleton by N/S diatomic doped derived from thiourea is successfully synthesized through a facile sol-gel route. Significantly, the synergistic effects of N and S elements can provide more defects and active sites in carbon substrate, stimulating more Na+ to participate the electrochemical process. Moreover, the in-situ N/S co-doping strategy promotes amorphous carbon converting to graphitized carbon, effectively accelerating electronic conductivity. Especially, a coral morphology is formed during sintering process, coming from the pyrolysis effect of thiourea. The porous construction can promote the infiltration of electrolyte, enlarging the contact surface areas between particles and electrolyte. Meanwhile, the generated micropores can relieve the pressure from the shrinkage of crystal to enhance the structural stability. More importantly, due to the introduction of S in carbon substrate, stable C–S–C bonds can be formed between carbon molecular layers to increase the layer distance, benefiting for Na+ migration. Notably, a strong C–S–V bridge bond connection is generated that combines Na3V2(PO4)3 and carbon materials, inhibiting the dissolution of V in electrolyte, resulting in superior cyclic stability. NVP/C@N,S-10 % submits high capacities of 90.5 mAh g−1 and 75.9 mAh g−1 at 60 and 80C, remaining 59.2 mAh g−1 and 57.9 mAh g−1 after 20,000 cycles.

Phase Transformation Under High Pressure Radiates as a Double Couple Deep Earthquake

AbstractDeep‐focus earthquakes (DFEs) originating at the Mantle‐Transition‐Zone (MTZ) (400–700 km) have a Double Couple (DC) radiation pattern similar to crustal earthquakes; however, their mechanism is different and governed by high pressures (15–25 GPa) at nucleation depths. We present a model of nucleation and growth of regions of phase transformation, undergoing a sudden reduction in volume (5%–10%), “volume collapse.” Successive symmetry‐breaking instabilities minimize the energy spent to move the boundary of phase discontinuity and a collapsing volume expands as a flattened pancake‐like self‐similarly expanding Eshelby ellipsoidal inclusion. At the vanishing of the M integral, expressing the balance of flows of energy across the inclusion boundary, at a critical value of the pressure, an arbitrarily small inclusion nucleates and grows at constant potential energy driven by the pressure acting on the change in volume. The inclusion develops shear eigenstrains that decompose into two DC, placing one on the basal plane to radiate without energy losses. The symmetric volume collapse radiates out as an anti‐symmetric DC, and the radiated energy is obtained as the “excess energy,” of the ambient pressure acting on the “volume collapse,” reduced by the energy consumed for the growth of the pancake surfaces, with a “pressure drop” (p0 − pcr) driving the expansion emitting a DC, even under full isotropy. The solution explains some features of the DFEs, (a) the DC radiation, (b) their large energies (the Mw 8.3 Okhotsk earthquake [2013]), (c) the absence of volumetric radiation, and (d) why they can originate in the MTZ, a long‐standing open problem.

Theoretical Investigation of Pressure Dependent Structural and Elastic Properties of MnSi Compound

MnSi is a metallic compound that exhibits a structural phase transition as a function of pressure. At ambient conditions, MnSi has a cubic structure such as NaCl type crystal structure. However, at high pressures, it undergoes a structural phase transition to a CsCl type crystal structure. The pressure-dependent structural phase transition in MnSi has been studied using various experimental and theoretical techniques. In the present work, we have used an efficient inter-ionic potential approach to predict pressure dependent structural phase change and associated volume collapse in MnSi. Therein, the potential includes the long-range Coulomb, van der Waals (vdW) interaction, and the short-range repulsive interaction up to second neighbour ions. It has been demonstrated that the Hafemeister and Flygare approach successfully evaluates the equation of state for change in volume with respect to applied pressure. We have identified a structural phase transition from B1(NaCl) type structure to B2 (CsCl) type structure in this compound. The estimated value of phase transition pressure (Pt) is 42 GPa, which is consistent with the available reported data. The identified first order phase transformation showed a volume collapse of about 10% in the vicinity of transition. In addition, we have also investigated second order of elastic constants for MnSi compound.