Severe local lattice distortions (LLDs), originating from the size mismatch among atoms, have been proposed as one of the key mechanisms responsible for the excellent mechanical properties of bcc-structured high-entropy alloys (HEAs). They have also been connected to phase stability, as well as physical properties such as electrical conductivity. Experimental measurements of LLDs are, however, difficult and often ambiguous. Analysis of total scattering data in real space has been proposed to provide a uniquely suitable probe of LLDs, but its widespread application and validation are still limited. We conduct a thorough study of LLD measurements in refractory high-entropy alloys (RHEAs) using small-box pair distribution function (PDF) analysis. We start by reexamining existing literature data using a recently proposed coherent theoretical framework to demonstrate that LLDs in RHEAs can indeed be considered as severe and can be reliably measured even in the absence of known thermal components. We perform total scattering experiments of a typical RHEA (HfNbTaTiZr) using both x-rays and neutrons, and show that real-space PDF analysis of data from different types of radiation gives consistent values of LLDs. The results are also in good agreement with the values derived from reciprocal-space data. Finally, through simulation and analysis of theoretical two-phase PDFs, we demonstrate that the effect of the chemical segregation in the investigated RHEA on the measured LLDs is limited when dealing with comparatively large LLDs. The results show that PDF analysis using small-box modeling provides a fast and reliable tool for measuring LLDs in RHEAs, which makes it ideal for analysis of large data sets from time-resolved in situ measurements.

Two-dimensional (2D) elemental ferroelectricity has recently been confirmed and arouses great interest in exploring new elemental asymmetric structures and their symmetry-breaking related properties. In this study, our density functional theory (DFT) calculations reveal the existence of coupled in-plane and out-of-plane electric polarizations in the group $\mathrm{V}$ elements $\alpha \text{−}X6$ ($\mathit{X}=\mathrm{P}$, As). These ferroelectric phases are stabilized through charge transfer between $p_{\mathrm{x}}$ orbitals. The introduction of compressive strain facilitates the transformation from blue phosphorene into $\alpha$-P6 phase with low reaction energy owing to their structural similarity. In addition, strain engineering or atom substitution can effectively reduce the polarization switching barrier. Furthermore, $\alpha \text{−}X6$ structure exhibits large longitudinal piezoelectric strain coefficients $d_{11}$, benefiting from their moderate $e_{11}$ and flexible character. This discovery not only enriches the family of elemental ferroelectrics but also deepens the understanding of the origin of elemental polarization, offering potential candidates for ferroelectric and piezoelectric applications.

Evolution of nanocrystalline (NC) tungsten under radiation exposure is investigated by atomic scale simulations in the low temperature high dose limit. Statistical analysis of samples containing at least a million atoms, with grain size varying from 5 nm to 20 nm, shows that the pattern of microstructural evolution of a NC material differs significantly from that of a single crystal. The high resistance to swelling in the low grain size limit stems from a combined effect of the initial excess volume of atomic configurations at grain boundaries and high integral volume of grain boundary defect-denuded zones. Grain boundaries annihilate defects through the rearrangement of their local atomic configurations acting as fluctuating dynamic sinks for defects. Grain size distribution slowly broadens as a function of dose, delaying the onset of an asymptotic radiation-driven steady state in comparison with a single crystalline material. Spatial limitations imposed by the size and topology of grains prevent the formation of a percolating dislocation network, resulting in only isolated dislocation loops being retained in the microstructure even at high radiation exposure.

${\mathrm{Nb}}_3\mathrm{Sn}$ conductors are important candidates for high-field magnets for particle accelerators, and they continue to be widely used for many laboratory and nuclear magnetic resonance magnets. However, the critical current density, $J_c$, of present ${\mathrm{Nb}}_3\mathrm{Sn}$ conductors declines swiftly above 12–15 T. State-of-the-art Ta- and Ti-doped strands exhibit upper critical field, $H_{c2}$, values of ∼24–26.5 T (4.2 K) and do not reach the Future Circular Collider target $J_c$, which serves as the present stretch target for ${\mathrm{Nb}}_3\mathrm{Sn}$ development. As recently demonstrated, to meet this goal requires enhanced vortex pinning but an independent and supplementary approach is to significantly enhance $H_{c2}$. In this study, we have arc melted multiple Nb alloys with added Hf, Zr, Ta, and Ti and drawn them successfully into monofilament wires to investigate the possibilities of $H_{c2}$ enhancement through alloying. $H_{c2}\left(T\right)$ was measured for all samples in fields up to 16 T and some up to 31 T. We have found that all alloys show good agreement with the standard Werthamer, Helfand, and Hohenberg fitting procedure without the need to adjust the paramagnetic limitation parameter (α) and spin-orbit scattering parameter $\left({\lambda }_{\mathrm{so}}\right)$. The evaluation of $d{H}_{c2}/dT$ near $T_c$, which is proportional to the electronic specific heat coefficient γ and the normal state resistivity ${\rho }_{\mathrm{n}}$, allows a better understanding of the induced disorder introduced by alloying in the A15 phase. So far, we have observed that Hf alloying of pure Nb can enhance $H_{c2}\left(0\right)$ by 3–4 T to ∼28 T, while adding just $1\text{at.}\%$ Hf or Zr into a Nb-4 at. % Ta base alloy can raise $H_{c2}\left(0\right)$ to ∼31 T. Very importantly we find that Hf and Zr raise the alloy recrystallization temperature above the usual A15 reaction temperature range of $650{}^{\circ }\mathrm{C}-750{}^{\circ }\mathrm{C}$, thus ensuring denser A15 phase nucleation in the Nb alloy grain boundaries, possibly leading to a more homogeneous A15 phase Sn content and refined A15 grain size. The potential for further advancements in ${\mathrm{Nb}}_3\mathrm{Sn}$ properties is explored in relation to the recrystallization of the Nb alloy and the factors controlling the upper critical field.

Two-dimensional (2D) materials have attracted vast research interest since the breakthrough discovery of graphene. One major benefit of such systems is the ability to tune the Fermi level through the charge neutrality point between electron and hole doping. Here we show that single layer graphene coupled to the low-density superconductor indium oxide (InO) exhibits two charge neutrality points, each of them representing electronic regions in which the carrier density can be tuned from hole to electron dominated. This is not seen in clean graphene or in a bilayer where the carrier density is extremely low. We suggest that the second charge neutrality point results from regions in the graphene layer just below superconducting islands in InO, where pairing is induced via the proximity effect; gating of this hybrid system therefore allows the tuning from hole to electron superconductivity through an ultralow carrier density regime. We propose this as a “superconducting Dirac point (SDP)” where intravalley scattering is greatly enhanced. Our results suggest that the electronic states around SDP behave like those in a strongly coupled superconductor.

We explore the effect of thickness, magnetization direction, strain, and gating on the topological quantum phase transition of a thin-film magnetic topological insulator. Reducing the film thickness to the ultrathin regime couples the edge states on the two surfaces, opening a gap known as the hybridization gap, and causing a phase transition from a topological insulator to a normal insulator (NI). An out-of-plane/in-plane magnetization of size proportional to the hybridization gap triggers a phase transition from a normal insulator state to a quantum anomalous Hall (QAH)/semimetal state. A magnetization tilt by angle $\theta$ from the out-of-plane axis influences the topological phase transition in a way that for sufficiently large $\theta$, no phase transition from NI to QAH can be observed regardless of the sample thickness or magnetization, and for $\theta$ close to $\pi /2$ the system transits to a semimetal phase. Furthermore, we demonstrate that compressive/tensile strain can be used to decrease/increase the magnetization threshold for the topological phase transition. Finally, we reveal the effect of a vertical potential acting on the film, be it due to the substrate or applied gating, which breaks inversion symmetry and raises the magnetization threshold for the transition from NI to QAH state.

The Bi-Ni binary system has been of interest due to possible unconventional superconductivity aroused therein, such as time-reversal symmetry breaking in Bi/Ni bilayers or the coexistence of superconductivity and ferromagnetism in ${\mathrm{Bi}}_3\mathrm{Ni}$ crystals. While Ni acts as a ferromagnetic element in such systems, the role of the strong spin-orbit coupling element Bi in superconductivity has remained unexplored. In this work, we systematically studied the effects of Bi stoichiometry on the superconductivity of ${\mathrm{Bi}}_x{\mathrm{Ni}}_{1–x}$ thin films ($x\approx 0.5–0.9$) fabricated via a composition-spread approach. The superconducting phase map of ${\mathrm{Bi}}_x{\mathrm{Ni}}_{1–x}$ thin films exhibited a superconducting composition region attributable to the intermetallic ${\mathrm{Bi}}_3\mathrm{Ni}$ phase with different amounts of excess Bi, revealed by synchrotron x-ray diffraction analysis. Interestingly, the mixed-phase region with ${\mathrm{Bi}}_3\mathrm{Ni}$ and Bi showed unusual increases in the superconducting transition temperature and residual resistance ratio as more Bi impurities were included, with the maximum $T_{\mathrm{c}}$ ($=4.2\mathrm{K}$) observed at $x\approx 0.79$. A correlation analysis of structural, electrical, and magneto-transport characteristics across the composition variation revealed that the unusual superconducting “dome” is due to two competing roles of Bi: impurity scattering and carrier doping. We found that the carrier doping effect is dominant in the mild doping regime $(0.74\le x\le 0.79)$, while impurity scattering becomes more pronounced at larger Bi stoichiometry.

An appealing direction to change the properties of strongly correlated materials is to induce nonequilibrium steady states by the application of a direct current. While access to these novel states is of high scientific interest, Joule heating due to current flow often constitutes a hurdle to identify nonthermal effects. The biggest challenge usually resides in measuring accurately the temperature of a sample subjected to direct current, and to use probes that give direct information of the material. In this work, we exploit the simultaneous measurement of electrical transport and magnetization to probe nonequilibrium steady states in ${\mathrm{Ca}}_2\mathrm{Ru}{\mathrm{O}}_4$. In order to reveal nonthermal current-induced effects, we employ a simple model of Joule self-heating to remove the effects of heating and discuss the importance of temperature inhomogeneity within the sample. Our approach provides a solid basis for investigating current-induced phenomena in highly resistive materials.

Ternary nitride ${\mathrm{MgSnN}}_2$ is a promising candidate to fill the “green gap” of nitride-based light-emitting diodes. The coexistence of two different valence cations offers a unique tunability on its electronic properties through controlling the degree of cation site ordering without a concomitant change in stoichiometry. In this work, the structural and electronic properties of cation-disordered ${\mathrm{MgSnN}}_2$ are studied through a combination of density functional theory calculations, cluster expansion, and Monte Carlo simulations. The order-disorder phase transition is analyzed, and the short-range and long-range order parameters quantifying the degree of disorder are calculated. A strong correlation between the two parameters is observed, indicating the absence of the octet-rule-conserving disorder. Cation disorder has two main effects on the electronic properties of ${\mathrm{MgSnN}}_2$. One is the reduction of the band gap, and the other is the strong localization of valence band edge states. Further analysis showed that the localization is a consequence of the weak interatomic coupling between the N atoms and the disorder-induced fluctuation of the local electrostatic potentials on the N atoms. These results could be helpful for the understanding of disorder effects in ${\mathrm{MgSnN}}_2$, as well as the tuning of its properties through the control of cation ordering.

In this study, we present an effective tight-binding model for an accurate description of the lowest energy quadruplet of a conduction band in a ferromagnetic $\mathrm{Cr}{X}_3$ monolayer, tuned to the complementary ab initio density functional theory simulations. This model, based on a minimum number of chromium orbitals, captures a distinctively flat dispersion in those bands but requires taking into account hoppings beyond nearest neighbors, revealing ligand-mediated electron pathways connecting remote chromium sites. Doping of states in the lowest conduction band of $\mathrm{Cr}{X}_3$ requires charge transfer, which, according to recent studies [Tenasini et al., Nano Lett. 22, 6760 (2022); Tseng et al., Nano Lett. 22, 8495 (2022); Cardoso et al., Phys. Rev. B 108, 184423 (2023)], can occur in $\mathrm{graphene}\left(\mathrm{G}\right)/\mathrm{Cr}{X}_3$ heterostructures. Here, we use the detailed description of the lowest conduction band in ${\mathrm{CrI}}_3$ to show that $\mathrm{G}/{\mathrm{CrI}}_3/\mathrm{G}$ and $\mathrm{G}/{\mathrm{CrI}}_3$ are type-II heterostructures where light holes in graphene would coexist with heavy electrons in the magnetic layer, where the latter can be characterized by Wigner-Seitz radius $r_s\sim 25-35$ (as estimated for hBN-encapsulated structures).

Topological insulator–magnetic insulator (TI–MI) heterostructures hold significant promise in the field of spintronics, offering the potential for manipulating magnetization through topological surface state–enabled spin-orbit torque. However, many TI–MI interfaces are plagued by issues such as contamination within the magnetic insulator layer and the presence of a low-density transitional region of the topological insulator. These interfacial challenges often obscure the intrinsic behavior of the TI–MI system. In this study, we addressed these challenges by depositing sputtered ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ on liquid phase epitaxy grown ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}/{\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$. The liquid phase epitaxy grown ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ has been previously shown to have exceptional interface quality, without an extended transient layer derived from interdiffusion processes of the substrate or impurity ions, thereby eliminating rare-earth impurity-related losses in the MI at low temperatures. At the TI–MI interface, high-resolution depth-sensitive polarized neutron reflectometry confirmed the absence of a low-density transitional growth region of the TI. By overcoming these undesirable interfacial effects, we isolate and probe the intrinsic low-temperature magnetization dynamics and transport properties of the TI–MI interface. Our findings revealed strong spin pumping at low temperatures, accompanied by an additional in-plane anisotropy. The enhanced spin pumping at low temperatures is correlated with the observed suppression of bulk conduction and the weak antilocalization in the TI film, highlighting the interplay between the transport and spin pumping behavior in the TI–MI system.

The spin-$1/2$ ferromagnetic XXZ chain is a prototypical many-body quantum model, exactly solvable via the integrable Bethe ansatz method, hosting a Tomonaga-Luttinger spin liquid. However, its clear experimental realizations remain absent. Here, we present a thorough investigation of the magnetism of the structurally disorder-free compound $\mathrm{LuCu}{\left(\mathrm{OH}\right)}_3{\mathrm{SO}}_4$. By conducting magnetization and electron-spin-resonance measurements on the single-crystal sample, we establish that the title compound approximates the spin-$1/2$ ferromagnetic XXZ chain model with a nearest-neighbor exchange strength of $J_1\sim 65\mathrm{K}$ and an easy-plane anisotropy of $\sim 0.994$. The specific heat demonstrates a distinctive power-law behavior at low magnetic fields (with energy scales $\le 0.02J_1$) and low temperatures $(T\le 0.03J_1)$. This behavior is consistent with the expectations of the ideal spin-$1/2$ ferromagnetic XXZ chain model, thereby supporting the formation of a gapless Tomonaga-Luttinger spin liquid in $\mathrm{LuCu}{\left(\mathrm{OH}\right)}_3{\mathrm{SO}}_4$.

Giant magnetic transverse thermoelectric effect, anomalous Nernst effect (ANE), was theoretically and experimentally observed in $3d$-transition metal compounds. The intrinsic components of ANE can be described from the electronic structure based on the Berry phase concept. The topological electronic structure, such as the Weyl node and nodal lines, induces large Berry curvature, one origin of giant ANE. We investigated transverse thermoelectric properties on ferromagnetic $\mathrm{D}{0}_3$-type Heusler compounds ${\mathrm{Fe}}_3\mathrm{Si}$ based on first-principles calculations. We found large transverse thermoelectric conductivity ${\alpha }_{xy}\sim 5{\mathrm{AK}}^{-1}{\mathrm{m}}^{-1}$ is realized with hole carrier doping at room temperature. We also clarified that the nodal line and its stationary point enhance transverse thermoelectric conductivity. These results give us a clue to design high-performance ANE-based magnetic thermoelectric materials.

While the process by which a polymer crystal nucleates from the melt has been extensively studied via molecular simulation, differences in polymer models and simulated crystallization conditions have led to seemingly contradictory results. We make steps to resolve this controversy by computing low-temperature phase diagrams of oligomer melts using Wang-Landau Monte Carlo simulations. Two qualitatively different crystallization mechanisms are possible depending on the local bending stiffness potential. Polymers with a discrete bending potential crystallize via a single-step mechanism, whereas polymers with a continuous bending potential can crystallize via a two-step mechanism that includes an intermediate nematic phase. Other model differences can be quantitatively accounted for using an effective volume fraction and a temperature scaled by the bending stiffness. These results suggest that at least two universality classes of nucleation exist for melts and that local chain stiffness is a key determining factor in the mechanism of nucleation.

Currently, the dominant model for the formation of enhanced magnetostriction of Fe-Ga alloys is based on the assumption of the presence of microscopic inclusions with a tetragonal $L{6}_0$ structure in the cubic matrix of the alloy. However, no evidence for the presence of this phase in the bulk of the alloys in amounts sufficient to have a noticeable effect on the magnitude of magnetostriction has been obtained so far. To test this hypothesis, a detailed scanning of the reciprocal space of $\mathrm{F}{\mathrm{e}}_{81}\mathrm{G}{\mathrm{a}}_{19}\mathrm{T}{\mathrm{b}}_{0.1}$ and ${\mathrm{Fe}}_{73}{\mathrm{Ga}}_{27}$ single crystals was carried out at ESRF at high photon flux stations. In particular, it was possible to reliably record superstructure diffraction peaks, the intensity of which was at a level of $2\times {10}^{-6}$ from the intensity of the fundamental peaks. Nevertheless, neither the presence of superstructure diffraction peaks obviously belonging to the $L{6}_0$ phase nor the tetragonal splitting of the fundamental diffraction peaks into components, which could indicate the presence of this phase in the samples, was detected. Similar results were obtained using complementary methods (electron and neutron diffraction). Based on the performed analysis of the background level in the places of the expected positions of superstructure peaks of the $L{6}_0$ phase, it was found that the volume fraction of this phase in the $\mathrm{F}{\mathrm{e}}_{81}\mathrm{G}{\mathrm{a}}_{19}\mathrm{T}{\mathrm{b}}_{0.1}$ alloy cannot exceed 0.2 %. The presence of a previously discovered $X$ phase with hexagonal or orthorhombic symmetry in a crystal with 27 at. % Ga was confirmed.

With strong correlations between lattice, spin, and charge degrees of freedom, the layered ruthenate $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$ has attracted considerable interest over the past few decades due to its metal-insulator transition, antiferromagnetic-to-ferromagnetic transition, metamagnetic transition, and orbital ordering. Much effort has been devoted to manipulating its crystalline structure through epitaxial strain, chemical substitution, and pressure to clarify the underlying many-body physics and related quantum critical phenomena. Here we report a comprehensive proton intercalation study of $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$ thin films and investigate their magneto-transport properties arising from structural deformations and carrier doping. It reveals a rich phase diagram with distinct electronic and magnetic ground states. Specifically, with increasing gate voltage during ionic liquid gating, the film first evolves from an insulating state into a metallic state and then gradually turns towards an exotic Mott insulator. Furthermore, we observed an emergent metamagnetic transition from a canted antiferromagnetic to a nearly ferromagnetic state, a characteristic feature conventionally triggered by external magnetic field, but here with electron doping. Our first-principles calculations reveal that these unexpected features could be attributed to the proton evolution-induced synergistic structural distortion and electron doping during ionic liquid gating. Our findings highlight the important role of both lattice and charge degrees of freedom in the intriguing electronic states of $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$ and provide an effective approach to uncover different properties in quantum materials.

We report a comprehensive set of polarized Raman spectra on thin-film multilayers of the high-$T_c$ superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ and electrically insulating manganites $R{\mathrm{MnO}}_3$ ($R=$ rare-earth partially substituted with group-II elements) hosting magnetic, charge and orbital order (COO). Such multilayers have been shown to exhibit a unique insulating-to-superconducting transition that is induced by magnetic field, electric field, or by tailoring the chemical composition of the $R$ site of the manganite. The Raman spectra show significant Jahn-Teller distortions of the manganite structure, which correlate with COO, approximately 90 K above the magnetic ordering temperature of 140 K. Based on the Raman data and earlier electrical transport studies of single-layer manganite films, we argue that the manganite layers in our heterostructures remain electrically insulating across the range of investigated temperatures, dopings, and magnetic fields. The Raman spectra show a pronounced redshift and broadening of lattice vibrations around 200 ${\mathrm{cm}}^{-1}$ in the multilayers compared to those of manganite films, which may indicate hybridization with ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ phonons. We also observe additional excitations at 690 ${\mathrm{cm}}^{-1}$ and 830 ${\mathrm{cm}}^{-1}$ that are absent in the single films or bulk responses, which we discuss to originate from the cuprate/manganite interface. These observations demonstrate that the phonon spectrum is significantly modified in our multilayer samples. This is expected to play an important role in the mechanism of the insulating-to-superconducting transition found in these cuprate-manganite multilayers.

The use of machine learning algorithms is exponentially growing and concerns are being raised about their sustainability. Neuromorphic computing aims to mimic the architecture and the information processing mechanisms of the mammalian brain, appearing as the only avenue that offers significant energy savings compared to the standard digital computers. Memcapacitive devices, which can change their capacitance between different nonvolatile states upon the application of electrical stimulation, can significantly reduce the energy consumption of bio-inspired circuitry. In the present work, we study the multi-mem (memristive and memcapacitive) behavior of devices based on thin films of the topotactic redox $\mathrm{L}{\mathrm{a}}_{1/2}\mathrm{S}{\mathrm{r}}_{1/2}\mathrm{M}{\mathrm{n}}_{1/2}\mathrm{C}{\mathrm{o}}_{1/2}{\mathrm{O}}_{3-x}$ (LSMCO) perovskite modified with Sm:$\mathrm{Ce}{\mathrm{O}}_2$ (SCO), grown on Nb:${\mathrm{SrTiO}}_3$ with (001) and (110) out-of-plane orientations. Either the self-assembling at the nanoscale of both LSMCO and SCO phases or the doping with Ce(Sm) of the LSMCO perovskite were observed for different fabrication conditions and out-of-plane orientations. The impact of these changes on the device electrical behavior was determined. The optimum devices resulted those with (110) orientation and Ce(Sm) doping the perovskite. These devices displayed a multi-mem behavior with robust memcapacitance and significantly lower operation voltages (especially the reset voltage) in comparison with devices based on pristine LSMCO. In addition, they were able to endure electrical cycling—and the concomitant perovskite topotactic redox transition between oxidized and reduced phases—without suffering nanostructural changes nor cationic segregation. We link these properties to an enhanced perovskite reducibility upon Ce(Sm) doping. Our work contributes to increasing the reliability of LSMCO-based multi-mem systems and to reducing their operating voltages closer to the 1 V threshold, which are key issues for the development of nanodevices for neuromorphic or in-memory computing.

Having a strong electromagnetic absorption, MXene multilayers are readily envisaged for applications in electromagnetic shields and related prospective technology. However, an $\mathit{ab}$ initio characterization of the optical properties of MXenes is still lacking, due in part to major difficulties with the treatment of metallicity in the first-principles approaches. Here we addressed the latter challenge, after a careful treatment of intraband transitions, to present a thorough analysis of the electronic and optical properties of a selected set of metallic MXene layers based on density functional theory (DFT) and many-body perturbation theory calculations. Our results reveal that the $\mathit{GW}$ corrections are particularly important in regions of the band structure where $\mathit{d}$ and $\mathit{p}$ states hybridize. For some systems, we show that $\mathit{GW}$ corrections open a gap between occupied states, resulting in a band structure that closely resembles that of an intrinsic transparent conductor, thereby opening an additional line of prospective applications for the MXenes family. Nevertheless, $\mathit{GW}$ and Bethe-Salpeter corrections have a minimal influence on the absorption spectra, in contrast to what is typically observed in semiconductor layers. Our present results suggest that calculations within the independent particle approximation (IPA) calculations are sufficiently accurate for assessing the optical characteristics of bulk-layered MXene materials. Finally, our calculated dielectric properties and absorption spectra, in agreement with existing experimental data, confirm the potential of MXenes as effective infrared emitters.

The local atomic structure of NaF-$\mathrm{Zr}{\mathrm{F}}_4$ (53–47 mol%) molten system and its evolution with temperature are examined with x-ray scattering measurements which are then used to validate the quality of ab initio and neural network-based molecular dynamics (NNMD) calculations in the temperature range $515-700{}^{\circ }\mathrm{C}$. The machine-learning enhanced NNMD calculations offer improved efficiency while maintaining accuracy at higher distances compared to ab initio calculations. Looking at the evolution of the pair distribution function with increasing temperature, a fundamental change in the liquid structure within the selected temperature range, accompanied by a slight decrease in overall correlation is revealed. NNMD calculations indicate the coexistence of three different fluorozirconate complexes: ${\left[\mathrm{Zr}{\mathrm{F}}_6\right]}^{2-}, {\left[\mathrm{Zr}{\mathrm{F}}_7\right]}^{3-}$, and ${\left[\mathrm{Zr}{\mathrm{F}}_8\right]}^{4-}$, with a shift in the dominant coordination state from the 7-coordinated Zr cation toward a 6-coordinated cation with increasing temperature. The study also highlights the metastability of different local coordination structures, with frequent interconversions between the 6- and 7-coordinate states. Analysis of the Zr-F-Zr angular distribution function reveals the presence of both “edge-sharing” and “corner-sharing” fluorozirconate complexes with specific bond angles and distances in accord with previous studies, while the next-nearest-neighbor cation-cation correlations demonstrate a clear preference for unlike cations as nearest-neighbor pairs, emphasizing nonrandom arrangement. These findings contribute to a comprehensive understanding of the complex local structure of the molten salt, providing insights into temperature-dependent preferences and correlations within the molten system.