We investigate how chirality influences the excitonic response to pressure in chiral versus racemic (Cl-methylbenzylammonium)2PbI4. Above 4 GPa, we observe a reduction of the exciton redshift rate in the chiral samples compared to the racemate, a behavior paralleling the evolution of the N-H vibrational modes in the infrared spectrum. We hypothesize that, at 4 GPa, the asymmetric N-H & ctdot;I bonding network in the chiral systems reaches the limit of its buffering capability. Further compression is then accommodated through octahedral distortion, enhancing the chiral character of the inorganic sublattice. The corresponding modification of the octahedral angles reduces Pb-s/I-p orbital coupling, explaining the decrease in the exciton redshift rate. Conversely, the symmetric N-H & ctdot;I bonds in the racemate prove more effective at accommodating compression without altering the octahedral orientation. Our results demonstrate that chirality governs the tunability of both organic-inorganic interactions and the excitonic response under external stimuli in two-dimensional perovskites.

Bulk modulus is a fundamental property of matter that links volume reduction to compression. Despite its significance for practical applications, this parameter is rarely documented in the literature on chemically complex alloys. In this work, experimental assessment of bulk modulus in the series of bcc alloys TiVNb, (TiVNb)90Al10, (TiVNb)90Mo10, (TiVNb)90Al5Mo5 and (TiVNb)80Al10Mo10 is reported by in situ synchrotron X-ray diffraction (XRD) using a diamond anvil cell. Theoretical estimations based on the empirical rule of mixture (ROM) and density functional theory (DFT) modelling are also provided and compared to experimental findings. These values are in excellent agreement for TiVNb but diverge for alloys with larger elemental diversity (quaternary and quinary compositions). Experiments demonstrated that the addition of 10at.% Al or Mo into TiVNb decreases the bulk modulus, while from ROM and DFT estimations only Al exhibits this behavior. These alloys have previously shown promising hydrogen storage properties. An attempt was therefore made to establish a correlation between the bulk modulus and the enthalpy of hydride formation. We conclude that further experimental studies are required to fully understand the impact of elastic properties on the design of chemically complex alloys for solid-state hydrogen energy storage.

La_3Ni_2O_7, a bilayer nickelate with Ruddlesden-Popper structure, undergoes a pressure-induced structural transition from a tilted Amam phase to an untilted Fmmm (or I4/mmm) phase near 10-15 GPa, concomitant with the emergence of high-T_c superconductivity (T_c ∼ 80 K). Despite intense interest, the phase boundaries and the impact of structural changes on the electronic properties remain unclear. Here, we combine high-pressure and high-temperature Raman and synchrotron-based infrared spectroscopies to map the structural and electronic evolutions. Raman measurements confirm the pressure-driven structural transition and reveal the emergence of Fano line shapes, indicating enhanced electron-phonon coupling. High-temperature data show analogous spectral signatures above 544 K, suggesting an unreported upper temperature limit of the Amam phase within the T-P phase diagram of this system. Infrared reflectivity measurements evidence a concomitant metallization, with a tremendous two-order-of-magnitude increase in carrier density, marking a crossover from a bad metal to a good metal. These results establish a unified picture of the structural transition and its strong coupling to the electronic properties.

The interplay between electronic correlations, density wave orders, and magnetism gives rise to several fascinating phenomena. In recent years, kagome metals have emerged as an excellent platform for investigating these unique properties, which stem from their itinerant carriers arranged in a kagome lattice. Here, we show that electronic structure of the prototypical kagome metal, Fe$_3$Sn$_2$, can be tailored by manipulating the breathing distortion of its kagome lattice with external pressure. The breathing distortion is suppressed around 15 GPa and reversed at higher pressures. These changes lead to a series of Lifshitz transitions that we detect using broadband and transient optical spectroscopy. Remarkably, the strength of the electronic correlations and the tendency to carrier localization are enhanced as the kagome network becomes more regular, suggesting that breathing distortion can be a unique control parameter for the microscopic regime of the kagome metals and their electron dynamics.

Y-kapellasite [Y_{3}Cu_{9}(OH)_{19}Cl_{8}], which hosts an original anisotropic kagome sublattice, is a promising candidate for studying elusive and complex correlated physics. It exhibits a theoretically predicted in-plane (1/3,1/3) magnetic order [Hering et al., npj Comput. Mater. 8, 1 (2022)2057-396010.1038/s41524-021-00689-0], but its magnetic interaction values place it close to a phase boundary to a spin liquid state [Chatterjee et al., Phys. Rev. B 107, 125156 (2023)PRBMDO2469-995010.1103/PhysRevB.107.125156]. Our μSR measurements under hydrostatic pressure demonstrate the complete suppression of static magnetism in favor of a fully dynamical ground state at 2.3 GPa. Complementary high-pressure x-ray and optical phonon measurements reveal a gradual reduction of the kagome anisotropy, enhancing magnetic frustration without structural transitions. Our results establish Y-kapellasite as a rare clean kagome model in which long-range order is suppressed by pressure-tuned frustration, the first fingerprint for the realization of a quantum spin liquid without strong disorder.

Mercury telluride (HgTe) nanocrystals are cornerstone materials for infrared optoelectronics, yet all previously reported forms of HgTe have crystallized in the zinc blende phase. Here, we develop a comprehensive cation exchange route to access metastable wurtzite (WZ) HgTe in both spherical and nanorod morphologies. Structural and spectroscopic characterizations show that WZ HgTe NCs retain the strong confinement tunability of their optical properties while introducing non-cubic lattice and distinct electronic topology. Ab initio modeling reveals that bulk WZ HgTe is a Dirac semimetal, whereas quantum confinement opens a direct gap that enables bright short-wave infrared emission. High-pressure studies demonstrate an irreversible WZ-to-zinc blende phase transition, consistent with its metastable nature, while the WZ phase remains stable at cryogenic temperatures. Electrically driven light-emitting diodes based on WZ HgTe nanorods exhibit superior electroluminescence beyond 2 μm, establishing a platform bridging topological semimetals and confined infrared emitters.

Controlling the crystal phase of two-dimensional transition metal dichalcogenides (TMDs) is essential for tailoring their electronic and optical properties. Among the polymorphs of WS2, the metastable 1T' phase exhibits semimetallic or narrow-bandgap character and hosts quantum functionalities distinct from the semiconducting 1H phase. Here, we investigate the temperature-induced 1T'/1H phase transition in colloidally synthesized monolayer WS2 nanosheets functionalized with organic ligands. The reducing conditions of the synthesis stabilize the 1T' phase via electron doping. Through in situ analyses of both the structural and electronic properties, we monitor the phase evolution during annealing and find that the 1T' phase remains stable up to 300 °C, accompanied by a relative lattice contraction. Between 300 °C and 350 °C, a mixed 1T'/1H regime appears, where the 1H content can be finely tuned by controlling the annealing time. Above 350 °C, a rapid and complete transformation to the 1H phase occurs. We demonstrate that the decomposition of the reducing ligand serves as the primary trigger of the structural transition, revealing a strong interplay among doping, surface chemistry, and lattice structure. Notably, nanosheets with smaller lateral dimensions exhibit slower phase transition kinetics, suggesting that finite size could influence the structural rearrangement underlying the phase transformation.

The pressure dependence of structural behavior in the orthorhombic (Pccn, PI) and monoclinic (P21/c, PII) polymorphs of the compound [Fe(PM-BiA)2(NCS)2], where PM-BiA = (N-(2'-pyridylmethylene)-4-amino-bi-pheynyl), is studied with synchrotron single-crystal X-ray diffraction and vibrational spectroscopy. Both polymorphs are stable up to ∼1.5 GPa, with a spin state transition occurring only in polymorph PII under hydrostatic conditions as documented by single-crystal synchrotron diffraction. The diffraction data also provide evidence of the formation of superstructures for both PI, with a doubled c axis, and PII, with a doubled b axis, on applying pressures above 2 GPa. The LS and HS states seem to coexist at high-pressures for both polymorphs studied with synchrotron infrared spectroscopy at quasi-hydrostatic conditions. Such results indicate that the occurrence of spin-crossover transformations in [Fe(PM-BiA)2(NCS)2] might strongly depend on the stress in the sample.

In situ study of colloidal WS 2 monolayers shows reducing-ligand stabilization of 1T′ up to 300 °C. At higher temperature, transition to 1H occurs with kinetics controlled by nanosheet size and surface chemistry.

This work presents an in-depth chemical and morphological investigation of the solid electrolyte interphase (SEI) formed on binder-free silicon electrodes, which include both nanowire (Si-NW) and amorphous (a-Si) configurations, for next-generation lithium-ion battery systems. The study focuses on the first five galvanostatic cycles to capture the critical early-stage SEI consolidation process, essential for understanding the interfacial phenomena that dictate long-term performance. By employing innovative electrode fabrication techniques such as plasma-enhanced chemical vapor deposition and utilizing ionic liquid (IL)-based electrolytes-specifically 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) formulations known for their low viscosity and high conductivity-this work addresses the challenges posed by the significant volume changes inherent to Si-based materials. Advanced characterization methodologies, notably Optical-Photothermal Infrared Spectroscopy (O-PTIR) and Raman spectroscopy are utilized to probe the chemical and structural evolution of the SEI with high spatial resolution. This multifaceted approach reveals the interplay between electrode morphology and electrolyte composition on SEI formation and provides valuable insights into the fundamental processes governing irreversible capacity losses and electrode degradation. The findings demonstrate clear material- and electrolyte-dependent differences in SEI characteristics, thereby establishing new avenues for optimizing interfacial stability and battery performance. Overall, the study contributes innovative perspectives on early SEI formation mechanisms critical for the design of safer and more durable high-capacity battery electrodes.

SO2 is a molecule of significant industrial and geochemical importance, known for its role in sulphuric acid production and its natural occurrence in volcanic processes. Recent studies have revealed pressure-induced amorphisation and the formation of polymeric amorphous phases in SO2, behaviours analogous to those observed in other fundamental molecular systems such as CO2, N2, and CS2. Here, we identify a mixture of polymeric SO2 phases, with space groups Ama2 (Z = 2) and Pmc21 (Z = 8), the latter a homologue of γ-SeO2, as the crystalline parents of the previously reported threefold-coordinated amorphous SO2 observed above 25 GPa. These phases were characterized using a combination of advanced synthesis and refined high-pressure loading techniques, alongside x-ray diffraction, Raman, and infrared spectroscopy. Structural assignments were further supported by numerical predictions of candidate crystal structures. Notably, the Ama2 and γ-SeO2-like phases exhibit in the pressure region 20–60 GPa the lowest and near-degenerate enthalpies, Ama2 being stable below 25 GPa and γ-SeO2-like above 25 GPa. Both phases feature distinctive W-shaped polymeric units, a structural motif identified long ago at ambient pressure in the rare-mineral Downeyite (SeO2), but the stacking of chains is different and pressure-dependent. Although SO2 has been shown to form polymeric phases under pressure, characterizing its polymeric forms has remained challenging due to its propensity to amorphize, which leads to spectral signal degradation. Here, the authors identify and characterize Ama2 and γ-SeO2-like SO2 crystalline polymeric phases featuring W-shaped units through a combination of refined high-pressure loading techniques, X-ray diffraction, Raman, and infrared spectroscopy.

Nitrogen, known for its rich polymorphism and kinetic barriers, has served as a valuable testbed for evaluating advanced computational methods. In this study, we investigate the infrared absorptions of gamma -N2, a crystalline molecular configuration that is only accessible via a low-temperature compression, employing synchrotron radiation. Our results reveal that gamma -N2 possesses a simple infrared spectrum consisting of only three far-infrared phononic absorptions: a prominent asymmetric peak made up of two unresolved modes, and a weak higherfrequency peak, all of which could be tracked up to 93 GPa. Critically, no absorption associated with an internal vibrational mode of the N2 molecule was detected up to the highest pressures. Density functional theory (DFT) simulations conducted at 40 GPa demonstrate that these observations align with the P21/c structural model, reinforcing its compatibility as a candidate complimenting existing Raman and x-ray diffraction results. Finally, our findings, in conjunction with measurements made over 50 years ago, further support that the formerly assigned "anomalous"/) N2-phase is in fact the long-established gamma -N2 phase.

The key parameters governing the mechanical stability of highly porous materials such as metal-organic frameworks (MOFs) are yet to be clearly understood. This study focuses on the role of the linker connectivity by investigating the mechanical stability of MIL-100(Cr), a mesoporous MOF with a hierarchical structure and a tritopic linker, and comparing it to MIL-101(Cr) having instead a ditopic linker. Using synchrotron X-ray diffraction and infrared spectroscopy, we investigate the high-pressure behavior of MIL-100(Cr) with both solid and fluid pressure transmitting media (PTM). In the case of a solid medium, MIL-100(Cr) undergoes amorphization at about 0.6 GPa, while silicone oil as a PTM delays amorphization until 12 GPa due to the fluid penetration into the pores. Both of these values are considerably higher than those of MIL-101(Cr). MIL-100(Cr) also exhibits a bulk modulus almost ten times larger than that of MIL-101(Cr). This set of results coherently proves the superior stability of MIL-100(Cr) under compression. We ascribe this to the higher connectivity of the organic linker in MIL-100(Cr), which enhances its interconnection between the metal nodes. These findings shed light on the importance of linker connectivity in the mechanical stability of MOFs, a relevant contribution to the quest for designing more robust MOFs.

Material characterization and investigation are the basis for improving the performance of electrochemical devices. However, many compounds with electrochemical applications are sensitive to atmospheric gases and moisture; therefore, even their characterization should be performed in a controlled atmosphere. In some cases, it is impossible to execute such investigations in a glove box, and, therefore, in the present work, an air-tight 3D printed cell was developed that preserves samples in a controlled atmosphere while allowing spectroscopic measurements in reflectance geometry. Equipped with a cheap 1 mm thick CaF2 optical window or a more expensive 0.5 mm thick ZnS window, the cell was used for both optical photothermal infrared and Raman spectroscopy measures; imaging of the samples was also possible. The far-infrared range reflectance measurements were performed with a cell equipped with a diamond window.

We measured the far-infrared reflectivity of a KH2PO4 single crystal up to pressures of 2 GPa in the ferroelectric and paraelectric phases. We find that the nu4 vibrational mode of the PO4 tetrahedron is strongly affected by the applied pressure. At ambient pressure this phonon is destabilized by the presence of the H ions and hence shows a highly damped character, beyond the phonon propagation threshold. Applying a pressure close to 0.6 GPa makes this phonon clearly underdamped. Its behavior closely follows the soft-mode behavior observed in Raman spectroscopy. Our results solve a long standing open problem, demonstrating that the nu4 mode is the excitation mediating the coupling of the hydrogen network to the lattice modes that create the ferroelectic polarization in KH2PO4.

The coexistence of the charge-density wave (CDW) and superconducting phases and their tunability under external pressure remains one of the key points in understanding the electronic structure of A V 3 Sb 5 ( A = K, Rb, Cs) kagome metals. Here, we employ synchrotron-based infrared spectroscopy assisted by density-functional calculations to study the pressure evolution of the electronic structure at room temperature up to 17 GPa experimentally. The optical spectrum of CsV 3 Sb 5 is characterized by the presence of localized carriers seen as a broad peak at finite frequencies in addition to the conventional metallic Drude response. The non-monotonic pressure dependence of this low-energy peak reflects the re-entrant behavior of superconductivity and may be interpreted in terms of electron-phonon coupling, varying with the growth and shrinkage of the Fermi surface under pressure. Moreover, drastic modifications in the low-energy interband absorptions are observed upon the suppression of CDW. These changes are related to the upward shift of the Sb2 p x + p y band that eliminates part of the Fermi surface around the M -point, whereas band saddle points do not move significantly. These observations shed new light on the mixed electronic and lattice origin of the CDW in CsV 3 Sb 5 .

The morphological changes of Si nanowires (Si NWs) cycled in 1:1 ethylene–carbonate (EC)/diethyl–carbonate (DEC) with or without different additives, fluoroethylene carbonate (FEC) or vinylene carbonate (VC), as well as the composition of the deposited solid–electrolyte interphase layer, are investigated by a combination of experimental microscopic and spectroscopic techniques. Scanning electron microscopy and optical spectroscopy highlight that the NW morphology is better preserved in samples cycled in the presence of FEC and VC additives compared to the additive-free electrolyte. However, only the use of FEC is capable of slightly mitigating the amorphization of silicon upon cycling. The solid electrolyte interphase (SEI) formed over the Si NWs cycled in the additive-free electrolyte is richer in organic and inorganic carbonates compared to the SEI grown in the presence of the VC and FEC additives. Furthermore, both additives are able to remarkably limit the degradation of the LiPF6 salt. Overall, the use of the FEC-additive in the carbonate-based electrolyte promotes both morphological and structural resilience of the Si NWs upon cycling thanks to the optimal composition of the SEI layer.

We present a high-pressure investigation of the semiconductor-to-metal transition in MoS2 and WS2 carried out by synchrotron-based far-infrared spectroscopy, to reconcile the controversial estimates of the metallization pressure found in the literature and gain new insight into the mechanisms ruling this electronic transition. Two spectral descriptors are found indicative of the onset of metallicity and of the origin of the free carriers in the metallic state: the absorbance spectral weight, whose abrupt increase defines the metallization pressure threshold, and the asymmetric line shape of the E1u peak, whose pressure evolution, interpreted within the Fano model, suggests the electrons in the metallic state originate from n-type doping levels. Combining our results with those reported in the literature, we hypothesize a two-step mechanism is at work in the metallization process, in which the pressure-induced hybridization between doping and conduction band states drives an early metallic behavior, while the band gap closes at higher pressures.

The first quantitative determinations of heterogeneoustwo-componentreaction rates in single crystals under high pressure are reported.The rate of arsenolite inclusion compound with hydrogen, As4O6 & BULL;2H(2), formation on the surface of anarsenolite single crystal has been determined at 1.47 (5) and 1.37(5) GPa via synchrotron Fourier transform infrared spectroscopy. Athin plate of arsenolite has been completely transformed into theinclusion compound within 1 and 11 h, respectively. The inclusioncompound growth rate was found to be linear with a slope of 7.7 (4)& mu;m/h at 1.47 (5) GPa, indicating that reaction at the As4O6/As4O6 & BULL;2H(2) phase boundary is rate-limiting. The kinetics of As4O6 & BULL;2H(2) growth at 1.37 (5) GPa exhibits two domainsof linear growth with slopes of 0.25 (1) and 1.2 (1) & mu;m/h. Incidentally,a method of growing thin plates of As4O6 singlecrystals via spatial confinement is presented. This work shows thatthe single-crystal study of two-component reaction kinetics in diamondanvil cells is possible and presents one of the feasible ways to doit in a quantitative manner.

Sample-return missions allow the study of materials collected directly from celestial bodies, unbiased by atmospheric entry effects and/or terrestrial alteration and contamination phenomena, using state-of-the-art techniques which are available only in a laboratory environment—but only if the collected material stays pristine. The scarcity of outer-space unaltered material recovered until now makes this material extremely precious for the potential scientific insight it can bring. To maximize the scientific output of current and future sample-return missions, the scientific community needs to plan for ways of storing, handling, and measuring this precious material while preserving their pristine state for as long as the ‘invasiveness’ of measurements allows. In July 2021, as part of the Hayabusa2 (JAXA) “Stone” preliminary examination team, we received several microscopic particles from the asteroid Ryugu, with the goal of performing IR hyper-spectral imaging and IR micro-tomography studies. Here, we describe the sample transfer, handling methods and analytical pipeline we implemented to study this very precious material while minimizing and surveilling their alteration history on Earth.