High-pressure Investigations Research Articles

Structure Evolution and Optical Tuning of One-Dimensional Post-perovskite (TDMP)PbBr4 under High Pressure.

Optimizing the structure and tuning the optical properties in low-dimensional organic-inorganic halide perovskites are crucial to practical applications for stable solid-state lighting. Herein, we performed high-pressure investigations on one-dimensional (1D) postperovskite (TDMP)PbBr4 (TDMP = trans-2,5-dimethylpiperaziniium), and structure and optical properties under pressure are studied. (TDMP)PbBr4 exhibits color tunable emission from cool white light to yellow orange as the pressure increases from atmospheric pressure to 20.0 GPa. It was found that high pressure would facilitate trapping the free exciton (free exciton) to form a self-trapped exciton (STE) state due to increased electron-phonon interaction, thus enhancing STE emission in the pressure range of 4.0-7.0 GPa. At above 7.0 GPa, the STE emission is quenched, which is due to the phonon-assisted nonradiative relaxation. Meanwhile, (TDMP)PbBr4 displays reversible piezochromism from colorless to yellow under pressure as a result of the compound undergoing a reversible structural transformation. This work provides an insightful perspective on revealing the relationship between structure and optical properties of 1D postperovskites under high pressure.

High pressure ferroelectric-like semi-metallic state in Eu-doped BaTiO3.

We have conducted a detailed high-pressure (HP) investigation on Eu-doped BaTiO3 using angle-resolved x-ray diffraction, Raman spectroscopy, and dielectric permittivity measurements. The x-ray diffraction data analysis shows a pressure-induced structural phase transition from the ambient tetragonal to the mixed cubic and tetragonal phases above 1.4GPa. The tetragonality of the sample due to the internal deformation of the TiO6 octahedra caused by the charge difference from Eu doping cannot be lifted by pressure. Softening, weakening, and disappearance of low-frequency Raman modes indicate ferroelectric tetragonal to the paraelectric cubic phase transition. However, the pressure-induced increase in the intensity of [E(LO), A1(LO)] and the octahedral breathing modes indicate that the local structural inhomogeneity remains in the crystal and is responsible for spontaneous polarization in the sample. The low-frequency electronic scattering response suggests pressure-induced carrier delocalization, leading to a semi-metallic state in the system. Our HP dielectric constant data can be explained by the presence of pressure-induced localized clusters of microscopic ferroelectric ordering. Our results suggest that the HP phase coexistence leads to a ferroelectric-like semi-metallic state in Eu-doped BaTiO3 under extreme quantum limits.

Pressure-controlled free exciton and self-trapped exciton emission in quasi-one-dimensional hybrid lead bromides

Hybrid metal halides represent a novel type of semiconductor light emitters with intriguing excitonic emission properties, including free exciton emission and self-trapped exciton emission. Achieving precise control over these two excitonic emissions in hybrid metal halides is highly desired yet remains challenging. Here, the complete transformation from intrinsically broadband self-trapped exciton emission to distinctively sharp free exciton emission in a quasi-one-dimensional hybrid metal halide (C2H10N2)8[Pb4Br18]·6Br with a ribbon width of n = 4, is successfully achieved based on high-pressure method. During compression, pressure-induced phonon hardening continuously reduces exciton–phonon coupling, therefore suppressing excitonic localization and quenching the original self-trapped exciton emission. Notably, further compression triggers excitonic delocalization to induce intense free exciton emission, accompanied with reduced carrier effective masses and improved charge distribution. Controlled high-pressure investigations indicate that the ribbon width of n > 2 is necessary to realize excitonic delocalization and generate free exciton emissions in similar quasi-one-dimensional hybrid metal halides. This work presents an important photophysical process of excitonic transitions from self-trapped exciton emission to free exciton emission in quasi-one-dimensional hybrid metal halides without chemical regulation, promoting the rational synthesis of hybrid metal halides with desired excitonic emissions.

(Invited) Carbon Phase Adjustment by Multi-Configuration Ligand in Endohedral Metallofullerene Derivatives Gd@C82(morpholine)7 Under High Pressure

Metallofullerenes present an ideal research object for developing new carbon structures with improved properties under high pressure. In this presentation, high pressure investigation is realized on metallofullerene derivatives (Gd@C82(morpholine)7) by applying in situ synchrotron XRD, Raman, and IR spectroscopy, combined with high pressure density functional theory (DFT) calculations. The regulations of multi-configuration morpholine ligands avoid the direct collapse of the carbon cages commonly happened to fullerenes, making the fine structure transformation possible for the first time, including ligand configuration exchange, anisotropic shrinkage of cage, new constructed bonds, and even the encaged metal’s movement with increasing pressure. The charge-transfer principle as the beneath driving force of structural transition is found. These findings demonstrate that multi-configuration ligand maps an innovative strategy for phase transition control of metallofullerenes under high pressure, thus providing deep insight, step by step, into the phase transition mechanism of these hybrid molecular systems on molecular level.

Compressibility Studies of Copper Selenides Obtained by Cation Exchange Reaction Revealing the New CsCl Phase.

In this study, we conducted a high-pressure investigation of Cu2-xSe nanostructures with pyramid- and plate-like morphologies, created through cation exchange from zinc-blende CdSe nanocrystals and wurtzite CdSe nanoplatelets respectively. Using a diamond anvil cell setup at the APS synchrotron, we observed the phase transitions in the Cu2-xSe nanostructures up to 40 GPa, identifying a novel CsCl-type lattice with Pm3̅m symmetry above 4 GPa. This CsCl-type structure, previously unreported in copper selenides, was partially retained after decompression. Our results indicate that the initial crystalline structure of CdSe does not affect the stability of Cu2-xSe nanostructures formed via cation exchange. Both morphologies of Cu2-xSe sintered under compression, potentially contributing to the stabilization of the high-pressure phase through interfacial defects. These findings are significant for discovering new phases with potential applications in future technologies.

In situ investigation of the atomic structure of carbonate-silicate liquids at high pressure-temperature and spectroscopic characterization of the recovered quenched glasses

Carbonate-silicate melts that originate in Earth's interior are described as transitional melts which possess compositions intermediate between carbonatitic and basaltic end members. The covariation of key oxides between carbonatite and basalt (e.g., 10–35 wt% SiO2 and 40–10 wt% CO2, respectively) is expected to have a strong effect on liquid properties. However, due to their paucity both in the record of terrestrial rocks and as quenched glasses, their molecular structure has remained poorly explored to date. We investigated the atomic structure of a synthetic carbonate-silicate liquid with chemical composition within the CaO-MgO-Al2O3-SiO2-FeO-Na2O-ClO−-CO2 oxide system having 18.28 wt% SiO2 and 22.54 wt% CO2 using multi-angle energy dispersive X-ray diffraction at pressures (P) and temperatures (T) of 1.4 GPa/1815 °C, 2.6 GPa/1865 °C, 4.3 GPa/1990 °C, 4.4 GPa/1950 °C. The results show that the intermediate range ordering of the structure decreases with an increase of both P and T. Based on this study, the carbonate-silicate magmas at upper mantle P-T conditions are expected to increase their viscosities during their ascent through the mantle as a result of increasing intermediate range ordering upon cooling and decompression. Additionally, spectroscopic measurements were carried out on the quenched glasses at ambient pressure using micro-Raman as well as micro-FTIR in reflection and transmission modes in the mid infrared range. High pressure investigation using micro-FTIR was also conducted. The distribution of Qn species obtained by deconvolution of the Raman spectra within the aluminosilicate region confirms the depolymerized nature of the quenched glasses as inferred by the low viscosities of the corresponding liquids; peculiar characteristics of the C vibrations would suggest a distorted environment surrounding the network modifying CO32− anion. No evidence of molecular CO2 was detected. Notably, we find evidence of both dissolved molecular CO and CO linked to a metal cation forming carbonyl complexes in the quenched glasses at P-T-fo2 conditions compatible with a hot Archean upper mantle. This suggests a role for carbonate-silicate magmas as carriers of reduced gaseous C-O-H species towards the early atmosphere along with the mobilization of PGE-elements.

A novel method for determining the resistivity of compressed superconducting materials

The measurement of resistivity in a compressed material within a diamond anvil cell presents significant challenges. The high-pressure experimental setup makes it difficult to directly measure the size changes induced by pressure in the three crystallographic directions of the sample. In this study, we introduce a novel and effective method that addresses these technical challenges. This method is anticipated to offer a valuable foundation for high-pressure investigations on quantum materials, particularly those with anisotropic layered structures.

Pressure and Composition Effects on a Common Nanoparticle Ligand-Solvent Pair.

The effect of pressure on the properties of nanoparticles is a growing area of investigation. These measurements are typically performed in a colloidal suspension; however, pressure-induced changes in the interactions between the nanoparticle surface and the solvent are often neglected. Here, we report vibrational spectroscopy of a common nanoparticle ligand, 1-dodecanethiol, and a common solvent, toluene, under pressure. We find that the pressure-induced phase change of the 1-dodecanethiol is altered by the presence of toluene and that change depends on the concentration of the free ligand in the solution. At near-equal concentrations, phase segregation is observed and the dodecanethiol crystallizes independently from the toluene. On the other hand, at unequal concentrations, concerted phase transitions are observed in the dodecanethiol and toluene, and a disordered conformation of dodecanethiol is maintained under much higher pressures. These results shed light on the pressure-induced changes in intermolecular interactions between nanoparticle ligands and solvents, which must be considered in the design of high-pressure investigations of colloidal nanoparticles.

High-pressure crystal growth and investigation of the metal-to-metal transition of Ruddlesden–Popper trilayer nickelates La4Ni3O10

Single crystals of Ruddlesden–Popper nickelates La4Ni3O10 were grown by means of the floating-zone technique at oxygen pressure of 20 bar. Our results reveal the effects of the annealing process under pressure on the crystal structure. We present the requirements for crystal growth and show how a reported ferromagnetic impurity phase can be avoided. The different growth and post-annealing processes result in two distinct phases P21/a and Bmab in which the metal-to-metal transitions occur at 152 K and 136 K, respectively.

Pressure-induced disorder and nanosizing inhibits superconductivity in In2Te3

The generation of disorder often gives rise to profound and irreversible physical phenomena. Here, we explore the influence of disorder on the superconducting properties of In2Te3 through comprehensive high-pressure investigations. Building upon previous findings, we investigated the progressive suppression of superconductivity in In2Te3 during the depressurization process: the increased disorder that ultimately leads to the complete disappearance of the superconducting state. Simultaneously, our high-pressure x-ray diffraction analysis reveals an irreversible structural phase transition. Furthermore, microstructure analysis using transmission electron microscopy clearly demonstrates both grain refinement and a substantial enhancement of disorder. These findings not only provide valuable insights into the mechanism by which disorder suppresses superconductivity, but also offer guidance for future advancements in the fabrication of atmospheric-pressure superconductors.

Pressure-Regulated Excitonic Transitions in Emergent Metal Halides.

ConspectusEmergent metal halides are generating significant interest as novel optical materials, and their diverse applications have brought them to the spotlight of chemistry and material science. The optical properties of semiconducting metal halides are fundamentally dominated by excitonic transitions, which refer to the complex processes of excitonic formation, self-trapping, as well as subsequent transitions of intersystem crossing (ISC) and internal conversion (IC). In this regard, high pressure has recently opened a new research dimension to regulate excitonic transitions in metal halides via continuous structural modulations, to understand the intriguing excitonic emissions from a new perspective. In this Account, we aim to rationalize the fundamental strategy for modulating and optimizing the optical properties of metal halides based on delicate exciton regulation via high-pressure method. First, the band gaps of metal halides that are directly related to the efficiency of excitonic formation, are accurately modulated through contraction, distortion, and destruction of metal-halogen polyhedra under compression. Then, considerable enhancement of self-trapped exciton emission is demonstrated by inducing proper polyhedral distortions via high-pressure method. Furthermore, the emission energy of metal halides could also be controllably and widely tuned through pressure-modulated excitonic transitions. Upon compression on different metal halides, excitonic IC is promoted with sufficient polyhedral distortions, and different sets of ISC could also be achieved. In the end, we emphasize the significance of high-pressure investigations in uncovering the complex excitonic transitions in emergent metal halides and predicting novel metal halides with desired optical properties at ambient conditions. It is expected that these discussions could inspire researchers in different fields to perform interdisciplinary high-pressure studies on novel functional materials.

Comparative high-pressure investigations of Ag2ZnSnS4 and Ag2CdSnS4 compounds

Quaternary kesterite-type (KS) compounds have attracted worldwide attention from the scientific community as promising materials for solar cells. On the route to optimizing their performance, the effect of stress and strain constitutes a critical factor when it comes to thin film applications. Following a recent theoretical study, we report here joint experimental and computational high-pressure investigations on the KS Ag2ZnSnS4 and wurtz–kesterite (WZ–KS)-type Ag2CdSnS4 compounds. Our results reveal that both materials undergo successive transformations, first into a GeSb-type and then toward a CrN-type modification at ambient temperature. Our theoretical calculations predict a metallic character for all Ag2ZnSnS4 and Ag2CdSnS4 high-pressure phases. In addition, structural disorder is observed in KS Ag2ZnSnS4 upon moderate compression, prior to its KS → GeSb-type transition. Decompression leads to the recovery of a disordered zinc blende-type structure in the latter, whereas Ag2CdSnS4 retains the disordered GeSb-type modification. The similarities and deviations from the archetypical KS Cu2ZnSnS4 are discussed.

Pressure-Driven Structural and Electronic Transitions in a Two-Dimensional Janus WSSe Crystal.

In this work, we presented the first report on the high-pressure structural stability and electrical transport characteristics in WSSe under different hydrostatic environments through Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy (HRTEM) coupled with first-principles theoretical calculations. For nonhydrostatic conditions, WSSe endured a phase transition at 15.2 GPa, followed by a semiconductor-to-metal crossover at 25.3 GPa. Furthermore, the bandgap closure was accounted for the metallization of WSSe as derived from theoretical calculations. Under hydrostatic conditions, ∼ 2.0 GPa pressure hysteresis was detected for the emergence of phase transition and metallization in WSSe because of the feeble deviatoric stress. Upon depressurization, the reversibility of the phase transition was substantiated by those of microscopic HRTEM observations under different hydrostatic environments. Our high-pressure investigation on WSSe advances the insightful understanding of the crystalline structure and electronic properties for the Janus transition-metal dichalcogenide (TMD) family and boosts prospective developments in functional devices.

High-pressure X-ray crystallographic investigation of chalcogen bonding

High-pressure X-ray crystallographic investigation of chalcogen bonding

Large volume multianvil cell assembly for hydrothermal synthesis and conversions up to 6.5 GPa and 400°C

ABSTRACT A multianvil cell assembly with octahedral edge length 25 mm has been adapted for high pressure investigations involving water-rich environments up to 6.5 GPa and 400°C. Water-rich samples are confined in Teflon containers with a volume up to 300 mm3. Applicability tests were performed between 250 and 400°C by investigating the transformation of amorphous titania particles close to the rutile–TiO2-II (∼5 GPa) phase boundary, and the transformation of amorphous silica particles close to the quartz–coesite (∼2.5 GPa) and coesite–stishovite (∼7 GPa) phase boundaries. The performed experiments employed 25.4 mm tungsten carbide anvils with a truncation edge length of 15 mm. The sample pressure at loads approaching 820 t was estimated to be around 6.5 GPa. The large volume multianvil cell is expected to have broad and varied application areas, ranging from the simulation of geofluids to hydrothermal synthesis and conversion/crystal growth in aqueous environments at gigapascal pressures.

Emergence of superconductivity in single-crystalline LaFeAsO under simultaneous Sm and P substitution

We report on the high-pressure growth, structural characterization, and investigation of the electronic properties of single-crystalline LaFeAsO co-substituted by Sm and P, in both its normal- and superconducting states. Here, the appearance of superconductivity is attributed to the inner chemical pressure induced by the smaller-size isovalent substituents. X-ray structural refinements show that the partial substitution of La by Sm and As by P in the parent LaFeAsO compound leads to a contraction in both the conducting Fe2(As,P)2 layers and the interlayer spacing. The main parameters of the superconducting state, including the critical temperature, the lower- and upper critical fields, as well as the coherence length, the penetration depth, and their anisotropy, were determined from magnetometry measurements on a single-crystalline La0.87Sm0.13FeAs0.91P0.09O sample. The critical current density (jc), as resulting from loops of magnetization hysteresis in the self-generated magnetic field, is 2 × 106 A/cm2 at 2 K. Overall, our findings illustrate a rare and interesting case of how superconductivity can be induced by co-substitution in the 1111 family. Such approach delineates new possibilities in the creation of superconductors by design, thus stimulating the exploration of related systems under multi-chemical pressure conditions.

Crystallographic structural variations in nano-crystalline Sc2O3 under pressure

The present manuscript reports high-pressure investigations on nano-crystalline Scandium Oxide (Sc2O3) through synchrotron angle dispersive x-ray diffraction technique (ADXRD) up to a pressure of ∼35.4 GPa using a diamond-anvil cell (DAC). The sample, having a cubic bixbyite structure at ambient conditions, underwent substantial changes in crystallographic parameters under the application of external pressure, while exhibiting phase stability i.e. does not undergo any structural phase transition up to 35.4 GPa. The lattice parameters and the unit cell volume decrease significantly with an increase in pressure, revealing the compressible nature of the crystal structure. The pressure-volume data is fitted using the third-order Birch-Murnaghan equation of state to calculate the bulk modulus and its first derivative, which yields zero pressure bulk modulus of 217(35) GPa, with = 12(4) and the corresponding ambient volume per unit molecule comes out to be 59.18(18) Å3.

The Promise and Challenge of High Pressure Macromolecular Crystallography

Since its introduction in the early 1970s, high pressure crystallography (HPX) has shown great potential for the investigation of different types of matter. Using diamond anvil cells, HPX is an emerging technique that has been rapidly implemented, making it available to biologists, and there is immense potential for utilizing this technique in biological systems in the future. At the molecular level, high-pressure crystallographic investigation provides information on structural characteristics that not only determine the native conformation of a protein but also the conformations with higher free-energy, thus revealing function-related structural changes and properties that can be modified as a result of pressurization. The increase in the number of crystal structures of different macromolecules determined under high pressure over the last five decades can be ascribed mainly to two factors: the emergence of high-pressure cells with very large, open angles, and the advent of third generation synchrotron sources. The use of high pressure crystallography as a research tool has been shown to contribute to the advancements in the basic fields of biochemistry (protein misfolding and aggregation), biophysics (protein stability), and biotechnology (food processing). Presently, with a growing interest in biomedicine and nanotechnology, this nonstandard method appears to be a valid instrument for probing more challenging and complex systems. In this review, we present the method, highlight a selection of recent applications, and describe challenges for high pressure macromolecular crystallography (HPMX).

Correction to ‘High pressure investigations on neutron irradiated ferroboron’

Correction to ‘High pressure investigations on neutron irradiated ferroboron’

Far-Infrared Signatures for a Two-Step Pressure-Driven Metallization in Transition Metal Dichalcogenides

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.