Pressure-induced Variations Research Articles

Pressure-Dependent Electronic Superlattice in the Kagome Superconductor CsV_{3}Sb_{5}.

We present a high-resolution single crystal x-ray diffraction study of kagome superconductor CsV_{3}Sb_{5}, exploring its response to variations in pressure and temperature. We discover that at low temperatures, the structural modulations of the electronic superlattice, commonly associated with charge-density-wave order, undergo a transformation around p∼0.7 GPa from the familiar 2×2 pattern to a long-range-ordered modulation at wave vector q=(0,3/8,1/2). Our observations align with inferred changes in the charge-density-wave pattern from prior transport and nuclear-magnetic-resonance studies, providing new insights into these transitions. Interestingly, the pressure-induced variations in the electronic superlattice correlate with two peaks in the superconducting transition temperature as pressure changes, hinting that fluctuations within the electronic superlattice could be key to stabilizing superconductivity. However, our findings contrast with the minimal pressure dependency anticipated by abinitio calculations of the electronic structure. They also challenge prevailing scenarios based on a Peierls-like nesting mechanism involving Van Hove singularities.

Pressure-induced structural variations and mechanical behavior of silicate glasses: Role of aluminum and sodium

Pressure-induced structural variations and mechanical behavior of silicate glasses: Role of aluminum and sodium

Refractivity corrected distance measurement using the intermode beats derived from a supercontinuum.

Simultaneous distance measurements on two or more optical wavelengths enable dispersion-based correction of deviations that result from insufficient knowledge of the refractive index along the signal propagation path. We demonstrate a supercontinuum-based approach for highly accurate distance measurements suitable for such an inline refractivity compensation. The distance is estimated from the phase delay observations on the intermode beats. We use a supercontinuum (SC) coherently broadened from a 780 nm frequency comb and spanning the spectral range of 570-970 nm. Experiments are performed on the 590 and 890 nm wavelength bands filtered from the SC spectrum. Results show distance measurements with standard deviations of around 0.01 mm at 50 m, and a distance-dependent component below 0.2 ppm on the individual spectral bands. Distance residuals compared to a reference interferometer are on the order of 0.1 ppm for displacements up to 50 m. Controlled pressure-induced refractivity variations are created over a length of 15 m, resulting in an optical path length change of 0.4 mm. Using the two-color method, we demonstrate refractivity-corrected distance measurement with a standard deviation of around 0.08 mm for a 60 s averaging window. The current experimental configuration can be easily extended to distance measurements on more than two wavelengths. The results highlight its potential for practical long-distance measurements through inline refractivity compensation.

Accurate modeling and measurement of pressure-induced group velocity dispersion variations in anti-resonant hollow-core fibers.

Precise control of group velocity dispersion (GVD) by pressure in a gas-filled hollow-core fiber (HCF) is of essential importance for many gas-based nonlinear optical applications. To accurately calculate the pressure-induced dispersion variations (∂β2/∂p) in anti-resonant types of HCF, an analytical model combining the contribution of the gas material, capillary waveguide, and cladding resonances is developed, with an insightful physical picture. Broadband (∼1000 nm) GVD measurements in a single-shot manner realize accuracy and precision as low as 0.1 ps2/km and 2 × 10-3 ps2/km, respectively, and validate our model. Consistent with our model, a pronounced negative ∂β2/∂p is observed experimentally for the first time, to our knowledge. Our model can also be extended to other HCFs with cladding resonances in predicting ∂β2/∂p, such as in photonic bandgap types of HCF.

Airborne acoustic emission of an abrasive waterjet cutting system as means for monitoring the jet cutting capability

Abrasive waterjet cutting is a manufacturing technology making use of a high-speed waterjet with abrasive particles in suspension, for cutting materials with different mechanical properties. Product quality requirements are pushing towards an improvement of tracking and stabilization methods of the relevant process variables. Amongst those, the jet kinetic power defines the cutting capability and has a significant impact on the final cut features. This variable is subject to relevant fluctuations versus time. Besides, the current state of the art does not provide means for its in-line monitoring. The aim of this contribution is to monitor the airborne acoustic emission of an abrasive waterjet cutting head and investigate its correlation with the jet kinetic power. The investigation is carried out by means of factorial studies, in which the jet is fired at various water pressures and abrasive feed rates, providing different kinetic powers. The acoustic emission is synchronously monitored by means of a condenser microphone, installed on the cutting head. Data at frequencies above 40 kHz is found to constitute a robust and selective acoustic signature of the airborne jet. The acoustic signature is proven to be an effective in-line indicator of the jet kinetic power and its pressure-induced variations, whilst abrasive-induced variations remain undetected. A calibration procedure is presented, for translating the acoustic data into a jet kinetic power. The method is validated by means of further experiments that envisage its deployment in a real scenario. Overall, the presented method constitutes a robust tool for monitoring pressure-induced variations of the jet cutting capability.

Pressure-induced variations of medium-range order in B2O3 glasses

Pressure-induced variations of medium-range order in B2O3 glasses

The superconducting transition temperatures of C–S–H based on inter-sublattice S−H4-tetrahedron electronic interactions

Significant characteristics of the superconducting transitions reported for carbonaceous sulfur hydride [Snider et al., Nature 585, 373 (2020)] are the exceptionally abrupt onset temperatures and their marked increase toward room temperature at high pressures. Theoretical and experimental studies addressing the superconducting composition and structure have thus far returned mixed results. One possibility, consistent with the experimentally suggested stoichiometry of CSHx, is the theoretically discovered compressed I4¯3m CSH7 structure [Sun et al., Phys. Rev. B 101, 174102 (2020)], which comprises a sublattice similar to Im3¯m H3S with CH4 intercalates. Positing an electronic genesis of the superconductivity, a model is presented in analogy with earlier work on superconductivity in Im3¯m H3S, in which pairing is induced via purely electronic Coulomb interactions across the mean distance ζ between the S and H4-tetrahedra enclosing C. Theoretical superconducting transition temperatures for I4¯3m CSH7 are derived as TC0 = (2/3)1/2σ1/2β/aζ, where β = 1247.4 Å2 K is a universal constant, σ is the participating charge fraction, and a is the lattice parameter. Analysis suggests persistent bulk superconductivity with a pressure-dependent σ, increasing from σ = 3.5, determined previously for Im3¯m H3S, to σ = 7.5 at high pressure owing to additionally participating C–H bond electrons. With a and ζ determined by theoretical structure, TC0 = 283.6 ± 3.5 K is predicted at 267 ± 10 GPa, in excellent agreement (within uncertainty) with the corresponding experimental TC = 287.7 ± 1.2 K. Pressure-induced variations in σ combined with experimental uncertainties in pressure yield overall average (TC − TC0) = (−0.8 ± 3.5) K.

Ultrafast Spectroscopic Analysis of Pressure-Induced Variations of Excited-State Energy and Intramolecular Proton Transfer in Semi-Aliphatic Polyimide Films.

The relationship between the photoexcitation dynamics and the structures of semi-aliphatic polyimides (3H-PIs) was investigated using ultrafast fluorescent emission spectroscopy at atmospheric and increased pressures of up to 4 GPa. The 3H-PI films exhibited prominent fluorescence with extremely large Stokes shifts (Δν > 10 000 cm-1) through an excited-state intramolecular proton transfer (ESIPT) induced by keto-enol tautomerism at the isolated dianhydride moiety. The incorporation of bulky -CH3 and -CF3 side groups at the diamine moiety of the PIs increased the quantum yields of the ESIPT fluorescence owing to an enhanced interchain free volume. In addition, 3H-PI films emitted another fluorescence at shorter wavelengths originating from closely packed polyimide (PI) chains (in aggregated forms), which was mediated through a Förster resonance energy transfer (FRET) from an isolated enol form into aggregated forms. The FRET process became more dominant than the ESIPT process at higher pressures owing to an enhancement of the FRET efficiency caused by the increased dipole-dipole interactions associated with a densification of the PI chain packing. The efficiency of the FRET rapidly increased by applying pressure up to 1 GPa owing to an effective compression of the interchain free volume and additionally gradually increased at higher pressures owing to structural and/or conformational changes in the main chains.

Analysis of Pressure-induced Variations in the Crystalline Structures of Polyimides Having Flexible Linkages by Wide-Angle X-ray Diffraction

Analysis of Pressure-induced Variations in the Crystalline Structures of Polyimides Having Flexible Linkages by Wide-Angle X-ray Diffraction

Correlative Experimental and Theoretical Investigation of the Angle-Resolved Composition Evolution of Thin Films Sputtered from a Compound Mo2BC Target

The angle-resolved composition evolution of Mo-B-C thin films deposited from a Mo2BC compound target was investigated experimentally and theoretically. Depositions were carried out by direct current magnetron sputtering (DCMS) in a pressure range from 0.09 to 0.98 Pa in Ar and Kr. The substrates were placed at specific angles α with respect to the target normal from 0 to ±67.5°. A model based on TRIDYN and SIMTRA was used to calculate the influence of the sputtering gas on the angular distribution function of the sputtered species at the target, their transport through the gas phase, and film composition. Experimental pressure- and sputtering gas-dependent thin film chemical composition data are in good agreement with simulated angle-resolved film composition data. In Ar, the pressure-induced film composition variations at a particular α are within the error of the EDX measurements. On the contrary, an order of magnitude increase in Kr pressure results in an increase of the Mo concentration measured at α = 0° from 36 at.% to 43 at.%. It is shown that the mass ratio between sputtering gas and sputtered species defines the scattering angle within the collision cascades in the target, as well as for the collisions in the gas phase, which in turn defines the angle- and pressure-dependent film compositions.

Pressure-Induced Variations of Aggregation Structures in Colorless and Transparent Polyimide Films Analyzed by Optical Microscopy, UV-Vis Absorption, and Fluorescence Spectroscopy.

Pressure-induced variations in the main chain and aggregation structures of colorless and transparent semialiphatic polyimide (PI) films were investigated by optical microscopy, UV-vis absorption, and fluorescence spectroscopy up to 8 GPa. Upon application of pressures up to 2 GPa, a gradual volumetric compression was clearly observed by microscopy, and definite bathochromic shifts of locally excited (LE) absorption bands were detected, which was attributed to the compression of interchain free volume and enhanced intermolecular interactions. In addition, a significant reduction in fluorescence intensity was observed for PIs with quasilinear structures below 2 GPa due to enhanced energy transfer in the excited states caused by the densification of PI chain packing. In contrast, the volumetric compression of the PI films and bathochromic shifts of the LE absorption bands were gradually reduced at pressures above 2 GPa. The former is closely correlated with the bulkiness and flexibility of the alicyclic diamine structure. The latter reflects the intense compression stress generated around the dianhydride moiety, associated with the deformability and in-plane orientation of the main PI chains. High-pressure experiments on PI films are beneficial to investigate variations in aggregation structures and local electronic structures of PI chains induced by dense molecular packing and enhanced intermolecular interactions.

Magnetic interactions in a proposed diluted magnetic semiconductor (Ba1−xKx)(Zn1−yMny)2P2**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0302903), the National Natural Science Foundation of China (Grant Nos. 11774422 and 11774424), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant Nos. 14XNLQ03 and 16XNLQ01).

By using first-principles electronic structure calculations, we have studied the magnetic interactions in a proposed BaZn2P2-based diluted magnetic semiconductor (DMS). For a typical compound Ba(Zn0.944Mn0.056)2P2 with only spin doping, due to the superexchange interaction between Mn atoms and the lack of itinerant carriers, the short-range antiferromagnetic coupling dominates. Partially substituting K atoms for Ba atoms, which introduces itinerant hole carriers into the p orbitals of P atoms so as to link distant Mn moments with the spin-polarized hole carriers via the p–d hybridization between P and Mn atoms, is very crucial for the appearance of ferromagnetism in the compound. Furthermore, applying hydrostatic pressure first enhances and then decreases the ferromagnetic coupling in (Ba0.75K0.25)(Zn0.944Mn0.056)2P2 at a turning point around 15 GPa, which results from the combined effects of the pressure-induced variations of electron delocalization and p–d hybridization. Compared with the BaZn2As2-based DMS, the substitution of P for As can modulate the magnetic coupling effectively. Both the results for BaZn2P2-based and BaZn2As2-based DMSs demonstrate that the robust antiferromagnetic (AFM) coupling between the nearest Mn–Mn pairs bridged by anions is harmful to improving the performance of these II–II–V based DMS materials.

Direct Printing of Stretchable Elastomers for Highly Sensitive Capillary Pressure Sensors.

We demonstrate the successful fabrication of highly sensitive capillary pressure sensors using an innovative 3D printing method. Unlike conventional capacitive pressure sensors where the capacitance changes were due to the pressure-induced interspace variations between the parallel plate electrodes, in our capillary sensors the capacitance was determined by the extrusion and extraction of liquid medium and consequent changes of dielectric constants. Significant pressure sensitivity advances up to 547.9 KPa−1 were achieved. Moreover, we suggest that our innovative capillary pressure sensors can adopt a wide range of liquid mediums, such as ethanol, deionized water, and their mixtures. The devices also showed stable performances upon repeated pressing cycles. The direct and versatile printing method combined with the significant performance advances are expected to find important applications in future stretchable and wearable electronics.

First-principle studies on the influence of anisotropic pressure on the physical properties of aluminum nitride

In this work, we performed extensive first-principle studies to discuss the effect of uniaxial and biaxial mechanical pressure on the structural and physical properties of AlN piezoelectric material, including the longitudinal elastic constant (C33), piezoelectric constant (e33), static dielectric constant (ε33), and mass density (ρ). In particular, we give the relationship between the paramters mentioned above and the longitudinal acoustic wave velocity (V) under anisotropic pressure. Our results show that the applied uniaxial or biaxial pressure in the basal plane has a more obvious influence on physical properties of AlN than the uniaxial pressure along hexagonal axis. The pressure-induced variations of C33, e33 and ρ significantly change the V value, whereas the effect of ε33 on V is negligible. Our theoretical results provide useful information for the performance predictions of electro-acoustic mechanics sensors, such as FBAR mechanical sensors, based on the intrinsic properties of piezoelectric materials.

Filling of High-Concentration Monoclonal Antibody Formulations: Investigating Underlying Mechanisms That Affect Precision of Low-Volume Fill by Peristaltic Pump.

Vial and syringe filling by peristaltic pump is considered a well-established manufacturing process and has been implemented by numerous contract manufacturing organizations and biopharmaceutical companies. However, its technical details and associated critical process parameters on fill weight precision are rarely published. Such information on high-concentration/viscosity formulation filling is particularly lacking. This study aimed to identify critical filling parameters that dictate a tight control on fill weight precision. The findings of this study indicate that mitigating suck-back height variation is the key to achieving improved fill weight precision. Liquid properties, the influence of liquid/nozzle interactions, and pressure variations during suck-back are inherent to fill weight variations. Optimizing fill weight precision by manipulating pump system parameters is not a root-cause solution. The outcomes of this study will benefit scientists and engineers who develop pre-filled syringe/vial products by providing a better understanding of high-concentration formulation filling principles and challenges.

Pressure-induced variations of MLCT and ligand-centered luminescence spectra in square-planar platinum(II) complexes

Solid-state luminescence spectra of five crystalline platinum(II) complexes at variable pressure and temperature are presented and compared. Maxima occur between 14 000 cm−1 and 15 600 cm−1 (approximately 700–640 nm) at ambient temperature and pressure. Spectra can be broad bands, characteristic of MLCT transitions, or vibronically structured, characteristic of intraligand transitions. Both pressure and temperature variations can lead to distinctive changes in the luminescence spectra that differ between these two types of transitions. MLCT band maxima show shifts on the order of −20 cm−1/kbar to lower energy; in contrast, ligand-centered luminescence bands do not show significant shifts between ambient pressure and 40 kbar.

Temperature and pressure variations of d-d luminescence band maxima of bis(pyridylalkenolato)palladium(II) complexes with different ligand substituents: opposite-signed trends.

Luminescence spectra of two d(8)-configured bis(pyridylalkenolato)palladium(ii) complexes, [Pd{PyCHC(C3F7)O}2] and [Pd{PyCHC(CH3)O}2], are presented at variable temperature and pressure. Bands are assigned as d-d transitions. The heptafluoropropyl and methyl substituents on the ligands have different steric demands, influencing luminescence spectra. Broad bands with maxima at approximately 12 700 cm(-1) (790 nm) for ligands with heptafluoropropyl substituents and 12,100 cm(-1) (830 nm) for ligands with methyl substituents and widths of approximately 2100 cm(-1) for both complexes are observed at 80 K. Quenching of the luminescence is observed as temperature increases. The maxima of [Pd{PyCHC(C3F7)O}2] show a shift of -0.9 ± 0.1 cm(-1) K(-1) due to broadening of the spectra to lower energy. The luminescence maxima of [Pd{PyCHC(CH3)O}2] shift in the opposite direction by +7.2 ± 0.7 cm(-1) K(-1). Shifts with different signs are also obtained from variable-pressure luminescence spectra, with values of +13 ± 2 cm(-1) kbar(-1) and -15 ± 7 cm(-1) kbar(-1) for [Pd{PyCHC(C3F7)O}2] and [Pd{PyCHC(CH3)O}2], respectively. The pressure-induced decrease is unusual and likely caused by intermolecular interactions involving the palladium(ii) center and a vinylic proton of a neighboring complex.

Pressure-induced wall thickness variations in multi-layered wall of a pollen tube and Fourier decomposition of growth oscillations.

The augmented growth equation introduced by Ortega is solved for the apical portion of the pollen tube as an oscillating volume, which we approach in the framework of a two-fluid model in which the two fluids represent the constant pressure and the fluctuating features of the system. Based on routine Fourier analysis, we calculate the energy spectrum of the oscillating pollen tube, and discuss the resonant frequency problem of growth rate oscillations. We also outline a descriptive model for cell wall thickness fluctuations associated with small, yet regular variations (~ 0.01 MPa) observed in turgor pressure. We propose that pressure changes must lead to the sliding of wall layers, indirectly resulting in a wave of polarization of interlayer bonds. We conclude that pollen tube wall thickness may oscillate due to local variations in cell wall properties and relaxation processes. These oscillations become evident because of low amplitude/high frequency pressure fluctuations δP being superimposed on turgor pressure P. We also show that experimentally determined turgor pressure oscillates in a strict periodical manner. A solitary frequency f0 ≈ 0.066 Hz of these (~ 0.01 MPa in magnitude) oscillations for lily pollen tubes was established by the discrete Fourier transform and Lorentz fit.

Pressure-induced stacking sequence variations in gold from first principles

Pressure-induced stacking sequence variations of gold are predicted from first-principles calculations. At the static condition, the ABC stacking in the face-centered-cubic (fcc) phase changes into ABCACB above at least 200 GPa, and then into ABAC corresponding to the double hexagonal-close-packed structure. By further compression, the hexagonal-close-packed (hcp) structure with the AB stacking emerges as the most stable structure of all the stacking structures. This sequence of the transitions shows a step-by-step increase of the hexagonality over a wide pressure range. The calculations of phonon free energy indicate that the stable region of the intermediate stacking structures between fcc and hcp such as ABCACB or ABAC gets to be narrow with increase of temperature and fcc directly transforms into hcp above 400 K. This direct transition from fcc to hcp is qualitatively consistent with the earlier experimental observations.

A first-principles study of the structural, electronic and elastic properties of solid nitromethane under pressure

The structural, electronic and elastic properties of solid nitromethane are investigated under pressure by performing first-principles density functional theory (DFT) calculations within the generalized gradient approximation (GGA) and the local density approximation (LDA). The obtained ground state structure properties are found to be consistent with existing experimental and theoretical results. The pressure-induced variations of structure parameters (a, b, c and V) indicate that the solid nitromethane has an anisotropic compressibility, and the compression along the c direction is more difficult than along a and b directions. From the vibration curves of intermolecular bond length and bond angle, we find that the C-N bond is the most sensitive among these bonds under pressure, suggesting that the C-N bonds may be broken first under external loading. The influence of pressure on the electronic properties of solid NM has been studied, indicating that solid NM is an insulating compound with a large indirect band gap and tends to be a semiconductor with increasing pressure. Finally, we predict the elastic constants and their pressure dependence for the solid NM with the bulk modulus, Young’s modulus, shear modulus and the Poisson’s ratio derived.