High-pressure X-ray Diffraction Research Articles

Early crystallization of amorphous selenium under high pressure studied by synchrotron XRD method

The amorphous selenium (a-Se) was studied via x-ray diffraction (XRD) under pressures ranging from ambient pressure up to 30 GPa at room temperature to study its high-pressure behavior. Two compressional experiments on a-Se samples, with and without heat treatment, respectively, were conducted. Contrary to the previous reports that a-Se crystallized abruptly at around 12 GPa, in this work we report an early partially crystallized state at 4.9 GPa before completing the crystallization at around 9.5 GPa based on in-situ high pressure XRD measurements on the a-Se with 70 °C heat treatment. In comparison, crystallization pressure on another a-Se sample without thermal treatment history was observed to be 12.7 GPa, consistent with the previously reported crystallization pressure. Thus, it is proposed in this work that prior heat treatment of a-Se can result in an earlier crystallization under high pressure, which helps to understand the possible mechanism caused by the previous controversial reports on pressure induced crystallization behavior in a-Se.

Superconductivity emerging from a pressurized van der Waals kagome material Pd3P2S8

Kagome materials have been reported to possess abundant and peculiar physical properties, which provide an excellent platform to explore exotic quantum states. We present a discovery of superconductivity in van der Waals material Pd3P2S8 composed of Pd kagome lattice under pressure. Pd3P2S8 displays superconductivity for those pressures where the semiconducting-like temperature dependence of the resistivity turns into a metallic one. Moreover, it is found that the increased pressure results in a gradual enhancement of superconducting transition temperature, which finally reaches 6.83 K at 79.5 GPa. Combining high-pressure x-ray diffraction, Raman spectroscopy and theoretical calculations, our results demonstrate that the observed superconductivity induced by high pressure in Pd3P2S8 is closely related to the formation of amorphous phase, which results from the structural instability due to the enhanced coupling between interlayer Pd and S atoms upon compression.

Superconductivity above 70 K observed in lutetium polyhydrides

The binary polyhydrides of heavy rare earth lutetium that shares a similar valence electron configuration to lanthanum have been experimentally discovered to be superconductive. The lutetium polyhydrides were successfully synthesized at high pressure and high temperature conditions using a diamond anvil cell in combinations with the in-situ high pressure laser heating technique. The resistance measurements as a function of temperature were performed at the same pressure of synthesis in order to study the transitions of superconductivity (SC). The superconducting transition with a maximum onset temperature (Tc) 71 K was observed at pressure of 218 GPa in the experiments. The Tc decreased to 65 K when pressure was at 181 GPa. From the evolution of SC at applied magnetic fields, the upper critical field at zero temperature {\mu}0Hc2(0) was obtained to be ~36 Tesla. The in-situ high pressure X-ray diffraction experiments imply that the high Tc SC should arise from the Lu4H23 phase with Pm-3n symmetry that forms a new type of hydrogen cage framework different from those reported for previous light rare earth polyhydride superconductors.

Pressure induced isostructural phase transition with volume expansion in DyFeO3 orthoferrite

The orthorhombic O and O′ structure phases of ABO3-type perovskites possess the same symmetry and quite different physical properties. In this work, a pressure induced isostructural O′–O phase transition with volume expansion and less distortion in DyFeO3 orthoferrite was experimentally observed and studied by high-pressure x-ray diffraction and Raman spectroscopy measurements. Up to 35.2 GPa, DyFeO3 crystallizes in an orthorhombic Pbnm symmetry structure. With no change in the symmetry group, distinct O′-phase and O-phase were verified below 13.1 GPa and above 15.1 GPa, respectively. Meanwhile, the lattice becomes less distorted and metrically pseudo-cubic on the high-pressure side. The cell volume expands by a step in the intermediate pressure window accompanied by a decrease in spontaneous strain. It is suggested that FeO6 octahedra are more compressible than DyO12 sites under pressure. This work claimed the physical mechanism underlying phonon dynamics and variation of local structure symmetry of DyFeO3, which can be considered as the basic view for RFeO3 perovskites.

Synchrotron X-ray powder diffraction under high pressures up to 33 MPa for mechanoresponsive materials.

Equipment for synchrotron X-ray diffraction at high pressures up to 33 MPa with an accuracy of ±0.1 MPa using a liquid as a pressure-transmitting medium has been developed. This equipment enables atomic-scale observation of the structural change of mechanoresponsive materials under applied pressures. The validity of the equipment is demonstrated by observation of the pressure dependence of the lattice parameters of copper. The observed bulk modulus of copper was found to be 139 (13) GPa which is a good agreement with the literature value. The developed equipment was subsequently applied to a repeatable mechanoluminescence material, Li0.12Na0.88NbO3:Pr3+. The bulk modulus and compressibility along the a and c axes were determined as 79 (9) GPa, 0.0048 (6) GPa-1 and 0.0030 (9) GPa-1, respectively, for the R3c phase. The advance of high-pressure X-ray diffraction will play an important role in understanding mechanoresponsive materials towards their atomic-scale design.

Exploring the hardness and high-pressure behavior of osmium and ruthenium-doped rhenium diboride solid solutions

Rhenium diboride (ReB2) exhibits high differential strain due to its puckered boron sheets that impede shear deformation. Here, we demonstrate the use of solid solution formation to enhance the Vickers hardness and differential strain of ReB2. ReB2-structured solid solutions (Re0.98Os0.02B2 and Re0.98Ru0.02B2, noted as “ReOsB2” and “ReRuB2”) were synthesized via arc-melting from the pure elements. In-situ high-pressure radial x-ray diffraction was performed in the diamond anvil cell to study the incompressibility and lattice strain of ReOsB2 and ReRuB2 up to ∼56 GPa. Both solid solutions exhibit higher incompressibility and differential strain than pure ReB2. However, while all lattice planes are strengthened by doping osmium (Os) into the ReB2 structure, only the weakest ReB2 lattice plane is enhanced with ruthenium (Ru). These results are in agreement with the Vickers hardness measurements of the two systems, where higher hardness was observed in ReOsB2. The combination of high-pressure studies with experimentally observed hardness data provides lattice specific information about the strengthening mechanisms behind the intrinsic hardness enhancement of the ReB2 system.

High-Pressure Structural and Thermodynamic Properties of Cerium Orthosilicates (CeSiO4)

Pressure-induced phase transitions from the zircon structure-type (I41/amd) to the scheelite structure type (I41/a) are known for many ternary oxides systems (ABO4). In this work, we present the first high-pressure study on synthetic stetindite (CeSiO4) by a combination of in situ high-pressure synchrotron powder X-ray diffraction up to 36 GPa, implemented with and without dual sided laser heating, and in situ high-pressure Raman spectroscopy up to 43 GPa. Two phase transitions were identified: zircon to a high-pressure low-symmetry (HPLS) phase at 15 GPa and then to a scheelite at 18 GPa. The latter from HPLS scheelite phase was found irreversible; i.e., scheelite is fully quenchable at ambient conditions, as in other zircon-type phases. The bulk moduli (K0) of stetindite, HPLS, and high-pressure scheelite phases were determined, respectively, as 171(5), 105(4), and 221(40) GPa by fitting to a second-order Birch–Murnaghan equation of state. The pressure derivatives of vibrational modes and Grüneisen parameters of the zircon-structured polymorph are similar to those of other orthosilicate minerals. Due to the larger ionic radii of Ce4+, with respect to Zr4+, stetindite was found to possess a softer bulk modulus and undergo the phase transitions at a lower pressure than zircon (ZrSiO4), such observations are consistent with what were found in coffinite (USiO4).

Structural and Luminescence Properties of Cu(I)X-Quinoxaline under High Pressure (X = Br, I)

A study of high-pressure single-crystal X-ray diffraction and luminescence experiments together with ab initio simulations based on the density functional theory has been performed for two isomorphous copper(I) halide compounds with the empirical formula [C8H6Cu2X2N2] (X = Br, I) up to 4.62(4) and 7.00(4) GPa for X-ray diffraction and 6.3(4) and 11.6(4) GPa for luminescence, respectively. An exhaustive study of compressibility has been completed by means of determination of the isothermal equations of state and structural changes with pressure at room temperature, giving bulk moduli of K0 = 14.4(5) GPa and K′0 = 7.7(6) for the bromide compound and K0 = 13.0(2) GPa and K′0 = 7.4(2) for the iodide compound. Both cases exhibited a phase transition of second order around 3.3 GPa that was also detected in luminescence experiments under the same high-pressure conditions, wherein redshifts of the emission bands with increasing pressure were observed due to shortening of the Cu–Cu distances. Additionally, ab initio studies were carried out which confirmed the results obtained experimentally, although unfortunately, the phase transition was not predicted.

57Fe Mössbauer spectroscopy and high-pressure structural analysis for the mechanism of pressure-induced unique magnetic behaviour in (cation)[FeIIFeIII(dto)3] (cation = Ph4P and nPrPh3P; dto = 1,2-dithiooxalato).

A mixed-valence iron(II,III) coordination polymer, (Ph4P)[FeIIFeIII(dto)3] (2; Ph4P = tetraphenylphosphonium, dto = 1,2-dithiooxalato), exhibits a thermal hysteresis loop and a low temperature shift of the ferromagnetic phase transition temperature, with increasing pressure. The latter magnetic behaviour can also be observed in a novel compound (nPrPh3P)[FeIIFeIII(dto)3] (3; nPrPh3P = n-propyltriphenylphosphonium). To understand the structural information under pressure, we performed high-pressure powder X-ray diffraction, and the result suggests that there was no structural phase transition for either compound. Considering the 57Fe Mössbauer spectroscopy studies, both 2 and 3 may have a high transition entropy, and this finding is caused by pressure-induced unique magnetic behaviours.

Tuning the mechanical properties of dicyanamide-based molecular perovskites

By combining lattice dynamic calculations and high-pressure powder X-ray diffraction, the mechanical properties of a series of dicyanamide-based molecular perovskites are studied.

Study on pressure-induced isostructural phase transition and electrical transport properties of BiOBr.

In this work, we prepared a BiOBr powder sample by the coprecipitation method for in situ high-pressure AC impedance spectroscopy tests, in situ high-pressure Raman measurements and in situ high-pressure X-ray diffraction experiments to explore its structural properties and electrical transport processes under compression. Two pressure-driven isostructural phase transitions, T-T' and T'-T'' (T - tetragonal, T' - tetragonal 1 and T'' - tetragonal 2), were discovered at around 10.0 and 15.0 GPa, respectively. The pressure-induced changes in the crystal structure and electrical transport of BiOBr can provide a reference for explaining the mechanism of the isostructural phase transition of other similar compounds after compression.

High-Pressure X-ray Diffraction and DFT Studies on Spinel FeV2O4

We have studied the behaviour of the cubic spinel structure of FeV2O4 under high-pressure by means of powder X-ray diffraction measurements and density-functional theory calculations. The sample was characterized at ambient conditions by energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction experiments. One of the main findings of this work is that spinel FeV2O4 exhibits pressure-induced chemical decomposition into V2O3 and FeO around 12 GPa. Upon pressure release, the pressure-induced chemical decomposition appears to be partially reversible. Additionally, in combination with density-functional theory calculations, we have calculated the pressure dependence of the unit-cell volumes of both the spinel and orthorhombic FeV2O4 crystal structures, whose bulk moduli are B0 = 123(9) and 154(2) GPa, respectively, finding the spinel FeV2O4 to exhibit the lowest bulk modulus amongst the spinel oxides. From experimental results, the same information is herein obtained for the cubic structure only. The Raman modes and elastic constants of spinel FeV2O4 have also obtained the ambient conditions.

Direct Observation of the Pressure-Induced Structural Variation in Gold Nanoclusters and the Correlated Optical Response.

The ability to gradually modify the atomic structures of nanomaterials and directly identify such structural variation is important in nanoscience research. Here, we present the first example of a high-pressure single-crystal X-ray diffraction analysis of atomically precise metal nanoclusters. The pressure-dependent, subangstrom structural evolution of an ultrasmall gold nanoparticle, Au25S18, has been directly identified. We found that a 0.1 Å decrease of the Au-Au bond length could induce a blue-shift of 30 nm in the photoluminescence spectra of gold nanoclusters. From theoretical calculations, the origins of the blue-shift and enhanced photoluminescence under pressure are investigated, which are ascribed to molecular orbital symmetry and conformational locking, respectively. The combination of the high-pressure in situ X-ray results with both theoretical and experimental optical spectra provides a direct and generalizable avenue to unveil the underlying structure-property relations for nanoclusters and nanoparticles which cannot be obtained through traditional physical chemistry measurements.

Influence of pressure-induced formation of dihydrogen bonds on lattice parameters, volume, and vibrational modes of ammonia borane.

The high-pressure phase of ammonia borane (NH3BH3) observed at ∼1.2GPa has been reported to result in pressure-induced formation of dihydrogen bonds at ∼4GPa. In this study, we performed high-pressure x-ray diffraction measurements on the high-pressure phase (up to ∼10.2GPa) using a He hydrostatic pressure medium to examine the influence of the formation of dihydrogen bonds on the lattice parameters and unit cell volume of NH3BH3. We observed a unique behavior in the pressure dependence of lattice parameters close to the pressure at which the dihydrogen bond was formed. The lattice parameters demonstrated hysteresis curves under compression and decompression conditions but the unit cell volume did not. Moreover, the pressure dependence of the unit cell volume could not be expressed using a single Birch-Murnaghan equation within an acceptable margin of error, thus suggesting a change in bulk modulus under compression. These results are considered to have originated from the pressure-induced formation of dihydrogen bonds. Moreover, high-pressure Raman scattering measurements and a simulation using density functional theory calculations revealed the vibrational modes of the high-pressure phase of NH3BH3. The results demonstrated that librational modes were enhanced by forming dihydrogen bonds. Moreover, the intramolecular stretching modes of BN, BH, and NH monotonically shifted with pressure, while the symmetrical in-plane bending modes of BH3 and NH3 split irrespective of the formation of dihydrogen bonds.

Tracking structural phase transitions via single crystal x-ray diffraction at extreme conditions: advantages of extremely brilliant source

Highly brilliant synchrotron source is indispensable to track pressure-induced phenomena in confined crystalline samples in megabar range. In this article, a number of experimental variables affecting the quality high-pressure single-crystal x-ray diffraction data is discussed. An overview of the recent advancements in x-ray diffraction techniques at extreme conditions, in the frame of European Synchrotron Radiation Facility (ESRF)- Extremely Bright Source (EBS), is presented. Particularly, ID15b and ID27 beamlines have profited from the source upgrade, allowing for measurements of a few-micron crystals in megabar range. In case of ID27, a whole new beamline has been devised, including installation of double-multilayer mirrors and double crystal monochromator and construction of custom-made experimental stations. Two case studies from ID27 and ID15b are presented. Hypervalent CsI3 crystals, studied up to 24 GPa, have shown a series of phase transitions: Pnma → P-3c1→ Pm-3 n. First transition leads to formation of orthogonal linear iodine chains made of I3 -. Transformation to the cubic phase at around 21.7 GPa leads to equalization of interatomic I–I distances and formation of homoleptic In m- chains. The second study investigates elastic properties and structure of jadarite, which undergoes isosymmetric phase transition around 16.6 GPa. Despite a few-micron crystal size, twinning and dramatic loss of crystal quality, associated with pressure-induced phase transitions, crystal structures of both compounds have been determined in a straightforward matter, thanks to the recent developments within ESRF-EBS.

Stabilization mechanism of molecular orbital crystals in IrTe2

Doped IrTe2 is considered a platform for topological superconductivity and therefore receives currently a lot of interest. In addition, the superconductivity in these materials exists in close vicinity to electronic order and the formation of molecular orbital crystals, which we explore here by means of high-pressure single crystal x-ray diffraction in combination with density functional theory. Our crystallographic refinements provide detailed information about the structural evolution as a function of applied pressure up to 42 GPa. Using this structural information for density functional theory calculations, we show that the local multicenter bonding in IrTe2 is driven by changes in the Ir-Te-Ir bond angle. When the electronic order sets in, this bond angle decreases drastically, leading to a stabilization of a multicenter molecular orbital bond. This unusual local mechanism of bond formation in an itinerant material provides a natural explanation for the different electronic orders in IrTe2. It further illustrates the strong coupling of the electrons with the lattice and is most likely relevant for the superconductivity in this material.

Interlayer Cation Polarizability Affects Supercritical Carbon Dioxide Adsorption by Swelling Clays.

Several strategies for mitigating the build-up of atmospheric carbon dioxide (CO2) bring wet supercritical CO2 (scCO2) in contact with phyllosilicates such as illites and smectites. While some work has examined the role of the charge-balancing cation and smectite framework features on CO2/smectite interactions, to our knowledge no one has examined how the polarizability of the charge-balancing cation influences these behaviors. In this paper, the scCO2 adsorption properties of Pb2+, Rb+, and NH4+ saturated smectite clays at variable relative humidity are studied by integrating in situ high-pressure X-ray diffraction (XRD), infrared spectroscopic titrations, and magic angle spinning nuclear magnetic resonance (MAS NMR) methods. The results are combined with previously published data for Na+, Cs+, and Ca2+ saturated versions of the same smectites to isolate the roles of the charge-balancing cations and perform two independent tests of the role of charge-balancing cation polarizability in determining the interlayer fluid properties and smectite expansion. Independent correlations developed for (i) San Bernardino hectorite (SHCa-1) and (ii) Wyoming montmorillonite (SWy-2) both show that cation polarizability is important in predicting the interlayer composition (mol% CO2 in the interlayer fluid and CO2/cation ratio in interlayer) and the expansion behavior for smectites in contact with wet and dry scCO2. In particular, this study shows that the charge-balancing cation polarizability is the most important cation-associated parameter in determining the expansion of the trioctahedral smectite, hectorite, when in contact with dry scCO2. While both independent tests show that cation polarizability is an important factor in smectite-scCO2 systems, the correlations for hectorite are different from those determined for montmorillonite. The root of these differences is likely associated with the roles of the smectite framework on adsorption, warranting follow-up studies with a larger number of unique smectite frameworks. Overall, the results show that the polarizability of the charge-balancing cation should be considered when preparing smectite clays (or industrial processes involving smectites) to capture CO2 and in predicting the behavior of caprocks over time.

Determination of P–V equation of state of a natural clinoptilolite using high-pressure powder synchrotron X-ray diffraction

Determination of P–V equation of state of a natural clinoptilolite using high-pressure powder synchrotron X-ray diffraction

Mechanical Properties of a New Hybrid Inorganic–Organic Framework: A Nanoindentation, High-Pressure X-ray Diffraction, and Computational Study

Mechanical Properties of a New Hybrid Inorganic–Organic Framework: A Nanoindentation, High-Pressure X-ray Diffraction, and Computational Study

Strain-induced structural and electronic phase transitions in ZrSe2: high pressure X-ray diffraction and Raman studies

Strain-induced structural and electronic phase transitions in ZrSe2: high pressure X-ray diffraction and Raman studies