Angle-dispersive X-ray Diffraction Research Articles

Equation of state, phase transitions, and band-gap closure in PbCl2 and SnCl2

The equations of state and band-gap closures for $\mathrm{Pb}{\mathrm{Cl}}_{2}$ and $\mathrm{Sn}{\mathrm{Cl}}_{2}$ were studied using both experimental and theoretical methods. We measured the volume of both materials to a maximum pressure of 70 GPa using synchrotron-based angle-dispersive powder x-ray diffraction. The lattice parameters for both compounds showed anomalous changes between 16--32 GPa, providing evidence of a phase transition from the cotunnite structure to the related ${\mathrm{Co}}_{2}\mathrm{Si}$ structure, in contrast to the postcotunnite structure as previously suggested. First-principles calculations confirm this finding and predict a second phase transition to a ${\mathrm{Co}}_{2}\text{Si-like}$ structure between 75-- 110 GPa in $\mathrm{Pb}{\mathrm{Cl}}_{2}$ and 60--75 GPa in $\mathrm{Sn}{\mathrm{Cl}}_{2}$. Band gaps were measured under compression to \ensuremath{\sim}70 GPa for $\mathrm{Pb}{\mathrm{Cl}}_{2}$ and \ensuremath{\sim}66 GPa for $\mathrm{Sn}{\mathrm{Cl}}_{2}$ and calculated up to 200 GPa for $\mathrm{Pb}{\mathrm{Cl}}_{2}$ and 120 GPa for $\mathrm{Sn}{\mathrm{Cl}}_{2}$. We find an excellent agreement between our experimental and theoretical results when using the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional, which suggests that this functional could reliably be used to calculate the band gap of similar $A{X}_{2}$ compounds. Experimental and calculated band-gap results show discontinuous decreases in the band gap corresponding to phase changes to higher-coordinated crystal structures, giving insight into the relationship between interatomic geometry and metallicity.

The pressure-induced structural transformation of La2S3

As a fundamental thermodynamic parameter, pressure can cause matters to produce new phases with unique physical properties. In this paper, the pressure-induced behavior of La2S3 has been investigated in depth by in-situ high pressure synchrotron angle dispersive X-ray diffraction (ADXRD), and the pressure is up to 26 GPa. We find the conventional La2S3 which was stable at ambient pressure, was destabilized with the application of pressure and decomposed into La3S4 and LaS2 at 13.4 GPa. This is the first time that the high pressure decomposition of La2S3 has been found in the experiments. The La2S3 possesses the lowest formation enthalpy at atmospheric pressure, enthalpy change increases with the pressure increasing, leading to the decomposition of La2S3. The high pressure inhibits the ability of S atoms to accept electrons and promotes the polymerization of S atoms to form shared electron pairs, brings in the change of S–S bonding modes, and also further leads to the change of structural. The study of pressure relief experiment shows that the pressure induced decomposition in La2S3 is an irreversible phase transition. The different radial direction has the different compression effects under pressure, the initial structure decays rapidly driven by pressure. With the pressure rising, the decay rate becomes gentle. The volume expansion of La3S4 and LaS2 may be due to some defects, and the smaller the volume, the greater the bulk modulus. This work provides a strong support for the theoretical research results and is expected to provide guidance for the experiment study of the physical properties and structural characteristics of La–S system and other rare earth sulfur compounds.

Hybrid energy and angle dispersive X-ray diffraction computed tomography.

Pixelated energy resolving detectors enable acquisition of X-ray diffraction (XRD) signals using a hybrid energy- and angle- dispersive technique, potentially paving the way for the development of novel benchtop XRD imaging or computed tomography (XRDCT) systems, utilising readily available polychromatic X-ray sources. In this work, a commercially available pixelated cadmium telluride (CdTe) detector, HEXITEC (High Energy X-ray Imaging Technology), was used to demonstrate such an XRDCT system. Specifically, a novel fly-scan technique was developed and compared to the established step-scan technique, reducing the total scan time by 42% while improving the spatial resolution, material contrast and therefore the material classification.

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.

Effects of High Pressure on the Bandgap and the d–d Crystal Field Transitions in Wolframite NiWO4

The pressure effects on the optical and structural properties of NiWO4 have been studied experimentally and theoretically. The fundamental bandgap decreases with a pressure coefficient of −12.0 ± 0.2 meV/GPa. Meanwhile, the Ni2+ d–d transition energies increase at a rate of 7.4–14.8 meV/GPa. Therefore, the energy differences between the fundamental band and the Ni2+ d–d transition bands gradually decrease under pressure, which is beneficial to improve its optical performance. These optical phenomena are associated with structural variations. The shrinkage of the WO6 octahedron enhances the hybridization between the W 5d and O 2p orbitals, resulting in bandgap reduction. The pressure-induced enhancement of the NiO6 octahedral symmetry increases the crystal field splitting, thereby yielding increases in the Ni2+ d–d intraband transition energies. Besides, a pressure-induced structural phase transition is also observed around 20.0 GPa by both angle-dispersive synchrotron X-ray diffraction (ADXRD) and Raman experiments. This study provides valuable insight into the electron–lattice coupling of NiWO4 under compression and an effective way to modulate the electronic structure and optical properties of isomorphic wolframite materials.

Structural correlation to enhanced magnetodielectric properties of Pr-doped polycrystalline Gd0.55Pr0.45MnO3 at low temperatures

The effect of improved dielectric properties in the presence of an applied magnetic field is discussed in polycrystalline Gd0.55Pr0.45MnO3 complemented by the structural and magnetic properties. Enhanced dielectric permittivity and low dielectric loss represent the strongly field-dependent dielectric behaviour of the sample. The structural characterizations using synchrotron angle dispersive X-ray diffraction confirm the orthorhombic symmetry of the polycrystalline sample with the Pnma space group in the temperature range from 300 K to 50 K. There is no structural transition observed at lower temperatures down to 50 K; however the Mn- O octahedral distortion is slightly reduced. The magneto-dielectric measurements were performed in the frequency range 500 Hz–1 MHz and temperature range 8 K–300 K both with and without external magnetic field (up to 7 Tesla), which shows the high dielectric constant. The magnetic study shows the negative magnetization and high coercivity in Gd0.55Pr0.45MnO3 at low temperatures due to competition in between spin ordering of Mn and Gd + Pr magnetic lattice. The MnOMn bond angle study indicates the A-type antiferromagnetic structure of the material at lower temperature.

Equations of State and Crystal Structures of KCaPO4, KSrPO4, and K2Ce(PO4)2 under High Pressure: Discovery of a New Polymorph of KCaPO4.

We have studied by means of angle-dispersive powder synchrotron X-ray diffraction the structural behavior of KCaPO4, SrKPO4, and K2Ce(PO4)2 under high pressure up to 26, 25, and 22 GPa, respectively. For KCaPO4, we have also accurately determined the crystal structure under ambient conditions, which differs from the structure previously reported. Arguments supporting our structural determination will be discussed. We have found that KCaPO4 undergoes a reversible phase transition. The onset of the transition is at 5.6 GPa. It involves a symmetry decrease. The low-pressure phase is described by space group P3̅m1 and the high-pressure phase by space group Pnma. For KSrPO4 and K2Ce(PO4)2, no evidence of phase transitions has been found up to the highest pressure covered by the experiments. For the three compounds, the linear compressibility for the different crystallographic axes and the pressure-volume equation of states are reported and compared with those of other phosphates. The three studied compounds are among the most compressible phosphates. The results of the study improve the knowledge about the high-pressure behavior of complex phosphates.

X-ray diffraction line profile analysis of defects in neutron-irradiated austenitic stainless steels at low displacement damage levels

Neutron irradiation-induced microstructural changes in variants of austenitic stainless steels were characterized using the Angle Dispersive X-Ray Diffraction (ADXRD) technique with a synchrotron X-ray source of energy 14.968 keV (wavelength ∼0.82833 Å). SS 304 L(N), SS 316 L(N), and SS 316 materials were neutron-irradiated to low displacement damage levels (1–6.75 dpa) in the Fast Breeder Test Reactor at Kalpakkam at temperatures in the range ∼380 °C-400 °C. The effect of the irradiation-induced defects on X-ray diffraction peak profile parameters such as peak broadening, peak shift, and asymmetry were quantified and related to dislocation density. Peak broadening is found to increase as a function of dpa in most of the cases. Considering the highest dpa sample, lattice contraction has been shown by SS 304 L(N) and SS 316 whereas lattice expansion is exhibited by SS 316 L(N). Asymmetry in peak broadening is found to decrease in case of the highest dpa sample. Ferrite volume percent is seen to have increased as a function of dpa in SS 304 L(N) and SS 316 L(N) but not observed in SS 316. SS 304 L(N) has shown a greater propensity towards the austenite to ferrite transformation and 5 dpa sample has about 18 vol% of α-ferrite. However, in case of 5 dpa SS 316 L(N), ferrite content has increased to ∼4 vol% . The increase in yield strength was also related to the dislocation density amongst all three grades of stainless steel. SS 304 L(N) showed saturation in dislocation density and yield strength around 2 dpa whereas SS 316 L(N) showed linear behaviour up to the highest dpa.

Thermal expansion behavior of Li-bearing tourmalines investigated by high-temperature synchrotron-based X-ray diffraction

The high-temperature unit-cell parameters and volumes of three Li-bearing tourmalines (elbaite (CC05), elbaite (CC11) and schorl (D54)) have been determined through in situ synchrotron radiation angle-dispersive X-ray diffraction experiments. No phase transition of these tourmalines has been observed up to the maximum temperature in this study. The volumetric thermal expansion coefficients of the three Li-bearing tourmalines are determined from the measured unit-cell volumes at high temperatures with Berman's equations. And the elbaite (CC05) has the least volumetric thermal expansion coefficients among the three Li-bearing tourmalines in this study. Furthermore, the axial thermal expansion behavior of these Li-bearing tourmalines is also fitted with “linearized” Berman's equation. The results show that Li-bearing tourmalines has an intense anisotropic axial thermal expansivity, where the c-axis has a larger axial thermal expansion coefficient than a-axis. The potential factors influencing on the thermal expansivity and the anisotropic axial thermal expansivities of Li-bearing tourmalines are further discussed.

Experimental and theoretical revelation of a unique band topology in Sb[formula omitted]Te[formula omitted] topological insulator by substitution of Cu—A high pressure study

TI Sb1.9Cu0.1Te3 is an ideal platform for investigating such semiconducting to metal transition under extreme conditions. The unusual softening of two newly M1, M2 phonon modes combined with the sudden collapse in bond length, angle of succession, intralayer distance and the direct observation of band gap closure from theoretical density functional theory calculation validates a unique metal transition. To the best of our knowledge, the metallic transition pressure in the present observation is the lowest amongst the A2B3 TI family of compounds. This distinctive transition is stimulated by the p-d hybridization which is the concomitant effect of Cu and applied pressure. We also establish structural and vibrational anomalies from pressure induced angle dispersive synchrotron x-ray diffraction and Raman spectra of the bulk that signify changes in electronic topology of the Fermi surface. Our experimental observations on bulk corroborates an ETT (∼2.5 GPa) and 3 structural transitions in the present system.

An experimental investigation on the combined effect of plastic deformation and grain size variation on the acoustic nonlinearity parameter.

The combined effect of grain size variation and plastic deformation on the acoustic nonlinearity parameter has been investigated in an austenitic stainless-steel material of grade 304. The nonlinear behavior of this parameter with grain growth has deviated to linear fit with deformation. This is due to the interaction of elastic waves with the strain-induced dislocation substructure in the grains. The normalized mean square strain of the deformed specimens has been estimated through angle dispersive x-ray diffraction studies using a synchrotron source, and this has been correlated with the change in the acoustic non-linearity parameter with deformation. The nonlinearity parameter is found to be very sensitive to the plastic deformation even in the presence of grain size variations. The results infer that the variations in the nonlinearity parameter can be used to have an estimate of the extent of localized deformations often occurring during the fabrication of metallic components.

Pair distribution function analysis on nanocrystalline semiconductors ZnS and CdS

Nanosized Zinc sulfide (ZnS) and Cadmium sulfide (CdS) are essential materials for various applications, and understanding their atomic arrangement is critical for enhancing their performance. ZnS and CdS nanoparticles were synthesized via the chemical co-precipitation method using methacrylic acid as a surfactant. Angle dispersive x-ray diffraction (ADXRD), and pair distribution function (PDF) were utilized to evaluate structural parameters and atomic structures, respectively. It was confirmed that both samples have a Zink Blend structure. Optical properties and band gaps were estimated using UV–vis spectra. The PDF analysis provided detailed information on the Bravais lattices, lattice parameters, cation-cation, and cation–anion distances in ZnS and CdS. Our results show that methacrylic acid is an effective surfactant for synthesizing high-quality ZnS and CdS nanoparticles with well-defined atomic structures. Specifically, the cation–anion distance for Zn-S was found to be 0.2326 nm, and the cation-cation distance for Zn-Zn was 0.3798 nm, while the cation–anion distances for Cd-S and Cd-Cd were found to be 0.251 nm and 0.41 nm, respectively. Overall, our study demonstrates the effectiveness of PDF analysis in investigating the atomic structure of nanomaterials, and these findings could have important implications for the development of advanced nanomaterials for various applications.[copyright information to be updated in production process]

Engineering ZnO with Cu doping to lower the transition pressure: Experimental and theoretical investigations

Zinc Oxide (ZnO) is an n-type wide bandgap semiconductor. Doping of different elements in ZnO potentially affects its structural, optical and electronic properties. We have carried out high pressure angle dispersive x-ray diffraction and Raman scattering studies on Zn0.99Cu0.01O. We observed the substantial lowering of the transition pressure threshold from the wurtzite to rock salt phase compared to pristine ZnO. Experimental findings are also supported through computational data from density functional theory simulations. The charge transfer from a Cu atom in ZnO may be responsible for the reduction in the transition pressure threshold.

Raman and synchrotron X‐ray diffraction studies of 4‐azidobenzoic acid under high pressures

AbstractHere, we report the distinct behaviors of 4‐azidobenzoic acid (C7H5N3O2, 4‐ABA) in diamond anvil cells with the pressure up to ∼18 GPa at room temperature by in situ Raman scattering and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) measurements. The analyses of Raman spectra revealed that 4‐ABA underwent a phase transition in the pressure range of 0.8–1.3 GPa and a conformational change at 6.3 GPa, which were supported by XRD results. The phase transition is attributed to the distortion of the benzene ring, and the change of hydrogen bonds results in the conformational change. Above 11.2 GPa, the (112) Bragg peak moved toward a low angle, indicating the increase of the interplanar distance of 4‐ABA. Upon compression to 18.0 GPa, 4‐ABA transformed into amorphous phase that the low amorphization pressure is helpful for nitrogen polymerization. This study provides an effective route for understanding the evolution of the azide group under high pressure, which is beneficial to studying the mechanism of forming polymeric nitrogen.

Synthesis and Ultrahigh Pressure Compression of High-Entropy Boride (Hf0.2Mo0.2Nb0.2Ta0.2Zr0.2)B2 to 220 GPa.

The high-entropy boride (Hf0.2Mo0.2Nb0.2Ta0.2Zr0.2)B2 material was synthesized under high-pressures and high-temperatures in a large-volume Paris-Edinburgh (PE) press from a ball-milled powder mix of HfO2, MoO3, Nb2O5, Ta2O5, ZrO2, carbon black, and boron carbide. The transformation process was monitored in situ by energy-dispersive x-ray diffraction with conversion starting at 1100 °C and completed by 2000 °C with the formation of a single hexagonal AlB2-type phase. The synthesized sample was recovered, powdered, and mixed with platinum pressure marker and studied under high pressure by angle-dispersive x-ray diffraction in a diamond anvil cell. The hexagonal AlB2-type phase of (Hf0.2Mo0.2Nb0.2Ta0.2Zr0.2)B2 was found to be stable up to the highest pressure of 220 GPa reached in this study (volume compression V/V0 = 0.70). The third order Birch-Murnaghan equation of state fit to the high-pressure data up to 220 GPa results in an ambient pressure unit cell volume V0=28.16±0.04 Å3, bulk modulusKo = 407 ± 6 GPa, pressure derivative of bulk-modulus K0′ = 2.73 ± 0.045 GPa. Our study indicates that this high-entropy boride (Hf0.2Mo0.2Nb0.2Ta0.2Zr0.2)B2 material is stable to ultrahigh pressures and temperatures and exhibit high bulk modulus similar to other incompressible transition metal borides like ReB2 and Os2B3.

Vacancy infilling during the crystallization of Fe-deficient hematite: An in situ synchrotron X-ray diffraction study of non-classical crystal growth

Abstract The crystallization of hematite from precursor ferrihydrite was studied using time-resolved, angle-dispersive synchrotron X-ray diffraction in aqueous solutions at pH 10 and 11 and at temperatures ranging from 80 to 170 °C. Rietveld analyses revealed a non-classical crystallization pathway involving vacancy infilling by Fe as defective hematite nanocrystals evolved. At 90 °C and pH 11, incipient hematite particles exhibited an Fe site occupancy as low as 0.68(2), and after 30 min, Fe occupancy plateaued at 0.84(1), achieving a metastable steady state with a composition corresponding to “hydrohematite.” During crystal growth, unit-cell volume increased with an increase in Fe occupancy. The increase in Fe occupancy in hydrohematite was accomplished by deprotonation, resulting in a shortening of the long Fe-O(H) bonds and decreased distortion of the octahedral sites. Once the occupancy stabilized, the unit-cell volume contracted following further nanoparticle growth. Our study documented various synthetic routes to the formation of “hydrohematite” with an Fe vacancy of 10–20 mol% in the final product. The structure refined for synthetic hydrohematite at 90 °C and pH 11 closely matched that of natural hydrohematite from Salisbury, Connecticut, with a refined Fe occupancy of 0.83(2). Dry heating this natural hydrohematite generated anhydrous, stoichiometric hematite, again by continuous infilling of vacancies. The transformation initiated at 150 °C and was complete at 700 °C, and it was accompanied by the formation of a minor amorphous phase that served as a reservoir for Fe during the inoculation of the defective crystalline phase.

Yield strength of CeO2 measured from static compression in a radial diamond anvil cell

Cerium oxide (ceria, CeO2) is frequently used as a standard in applications such as synchrotron and x-ray free electron lasers for calibrating x-ray wavelengths and offers the potential for understanding the high pressure properties and deformation mechanisms in a wide range of similar face centered cubic (fcc) materials. In this study, the pressure dependence of the strength of ceria was investigated up to 38 GPa using angle dispersive x-ray diffraction in a radial geometry in a diamond anvil cell. In this experiment, the difference in the stress along the axis of compression and perpendicular to the direction of compression can be determined, giving a quantity known as the differential stress. It was found that the differential stress (t), a measure of the lower bound for yield strength, initially increases rapidly from 0.35 ± 0.06 GPa to 2.2 ± 0.4 GPa at pressures of 1.8 and 3.8 GPa, respectively. Above 4 GPa, t increases more slowly to 13.8 ± 2.6 GPa at a pressure of 38 GPa. The changes in the preferred orientation (texture) of CeO2 with pressure were also measured, allowing for the determination of active deformation mechanisms using an elasto-viscoplastic self-consistent model (EVPSC). It was found that as pressure increased, the [001] direction had a slight preferred orientation along the axis of compression. Our EVPSC model of experimental fiber (cylindrically symmetric) textures and lattice strains were most consistent with dominant slip activity along {111}⟨11¯0⟩.

Fluorescence-based monitoring of the pressure-induced aggregation microenvironment evolution for an AIEgen under multiple excitation channels

The development of organic solid-state luminescent materials, especially those sensitive to aggregation microenvironment, is critical for their applications in devices such as pressure-sensitive elements, sensors, and photoelectric devices. However, it still faces certain challenges and a deep understanding of the corresponding internal mechanisms is required. Here, we put forward an unconventional strategy to explore the pressure-induced evolution of the aggregation microenvironment, involving changes in molecular conformation, stacking mode, and intermolecular interaction, by monitoring the emission under multiple excitation channels based on a luminogen with aggregation-induced emission characteristics of di(p-methoxylphenyl)dibenzofulvene. Under three excitation wavelengths, the distinct emission behaviors have been interestingly observed to reveal the pressure-induced structural evolution, well consistent with the results from ultraviolet-visible absorption, high-pressure angle-dispersive X-ray diffraction, and infrared studies, which have rarely been reported before. This finding provides important insights into the design of organic solid luminescent materials and greatly promotes the development of stimulus-responsive luminescent materials.

Raman spectroscopy and X‐ray diffraction of diphenylphosphoryl azide under high pressures

AbstractDiphenylphosphoryl azide ((C6H5O)2P(O)N3, DPPA) was studied by in situ Raman scattering spectroscopy and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) technologies up to 11.6 GPa at room temperature. The analyses of Raman spectra revealed that the liquid DPPA transformed from Phase I to Phase II at 0.4 GPa and went to Phase III at 1.3 GPa. The first phase transition was attributed to the change of molecular conformation, and the second phase transition was induced by the deformation of benzene rings. The XRD results suggested that DPPA remained in a liquid state during the two phase transitions. The azide group became increasingly asymmetric under pressure and decomposed at 11.6 GPa. The low decomposition pressure of the azide group is conducive to the formation of polymeric nitrogen. Exploring the behaviors of the azide group under pressure might be helpful for understanding the potential application of DPPA in the synthesis of high energy density materials (HEDMs).

Thermal expansion and compressibility of calcium scandate CaSc2O4

By using in-situ synchrotron angle-dispersive X-ray diffraction measurements, the thermal expansion and compressibility of orthorhombic CaSc2O4 were investigated up to 1173 K at ambient pressure and up to 15.9 GPa at room temperature, respectively. No phase transformation was observed in this study. The thermal expansion coefficients of CaSc2O4 were determined to be 4.17(3) × 10−5 K−1, 1.60(1) × 10−5 K−1, 1.18(1) × 10−5 K−1 and 1.39(1) × 10−5 K−1 for the V, a-, b- and c-axis, respectively. The isothermal bulk modulus of CaSc2O4 was obtained as 153.8(50) GPa with its first pressure derivative of 6.5(9). The axial compressibility was estimated to be 123(3), 177(4) and 242(11) GPa for the a-, b- and c-axis, respectively. Both the thermal expansion and compressibility of CaSc2O4 show axial anisotropy. The heat capacities (Cv and Cp) of CaSc2O4 was estimated by using a Kieffer model with Raman spectroscopy data and present experimental results. The standard entropy (S2980) and Debye temperature (θD) of CaSc2O4 were also calculated.