Angle-dispersive X-ray Diffraction Research Articles

Hematite-goethite ratios at pH 2–13 and 25–170 °C: A time-resolved synchrotron X-ray diffraction study

Iron (oxyhydr)oxides are sensitive indicators of pH, Eh, temperature, microbial activity, and climate conditions in the Critical Zone. The most ubiquitous and environmentally significant iron oxides in most soils are two-line ferrihydrite, goethite, and hematite. Here we present a comprehensive study of the transformation of two-line ferrihydrite to hematite and goethite over a wide range of temperature (25–170 °C) and initial pH (2−13) conditions through ex situ batch and in situ synchrotron X-ray diffraction (XRD) experiments.Within the high time resolution of our experiments, goethite and hematite nucleated nearly simultaneously from ferrihydrite in nearly equal concentrations by mass. Hematite increased in abundance relative to goethite until a steady-state ratio was achieved, and both phases ceased growth on the depletion of ferrihydrite. Higher temperatures and lower water activities favored hematite formation at all pH values studied. In both our batch and our time-resolved, angle-dispersive synchrotron X-ray diffraction experiments, hematite was favored relative to goethite at an initial pH of 3 to 5. In contrast, goethite preferentially formed in neutral (initial pH 7–8) and highly alkaline conditions (initial pH ≥ 11). Surprisingly, mildly alkaline conditions (initial pH 9–11) induced the precipitation of a highly Fe-deficient (Feocc = ~0.80–0.90) variety of hematite known as “hydrohematite” in greater concentrations than goethite. Our results are useful for the application of hematite-goethite ratios as paleoclimate proxies for soil and sediment systems with low pH buffering capacities.

Structural evolution and bandgap modulation of layered β-GeSe2 single crystal under high pressure

Germanium diselenide (GeSe2) is a promising candidate for electronic devices because of its unique crystal structure and optoelectronic properties. However, the evolution of lattice and electronic structure of β-GeSe2 at high pressure is still uncertain. Here we prepared high-quality β-GeSe2 single crystals by chemical vapor transfer (CVT) technique and performed systematic experimental studies on the evolution of lattice structure and bandgap of β-GeSe2 under pressure. High-precision high-pressure ultra low frequency (ULF) Raman scattering and synchrotron angle-dispersive x-ray diffraction (ADXRD) measurements support that no structural phase transition exists under high pressure up to 13.80 GPa, but the structure of β-GeSe2 turns into a disordered state near 6.91 GPa and gradually becomes amorphous forming an irreversibly amorphous crystal at 13.80 GPa. Two Raman modes keep softening abnormally upon pressure. The bandgap of β-GeSe2 reduced linearly from 2.59 eV to 1.65 eV under pressure with a detectable narrowing of 36.5%, and the sample under pressure performs the piezochromism phenomenon. The bandgap after decompression is smaller than that in the atmospheric pressure environment, which is caused by incomplete recrystallization. These results enrich the insight into the structural and optical properties of β-GeSe2 and demonstrate the potential of pressure in modulating the material properties of two-dimensional (2D) Ge-based binary material.

Utilization of Fe2O3 Nanoparticles Synthesized by Novel ASH Supported Method in Arsenic Adsorption from the Contaminated Water

AbstractIron oxide (Fe2O3) nanoparticles are synthesized by novel, swift, extremely simple, requiring enormously less preparation time, and a financially savvy process called an ASH Supported method and utilized for expelling arsenic from water. A simulated sample of arsenic(III) of known concentration is prepared in the laboratory. This simulated sample of arsenic is treated with two different concentrations and phases of iron oxide nanoparticles for two different reaction times (1 and 24 h). Fe2O3 nanoparticles are observed in two phases, namely mixed and pure phase, in nanosized range confirmed by angle dispersive X‐ray diffraction (ADXRD). These nanoparticles are found to have 99% sorption efficiency and the highest adsorption capacity of 964 mg g−1 for arsenic(III) than reported earlier in any literature. The results show that 0.1 mg of Fe2O3 nanoparticles effectively remove arsenic(III) from the simulated water sample for 1 h reaction time. The maximum adsorption is obtained at a 7.0 pH value for minimal ionic strength. This article also renders that the arsenic removal is phase induced rather than size induced. Arsenic(III) removal by iron oxide nanoparticles synthesized by the above‐mentioned method is reported for the first time and this is the main attraction of the present work.

Evaluation of extremely steep residual stress gradients based on a combined approach using laboratory-scale equipment.

Surface treatments characterized by rapid heating and cooling (e.g. laser hardening) can induce very steep residual stress gradients in the direct vicinity of the area being treated. These gradients cannot be characterized with sufficient accuracy by means of the classical sin2Ψ approach applying angle-dispersive X-ray diffraction. This can be mainly attributed to limitations of the material removal method. In order to resolve residual stress gradients in these regions without affecting the residual stress equilibrium, another angle-dispersive approach, i.e. the universal plot method, can be used. A novel combination of the two approaches (sin2Ψ and universal plot) is introduced in the present work. Prevailing limits with respect to profiles as a function of depth can be overcome and, thus, high-resolution surface layer characterization is enabled. The data obtained are discussed comprehensively in comparison with results elaborated by energy-dispersive X-ray diffraction measurements.

Tuning the onset pressure of pressure-induced phase transition in indium phosphide by extrinsic doping

In-situ angle-dispersive X-ray diffraction (ADXRD) and Raman scattering were carried out to delineate the phase transitions under pressure in p-type zinc-doped indium phosphide (InP:Zn) at ambient temperature. The ADXRD measurements with pressure up to 17.3(2) GPa reveal that InP:Zn transforms from zinc-blende (ZB) to rock-salt (RS) structure in a pressure range of 8.1(2) - 8.6(1) GPa. The Raman scattering measurements indicate that the phase transition proceeds continuously over a wide range of pressure and reaches completion at the highest pressure applied (14.5(2) GPa) with significant metallization, as suggested by the disappearance of the transverse optical (TO) and longitudinal optical (LO) modes. In contrast, originally absent at ambient pressure, additional Raman shift of Zn local vibrational modes (LVMs), appeared at 276 cm-1 and 420.7(1) cm-1 within the pressure range of 2.2(1) up to 10.1(2) GPa, which can be attributed to Zn3P2 and VPZnInVP LO modes, respectively. The zero-pressure isothermal bulk moduli and its first order pressure derivatives for the zinc-blende InP:Zn are 79.44(2) GPa and 3.92(1), respectively. A total enthalpy change of about 45.45 KJ•mole-1 was derived for the ZB to RS structure transformation occurring at the pressure of 8.6(1) GPa. The present results suggest that diffusion of Zn in InP:Zn may have been governed by the modified substitution and interstitial (S–I) mechanism. Moreover, comparisons on the pressure-dependent behaviors in InP:Zn, InP:S, and InP:Fe extrinsically doped systems revealed that the exact type of the defects introduced into the lattice upon doping may have played crucial roles in the pressure-induced phase transitions.

Theoretical and experimental studies of compression and shear deformation behavior of Osmium to 280 GPa

The compression behavior of osmium metal was investigated up to 280 GPa (volume compression V/Vo = 0.725) under nonhydrostatic conditions at ambient temperature using angle dispersive axial x-ray diffraction (A-XRD) with a diamond anvil cell (DAC). In addition, shear strength of osmium was measured to 170 GPa using radial x-ray diffraction (R-XRD) technique in DAC. Both diffraction techniques in DAC employed platinum as an internal pressure standard. Density functional theory (DFT) calculations were also performed, and the computed lattice parameters and volumes under compression are in good agreement with the experiments. DFT predicts a monotonous increase in axial ratio (c/a) with pressure and the structural anomalies of less than 1% in (c/a) ratio reported below 150 GPa were not reproduced in theoretical calculations and hydrostatic measurements. The measured value of shear strength of osmium () approaches a limiting value of 6 GPa above a pressure of 50 GPa in contrast to theoretical predictions of 24 GPa and is likely due to imperfections in polycrystalline samples. DFT calculations also enable the studies of shear and tensile deformations. The theoretical ideal shear stress is found along the (001)[1–10] shear direction with the maximal shear stress ∼24 GPa at critical strain ∼0.13.

High-Pressure Studies of Trimethylsilane Azide by Raman Scattering and Synchrotron X-ray Diffraction.

We have reported the high-pressure behavior of energetic material trimethylsilane azide ((CH3)3SiN3, TMSiN3) by in situ Raman scattering and synchrotron angle-dispersive X-ray diffraction (ADXRD) measurements in diamond anvil cells with a pressure up to ∼40 GPa at ambient temperature. The analyses of Raman spectra showed two liquid-liquid phase transitions at 0.13 and 7.9 GPa. The XRD results verified that TMSiN3 remained in a liquid state throughout the phase transitions. In the pressure range of 0.13-2.6 GPa, the distortion of the Si-C3 bond and the shortening of the bond between azide group and silicon atom lead to the first phase transition. The second transition is ascribed to the rotation of methyl group at 7.9 GPa. With further compression, the azide groups become increasingly asymmetric, and completely amorphous at 33.8 GPa. This paper is useful to understand the behavior of azide group and the molecular structural evolution of organic azide under high pressure. The unique high-pressure behavior of the azide group in TMSiN3 may be useful for improving in the formation of the polynitrogen compound with azides.

Pressure induced structural phase crossover of a GaSe epilayer grown under screw dislocation driven mode and its phase recovery

Hydrostatically pressurized studies using diamond anvil cells on the structural phase transition of the free-standing screw-dislocation-driven (SDD) GaSe thin film synthesized by molecular beam epitaxy have been demonstrated via in-situ angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy. The early pressure-driven hexagonal-to-rock salt transition at approximately ~ 20 GPa as well as the outstandingly structural-phase memory after depressurization in the SDD-GaSe film was recognized, attributed to the screw dislocation-assisted mechanism. Note that, the reversible pressure-induced structural transition was not evidenced from the GaSe bulk, which has a layer-by-layer stacking structure. In addition, a remarkable 1.7 times higher in bulk modulus of the SDD-GaSe film in comparison to bulk counterpart was observed, which was mainly contributed by its four times higher in the incompressibility along c-axis. This is well-correlated to the slower shifting slopes of out-of-plane phonon-vibration modes in the SDD-GaSe film, especially at low-pressure range (< 5 GPa). As a final point, we recommend that the intense density of screw dislocation cores in the SDD-GaSe lattice structure plays a crucial role in these novel phenomena.

The role of intrinsic stacking fault in facilitating the pressure-induced phase transition in CoCrFeMnNi high entropy alloys

The pressure-induced phase transitions in CoCrFeNi and CoCrFeMnNi high entropy alloys (HEAs) at ambient temperature at pressure up to 24.0(2) and 19.4(2) GPa, respectively, were investigated using angle-dispersive X-ray diffraction (ADXRD). Structurally at ambient pressure, both CoCrFeNi and CoCrFeMnNi HEAs consist of face-centered cubic (fcc) structure with different lattice constants which are arisen primarily from the cellular growth of alloy during solidification. In-situ ADXRD measurements revealed no evidence of structural transformation in CoCrFeNi HEAs up to 24.0(2) GPa. The intrinsic stacking fault (ISF) begins to appear at 1.7(1) GPa and sustains up to 19.4(2) GPa. Moreover, an fcc to hexagonal close-packed (hcp) structural phase transition emerges at around 7.0(1) GPa in CoCrFeMnNi HEAs. The pressure dependent lattice constants and volume compression yield the zero-pressure isothermal bulk moduli of 187(4) GPa while the normalized c/a ratio 1.636(1) for the resultant hcp phase. The quantitative correlation of the ISF diffraction intensity shows that the appearance of ISF disrupts the crystal lattice to trigger, at around 7.0(1) GPa, fcc-to-hcp phase transition which persists sluggishly to the highest experiment pressure. Neutron powder diffraction (NPD) at pressure up to 8.9(2) GPa was performed in CoCrFeMnNi HEAs at ambient temperature to clarify the significance of pressure induced suppression of local magnetic moment on destabilization of the initial fcc structure. The results, however, suggest that the magnetism may only play a minor role, if not none, in facilitating the pressure-induced fcc-to-hcp phase transition in CoCrFeMnNi HEAs.

Hexagonal Si-Ge Class of Semiconducting Alloys Prepared by Using Pressure and Temperature.

Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500-1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery at ambient pressure of hexagonal Ge-Si solid solutions (P63 /mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be prepared for all Ge-Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge-Si solid solution family, and is of interest for optoelectronic applications.

Strength, deformation, and equation of state of tungsten carbide to 66 GPa

Strength, texture, and equation of state of hexagonal tungsten monocarbide (WC) have been determined under quasi-hydrostatic and non-hydrostatic compression to 66 GPa using angle-dispersive X-ray diffraction in the diamond anvil cell. Quasi-hydrostatic compression in a Ne pressure medium demonstrates that nanocrystalline WC is slightly less incompressible than bulk-scale WC, with respective bulk moduli of K0 = 377 ± 7 and 397 ± 7 GPa and pressure derivatives K0’ = 3.8 ± 0.3 and 3.7 ± 0.3. This decrease in incompressibility with grain size is similar to behavior observed in other ceramics. Under nonhydrostatic compression, WC supports a mean differential stress of ∼12-15 GPa at plastic yielding, which occurs at ∼30 GPa. Strength in WC is anisotropic, with the (001) plane supporting 29-42% higher stress than stresses calculated from mean strain. Simulations using an Elasto-ViscoPlastic Self-Consistent model indicate that strength inferred from lattice strain theory may be overestimated due to effects of plastic deformation. Plastic deformation generates a texture maximum near 〈2¯110〉 in the compression orientation, initially through prismatic slip on the {101¯0}〈1¯21¯0〉 and {101¯0}〈0001〉 slip systems, followed by activation of pyramidal slip on {101¯1}〈2¯113〉 at ∼40-50 GPa.

Elucidating the structural properties and reversible regional texture effect of GdB6 under high pressure

As hard and refractory materials with high chemical resistance and mechanical strength, lanthanide hexaborides (LnB6) have attracted much attention. Among the family of LnB6, gadolinium hexaboride (GdB6) occupies a special position due to the half-filled 4f shell of Gd. Here, using in situ synchrotron radiation angle-dispersive X-ray diffraction in a diamond anvil cell at room temperature, the structural stability and compression behavior of GdB6 are investigated extensively, GdB6 is observed to be structurally stable up to 73 GPa, and the bulk modulus of 177 GPa is obtained under hydrostatic compression. In this paper, an interesting observation of pressure-induced spotty diffraction rings of GdB6 is reported, its formation mechanism can be well described by the reversible regional texture effect, which highlights the rearrangement of crystal grains under high pressure. The rearrangement mechanism has been well explained by investigating the pressure dependence of full width at half maximum, macro-differential stress and grain size. Collective grain rotation behavior motivated by stress difference is critical for the rearrangement process, the strong isotropy and strong stability of GdB6 structure also provide necessary conditions for high-pressure grain rotation behavior. These results will help to promote the understanding of high-pressure structural properties of GdB6, and provide novel insights on the high-pressure grain behavior in hard materials with strong isotropy and three-dimensional skeleton constituted of strong covalent bonds.

High pressure structural evolution of cubic solid solution YbInO3

The structural evolution of cubic (c) solid solution YbInO3 (space group Ia3¯) under pressure has been investigated using synchrotron based angle dispersive x-ray diffraction measurements and density functional theory based first principles calculations. A first order irreversible structural phase transition is observed at ∼15 GPa. The ambient cubic phase coexists with the high pressure phase up to the highest pressure achieved in the experiment, i.e., 42 GPa. Based on experimental and theoretical investigations, the high pressure phase of c-YbInO3 is proposed to be an orthorhombic solid solution structure having the space group Pnma. In the high pressure Pnma phase, the coordination of Yb1/In1 (general site 4c) atoms with respect to O atoms increases from six to eight, while Yb2/In2 (special site 4b) atoms remain in six coordination. Our theoretical calculations show that distorted octahedra (YbO6 and InO6), sitting at the general position in c-YbInO3, change its geometry toward regular octahedra with increasing pressure, which gives rise to the phase transformation.

Pressure-induced structural transitions between successional superconducting phases in GeTe

Being a best-known prototype of phase-change materials, GeTe was reported to possess many high-pressure phases, whose structural evolution and superconductivity remain under debate for decades. Herein, we systematically investigated the pressure dependence of electrical transport and the structural evolution of the GeTe via in situ angle-dispersive synchrotron x-ray diffraction and resistance measurements up to 55 GPa. At room temperature, the structural phase transitions from the initial rhombohedral phase to the phase, and then to an orthorhombic Pnma phase, were observed at pressures of about 4 and 13.4 GPa, respectively. Furthermore, the metallization occurred at around 11 GPa, where the superconductivity could also be observed. With increasing pressure, the superconducting transition temperature increases monotonically from 5.7 to 6.4 K and then is independent of pressure above 23 GPa in the pure Pnma phase. These results provide insights into the pressure-dependent evolution of the structure and superconductivity in GeTe and have implications for the understanding of other IV–VI semiconductors at high pressure.

Pressure induced topological and structural transitions in iron and sulphur doped Sb2Te3

The high pressure study of topological materials under pressure is a puzzling but trending topic of investigation. Here, we report angle dispersive X-Ray diffraction (ADXRD) experiments of Sb1.9Fe0.1S0.15Te2.85. We have observed an electronic topological transition (ETT) along with three pressure-induced distinct structural phase transitions. The c/a anomaly provides the signature of ETT at ~2.5 GPa.

Elucidating the Phase Transformation and Metallization Behavior of Zinc Phosphide under High Pressure.

Among the family of II3V2-type compounds, zinc phosphide (Zn3P2) occupies a unique position. As one of the most promising semiconductors well-suited for photovoltaic applications, Zn3P2 has attracted considerable attention. The stability of its structure and properties are of great interest and importance for science and technology. Here, we systematically investigate the pressurized behavior of Zn3P2 using in situ synchrotron radiation angle-dispersive X-ray diffraction (ADXRD) and in situ electrical resistance measurement under high pressure. The ADXRD experiment shows that Zn3P2 undergoes an irreversible structural phase transition under high pressure, beginning at 11.0 GPa and being completed at ∼17.7 GPa. Consistently, the high-pressure electrical resistance measurement reveals a pressure-induced semiconductor-metal transition for Zn3P2 near 11.0 GPa. The kinetics of the phase transition is also studied using in situ electrical resistance measurement and can be well described by the classical Avrami model. What's more, the new high-pressure structure of Zn3P2 is refined to be orthorhombic with space group Pmmn; the lattice parameters and bulk modulus of this high-pressure phase are determined as a = 3.546 Å, b = 5.004 Å, c = 3.167 Å, and B0 = 126.3 GPa. Interestingly, we also predict a possible structural phase transformation of orthorhombic phase (Pmmn) to cubic phase (P4232) during the decompression process; this cubic Zn3P2 is metastable at ambient conditions. These experimental results reveal the unexpected high-pressure structural behaviors and electrical properties of Zn3P2, which could help to promote the further understanding and the future applications of Zn3P2 as well as other II3V2 compounds.

High pressure induced the polymorphism phase transition in the Fe40Mn40Co10Cr10 multi-principal element alloy

In this study, we systematically studied the high pressure polymorphism phase transition process in the Fe40Mn40Co10Cr10 multi-principal element alloy through the hexahedron pressure equipment and the high pressure synchrotron angle-dispersive x-ray diffraction technique. A mixture of face-center cubic (fcc) + hexagonal close packed (hcp) nanolaminate structure was observed for the samples after high pressure treatment at 5 GPa, through the hexahedron pressure equipment. Especially, the hcp lath interaction structure with a new secondary hcp phase at the intersection zone was discovered in the sample. Transmission Electron Microscopy (TEM) analysis revealed that the transition from fcc to hcp was accomplished by the glide of Shockley partial dislocations. In addition, the in-situ synchrotron angle-dispersive x-ray diffraction technique was carried out to detect the phase transition process of the Fe40Mn40Co10Cr10 alloy up to 40.4 GPa. The lattice constant, atomic volumes, bulk modulus, and volume fraction of the fcc and hcp phase were obtained during compression and decompression. These results can expand our understanding of the structure evolution and properties of multi-principal element alloys under extreme conditions such as high pressure, which is contribute to the development of new metastable structural materials.

The coupling of lattice-strain and phonon induced order-disorder phase transition in layered LiGaO2

Recently, order-disorder phase transition has been considered as an emerging method to engineer bandgap in semiconductors. In this work, we uncovered that the coupling of lattice strain and phonon dominates the pressure-induced order-disorder phase transition in α-LiGaO2 via in situ high-pressure angle dispersive X-ray diffraction (ADXRD) and Raman scattering experiments, with the aids of first-principles calculations. Upon compression, ADXRD experiments show that the anisotropic compression of the layered structure leads to the order-disorder phase transition. Combining with lattice dynamics, we observed that the transition begins at about 16 GPa based on coherent nucleation induced by the oxygen atoms opposite motion that is the result of the coupling of lattice strain and phonon mode A1g. This result further shows that the disorder in crystal can be a correlated behavior and controlling the disorder in crystal can be used to create materials with new or improved functionality.

Structural and electronic phase transition in Bi2Se2.1Te0.9 under pressure

The phase evolution of Bi2Se2.1Te0.9 driven by the applied external pressure at ambient temperature was investigated in-situ with pressure up to 30.0(2) GPa using angle-dispersive X-ray diffraction (ADXRD) and Raman scattering spectroscopy. ADXRD measurements revealed that starting from the ambient rhombohedral structure (phase I), new forms of crystal structures are found to sequentially emerge with increasing externally applied pressure. Namely a seven-fold monoclinic structure (phase II), then an eight-fold monoclinic structure (phase III), a body-centered structure (BCC, phase IV), and finally a body-centered tetragonal structure (BCT, phase V) was observed at pressures of ~10.5(3) GPa, ~18.8(1) GPa, ~23.0(1) GPa, and ~28.0(2) GPa, respectively. The Raman scattering spectroscopy consistently showed that the pressures at which the corresponding phase appeared at ~10.2(2) GPa, ~18.9(1) GPa, and ~26.1(2) GPa, respectively. Moreover, the rhombohedral phase exhibited an even more pronounced signature of electronic topological transition in low-pressure regime, as compared with those previously observed in pristine Bi2Te3 and Bi2Se3. It appears that the alloying of Bi2Se3 with Bi2Te3 has led to more profound effects in the electronic and structural properties of the resultant system than that expected from the Vegard's law.

Phase transformations of zircon-type DyVO4 at high pressures up to 36.4 GPa: X-ray diffraction measurements

The compression behavior of zircon-type DyVO4 has been investigated in a diamond anvil cell by angle-dispersive X-ray diffraction (ADXRD) at high pressures up to 36.4 GPa. Under quasi-hydrostatic compression with argon as the pressure transmitting medium, DyVO4 underwent a sluggish zircon-to-scheelite phase transformation that started at approximately 8.0 GPa and was completed at 15.3 ± 0.9 GPa. The scheelite-type phase remained stable at pressures up to 25.3 GPa and during the process of decompression to ambient conditions, implying that the zircon-to-scheelite transformation is irreversible. Fitting the pressure-volume data using the third-order Birch-Murnaghan equation of state yielded a bulk modulus B0 = 129 (7) GPa and a pressure derivative of bulk modulus B′ = 3.4 (4) for the zircon-type phase, and B0 = 184 (10) GPa and B′ = 5.3 (8) for the scheelite-type phase. When compressed in a methanol-ethanol (4:1) pressure transmitting medium, DyVO4 was transformed into the scheelite-type phase at a pressure of 8.8 ± 1.1 GPa and then transformed into a fergusonite-type phase at 21.3 ± 1.6 GPa. The scheelite-to-fergusonite transformation was reversible during decompression. Our study indicates that DyVO4 under compression experiences a sequential zircon-scheelite-fergusonite phase transformation and that the scheelite-fergusonite transformation is sensitive to nonhydrostatic conditions.