Angle-dispersive Synchrotron X-ray Diffraction Research Articles

Evidence of polymorphic transformations of Sn under high pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 11304294 and 11274281) and the Science Fund from the National Laboratory of Shock Wave and Detonation Physics of China (Grant Nos. 9140C670201140C67281 and 9140C670102150C67288).

The high-pressure polymorphs and structural transformation of Sn were experimentally investigated using angle-dispersive synchrotron x-ray diffraction up to 108.9 GPa. The results show that at least at 12.8 GPa β-Sn→bct structure transformation was completed and no two-phase coexistence was found. By using a long-wavelength x-ray, we resolved the diffraction peaks splitting and discovered the formation of a new distorted orthorhombic structure bco from the bct structure at 31.8 GPa. The variation of the lattice parameters and their ratios with pressure further validate the observation of the bco polymorph. The bcc structure appears at 40.9 GPa and coexists with the bco phase throughout a wide pressure range of 40.9 GPa–73.1 GPa. Above 73.1 GPa, only the bcc polymorph is observed. The systematically experimental investigation confirms the phase transition sequence of Sn as β-Sn→bct→bco→bco+bcc→bcc upon compression to 108.9 GPa at room temperature.

Polymorphism in Strontium Tungstate SrWO4 under Quasi-Hydrostatic Compression.

The structural and vibrational properties of SrWO4 have been studied experimentally up to 27 and 46 GPa, respectively, by angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy measurements as well as using ab initio calculations. The existence of four polymorphs upon quasi-hydrostatic compression is reported. The three phase transitions were found at 11.5, 19.0, and 39.5 GPa. The ambient-pressure SrWO4 tetragonal scheelite-type structure (S.G. I41/a) undergoes a transition to a monoclinic fergusonite-type structure (S.G. I2/a) at 11.5 GPa with a 1.5% volume decrease. Subsequently, at 19.0 GPa, another structural transformation takes place. Our calculations indicate two possible post-fergusonite phases, one monoclinic and the other orthorhombic. In the diffraction experiments, we observed the theoretically predicted monoclinic LaTaO4-type phase coexisting with the fergusonite-type phase up to 27 GPa. The coexistence of the two phases and the large volume collapse at the transition confirm a kinetic hindrance typical of first-order phase transitions. Significant changes in Raman spectra suggest a third pressure-induced transition at 39.5 GPa. The conclusions extracted from the experiments are complemented and supported by ab initio calculations. Our data provides insight into the structural mechanism of the first transition, with the formation of two additional W-O contacts. The fergusonite-type phase can be therefore considered as a structural bridge between the scheelite structure, composed of [WO4] tetrahedra, and the new higher pressure phases, which contain [WO6] octahedra. All the observed phases are compatible with the high-pressure structural systematics predicted for ABO4 compounds using crystal-chemistry arguments such as the diagram proposed by Bastide.

Pressure-induced transition to Ni2In-type phase in lithium sulfide (Li2S)

Raman spectroscopy and synchrotron angle-dispersive X-ray diffraction were applied to investigate pressure-induced phase transitions in lithium sulfide (Li2S). We observed two reversible transitions, first from the cubic antifluorite (Fm3¯m) phase to an orthorhombic anticotunnite (Pnma) phase at about 13 GPa, followed by a transition to the hexagonal Ni2In-type (P63/mmc) structure above 30 GPa, as previously predicted by ab initio density functional theory calculations.

High-pressure synchrotron Mössbauer and X-ray diffraction studies: Exploring the structure-related valence fluctuation in EuNi2P2

The high-pressure effect on valence fluctuation of the ThCr2Si2-type intermetallic compound EuNi2P2 has been investigated using in situ synchrotron Mössbauer spectroscopy (SMS). The isomer shift of 151Eu in EuNi2P2 increases monotonically with increasing pressure up to 50GPa, suggesting a valence transition of the Eu from mixed toward trivalent. The synchrotron angle-dispersive X-ray diffraction (AD-XRD) experiment shows that EuNi2P2 remains in the tetragonal structure up to 32.5GPa at room temperature. We propose that the evolutions of bonding distance with pressure have an obvious effect on the valence fluctuation.

High-pressure X-ray diffraction, Raman, and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure.

Magnesium chloride (MgCl2) with the rhombohedral layered CdCl2-type structure (α-MgCl2) has been studied experimentally using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. The results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI2-type structure (β-MgCl2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. This observation is unusual, as it contradicts with the general structural behavior of highly compressed AB2 compounds.

High-Pressure-Induced Planarity of the Molecular Arrangement in Maleic Anhydride

Maleic anhydride, an industrially important chemical, was investigated by conducting in situ high-pressure Raman scattering and synchrotron angle-dispersive X-ray diffraction (ADXRD) experiments at a pressure of up to 1.0 GPa. Drastic discontinuities of Raman modes at 0.5 GPa indicated that a phase transition occurred when pressure was elevated. This transformation is further discussed by analysis of the ADXRD results. The Raman spectra and X-ray diffraction patterns of the recovered samples indicated that this pressure-induced transformation is reversible. The calculated results by the first-principle method indicated that the pressure-induced planarity of molecular arrangement is the mechanism of this transition. This study shows that the pressure-induced phase transition of maleic anhydride at 0.5 GPa is derived from supramolecular rearrangements.

Pressure-Induced Structural and Electronic Transition in Sr2ZnWO6 Double Perovskite.

High-pressure structural and electrical properties of Sr2ZnWO6 double perovskite were investigated using in situ angle-dispersive synchrotron X-ray diffraction (XRD), Raman, and alternating current (AC) impedance spectroscopy. A structural transition from monoclinic (P21/n) to triclinic (P1̅) phase around 9 GPa was observed due to the pressure-induced distortion of (W, Zn)O6 octahedron. In situ high-pressure Raman spectroscopy showed the increasing interaction among O-W-O in WO6 octahedron with pressure and a transition pressure consistent with the XRD results. From the AC impedance spectroscopy measurements, the resistivity increased steeply by ∼1 order of magnitude around 11 GPa, indicating an electronic transition accompanying the symmetry change. The increase in the interaction among O-W-O enhances the attraction of O(2-) electrons toward W(6+), thus increasing the covalence, which in turn lowers the charge transfer energy between O(2-) and W(6+) and induces the resistivity increase under high pressure.

Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure

Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr2S3) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr2S3 near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7–15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr2S3 based applications under extreme conditions.

Elastic, magnetic and electronic properties of iridium phosphide Ir2P.

Cubic (space group: Fmm) iridium phosphide, Ir2P, has been synthesized at high pressure and high temperature. Angle-dispersive synchrotron X-ray diffraction measurements on Ir2P powder using a diamond-anvil cell at room temperature and high pressures (up to 40.6 GPa) yielded a bulk modulus of B0 = 306(6) GPa and its pressure derivative B0′ = 6.4(5). Such a high bulk modulus attributed to the short and strongly covalent Ir-P bonds as revealed by first – principles calculations and three-dimensionally distributed [IrP4] tetrahedron network. Indentation testing on a well–sintered polycrystalline sample yielded the hardness of 11.8(4) GPa. Relatively low shear modulus of ~64 GPa from theoretical calculations suggests a complicated overall bonding in Ir2P with metallic, ionic, and covalent characteristics. In addition, a spin glass behavior is indicated by magnetic susceptibility measurements.

High-pressure structural study ofMnF2

Manganese fluoride $({\mathrm{MnF}}_{2})$ with the tetragonal rutile-type structure has been studied using a synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy in a diamond anvil cell up to 60 GPa at room temperature combined with first-principles density functional calculations. The experimental data reveal two pressure-induced structural phase transitions with the following sequence: rutile $\ensuremath{\rightarrow} {\mathrm{SrI}}_{2}$ type (3 GPa)$\ensuremath{\rightarrow} \ensuremath{\alpha}\ensuremath{-}{\mathrm{PbCl}}_{2}$ type (13 GPa). Complete structural information, including interatomic distances, has been determined in the case of ${\mathrm{MnF}}_{2}$ including the exact structure of the debated first high-pressure phase. First-principles density functional calculations confirm this phase transition sequence, and the two calculated transition pressures are in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phases. The results are discussed in line with the possible practical use of rutile-type fluorides in general and specifically ${\mathrm{MnF}}_{2}$ as a model compound to reveal the HP structural behavior of rutile-type ${\mathrm{SiO}}_{2}$ (Stishovite).

Phase Transition for Zinc Sulfide Nanosheets under High Pressure

This study describes the pressure-induced behavior of ZnS nanosheets by synchrotron angle-dispersive X-ray diffraction (ADXD) measurement up to 32.7 GPa. ZnS nanosheets transform from zinc blende structure to rock salt phase at 13.1 GPa and subsequently to a Cmcm structure at 20.3 GPa. The transition to the Cmcm structure is irreversible for ZnS nanomaterials at a much lower critical pressure than required for ZnS bulk materials. The special morphology of ZnS nanosheets plays a crucial role in the transition to Cmcm structures at comparatively low pressure. Continuous changes in lattice volume in the absence of volume collapse are observed after the transition from rock salt to the Cmcm structure occurs.

Structural and magnetic transition in stainless steel Fe-21Cr-6Ni-9Mn up to 250 GPa**Project supported by the National Natural Science Foundation of China (Grant Nos. U1230201, 11274281, and 11304294), the Industrial Technology Development Program, China (Grant No. 9045140509), and the Funds from the Chinese Academy of Sciences (Grant Nos. KJCX2-SW-N03 and KJCX2-SW-N20).

Stainless steel Fe-21Cr-6Ni-9Mn (SS 21-6-9), with ∼21% Cr, ∼6% Ni, and ∼9% Mn in weight percentage, has wide applications in extensive fields. In the present study, SS 21-6-9 is compressed up to 250 GPa, and its crystal structures and compressive behaviors are investigated simultaneously using the synchrotron angle-dispersive x-ray diffraction technique. The SS 21-6-9 undergoes a structural phase transition from fcc to hcp structure at ∼12.8 GPa with neglectable volume collapse within the determination error under the quasi-hydrostatic environment. The hcp structure remains stable up to the highest pressure of 250 GPa in the present experiments. The antiferromagnetic-to-nonmagnetic state transition of hcp SS 21-6-9 with the changes of inconspicuous density and structure, is discovered at ∼50 GPa, and revealed by the significant change in c/a ratio. The hcp SS-21-6-9 is compressive anisotropic: it is more compressive in the c-axis direction than in the a-axis direction. Both the equations of states (EOSs) of fcc and hcp SS 21-6-9, which are in accordance with those of fcc and hcp pure irons respectively, are also presented. Furthermore, the c/a ratio of hcp SS 21-6-9 at infinite compression, R∞, is consistent with the values of pure iron and Fe–10Ni alloy.

Compressibility and equation of state of beryl (Be3Al2Si6O18) by using a diamond anvil cell and in situ synchrotron X-ray diffraction

High-pressure single-crystal synchrotron X-ray diffraction was carried out on a single crystal of natural beryl compressed in a diamond anvil cell. The pressure-volume (P-V) data from room pressure to 9.51 GPa were fitted by a third-order Birch-Murnaghan equation of state (BM-EoS) and resulted in unit-cell volume V-0 = 675.5 +/- 0.1 angstrom(3), isothermal bulk modulus K-0 = 180 +/- 2 GPa, and its pressure derivative K-0' = 4.2 +/- 0.5. We also calculated V-0 = 675.5 +/- 0.1 angstrom(3) and K-0 = 181 +/- 1GPa with fixed K-0' at 4.0 and then obtained the axial moduli for a (K-a0)-axis and c (K-c0)-axis of 209 +/- 1 and 141 +/- 2 GPa by "linearized" BM-EoS approach. The axial compressibilities of a-axis and c-axis are beta(a) = 1.59 x 10(-3) GPa(-1) and beta(c) = 2.36 x 10(-3) GPa(-1) with an anisotropic ratio of beta(a):beta(c) = 0.67:1.00. On the other hand, the pressure-volume-temperature (P-V-T) EoS of the natural beryl has also been measured at temperatures up to 750 K and at pressures up to 16.81 GPa, using diamond anvil cell in conjunction with in situ synchrotron angle-dispersive powder X-ray diffraction. The P-V data at room temperature and at a pressure range of 0.0001-15.84 GPa were then analyzed by third-order BMEoS and yielded V-0 = 675.3 +/- 0.1 angstrom(3), K-0 = 180 +/- 2 GPa, K-0' = 4.2 +/- 0.3. With K-0' fixed to 4.0, we also obtained V-0 = 675.2 +/- 0.1 angstrom(3) and K-0 = 182 +/- 1 GPa. Consequently, we fitted the P-V-T data with high-temperature BM-EoS approach using the resultant K-0' (4.2) from room-temperature BM-EoS and then obtained the thermoelastic parameters of V-0 = 675.3 +/- 0.2 angstrom(3), K-0 = 180 +/- 1 GPa, temperature derivative of the bulk modulus (partial derivative K/partial derivative T)(P) = -0.01 7 +/- 0.004 GPa K-1, and thermal expansion coefficient at ambient conditions alpha(0) = (2.82 +/- 0.74) x 10(-6) K-1. Present results were also compared with previous studies for beryl. From the comparison of these fittings, we propose to constrain K-0 = 180 GPa and K-0' = 4.2 for beryl. And we also observed that beryl exhibits anisotropic thermal expansion at relatively low temperatures, which is very consistent with previous studies. Furthermore, no phase transition was observed in the entire pressure and temperature range (up to 16.84 GPa and 750 K) of this study for the natural beryl.

Structural and Vibrational Study of Pseudocubic CdIn2Se4 under Compression

We report a comprehensive experimental and theoretical study of the structural and vibrational properties of α-CdIn2Se4 under compression. Angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy evidence that this ordered-vacancy compound with pseudocubic structure undergoes a phase transition (7 GPa) toward a disordered rocksalt structure as observed in many other ordered-vacancy compounds. The equation of state and the pressure dependence of the Raman-active modes of this semiconductor have been determined and compared both to ab initio total energy and lattice dynamics calculations and to related compounds. Interestingly, on decreasing pressure, at ∼2 GPa, CdIn2Se4 transforms into a spinel structure which, according to calculations, is energetically competitive with the initial pseudocubic phase. The phase behavior of this compound under compression and the structural and compressibility trends in AB2Se4 selenides are discussed.

Deviatoric stress-induced phase transitions in diamantane.

The high-pressure behavior of diamantane was investigated using angle-dispersive synchrotron x-ray diffraction (XRD) and Raman spectroscopy in diamond anvil cells. Our experiments revealed that the structural transitions in diamantane were extremely sensitive to deviatoric stress. Under non-hydrostatic conditions, diamantane underwent a cubic (space group Pa3) to a monoclinic phase transition at below 0.15 GPa, the lowest pressure we were able to measure. Upon further compression to 3.5 GPa, this monoclinic phase transformed into another high-pressure monoclinic phase which persisted to 32 GPa, the highest pressure studied in our experiments. However, under more hydrostatic conditions using silicone oil as a pressure medium, the transition pressure to the first high-pressure monoclinic phase was elevated to 7-10 GPa, which coincided with the hydrostatic limit of silicone oil. In another experiment using helium as a pressure medium, no phase transitions were observed to the highest pressure we reached (13 GPa). In addition, large hysteresis and sluggish transition kinetics were observed upon decompression. Over the pressure range where phase transitions were confirmed by XRD, only continuous changes in the Raman spectra were observed. This suggests that these phase transitions are associated with unit cell distortions and modifications in molecular packing rather than the formation of new carbon-carbon bonds under pressure.

X-ray diffraction studies of Sr3Cr2O8 and Ba3Cr2O8 at high pressures

The chromates Sr3Cr2O8 and Ba3Cr2O8 have been investigated by in situ synchrotron angle-dispersive X-ray diffraction in diamond anvil cells at room temperature up to 27.6 and 26.0GPa, respectively. A phase transition of Sr3Cr2O8 was observed at 21.9GPa and room temperature, and no phase change occurred for Ba3Cr2O8 up to 26.0GPa in this study. The P–V data was fitted by the second-order Birch–Murnaghan equation of state, and the isothermal bulk modulus B0 was obtained as 97.0±1.3GPa and 89.7±2.7GPa for Sr3Cr2O8 and Ba3Cr2O8, respectively. The structural anisotropy increases with pressure increasing, and the a-axis is more compressible than the c-axis for both compounds.

Superior solid solubility of MnSiO3 in CaSiO3 perovskite

The silicate perovskite phase relation between CaSiO3 and MnSiO3 was investigated at 35–52 GPa and at 1,800 K using laser-heated diamond anvil cells combined with angle-dispersive synchrotron X-ray diffraction and energy-dispersive X-ray spectroscopic chemical analyses with scanning or transmission electron microscopy. We found that MnSiO3 can be incorporated into CaSiO3 perovskite up to 55, and 20 mol % of CaSiO3 is soluble in MnSiO3 perovskite. The range of 55–80 mol % of MnSiO3 in the CaSiO3–MnSiO3 perovskite system could be immiscible. We also observed that the two perovskite structured phases of the Mn-bearing CaSiO3 and the Ca-bearing MnSiO3 coexisted at these conditions. The Mn-bearing CaSiO3 perovskite has non-cubic symmetry and the Ca-bearing MnSiO3 perovskite has an orthorhombic structure with space group Pbnm. All the perovskite structured phases in the CaSiO3–MnSiO3 system convert to the amorphous phase during pressure release. MnSiO3 is the first chemical component confirmed to show such a superior solid solubility in CaSiO3 perovskite.

High-pressure structural transformations of PbCrO4 up to 51.2 GPa: An angle-dispersive synchrotron X-ray diffraction study

We report on high-pressure X-ray diffraction measurements up to 51.2GPa in PbCrO4 at room temperature. Three high-pressure phases with structures different than the ambient-pressure monazite-type (P21/n) are reported. One phase transition was found at 3.8GPa to an isomorphic structure to monazite. A second transition occurs at 11.1GPa. After this transition, the coexistence of tetragonal (I41/a) and monoclinic (P21) structures is detected up to 21.1GPa. Beyond this pressure and up to 51.2GPa, only the high-pressure monoclinic phase is observed. Upon decompression all structural changes are reversible. Finally, the axial compressibilities for the different phases have been determined as well as the equations of state.

P–V–T equation of state of molybdenite (MoS2) by a diamond anvil cell and in situ synchrotron angle-dispersive X-ray diffraction

The pressure–volume–temperature (P–V–T) equation of state (EoS) of a natural molybdenite (MoS2) has been measured at high temperature up to 700K and high pressures up to 18.26GPa, by using in situ angle-dispersive X-ray diffraction and diamond anvil cell. Analysis of room-temperature P–V data to a third-order Birch–Murnaghan EoS yields: V0=107.0±0.1Å3, K0=67±2GPa and K′0=5.0±0.3. With K′0 fixed to 4.0, we obtained: V0=106.7±0.1Å3 and K0=74.5±0.8GPa. Fitting of our P–V–T data by means of the high-temperature third order Birch–Murnaghan equations of state, gives the thermoelastic parameters: V0=107.0±0.1Å3, K0=69±2GPa, K′0=4.7±0.2, (∂K/∂T)P=−0.021±0.003GPaK−1, a=(2.2±0.7)×10−5K−1 and b=(2.9±0.8)×10−8K−2. The temperature derivative of the bulk modulus and thermal expansion coefficient of MoS2 are obtained for the first time. Present results are also compared with previously studies determined the elastic properties of MoS2 and WS2.

High-pressure and temperature investigations of energetic materials

Static high-pressure measurements are extremely useful for obtaining thermodynamic and phase stability information from a wide variety of materials. However, studying energetic materials can be challenging when extracting information from static high-pressure measurements. Energetic materials are traditionally C, H, N, O compounds with low crystalline symmetry, producing weak signal in commonly performed x-ray diffraction measurements. The small sample volume available in a static high-pressure cell exacerbates this issue. Additionally, typical hydrostatic compression media, such as methanol/ethanol, may react with many energetic materials. However, characterization of their thermodynamic parameters and phase stability is critical to understanding explosive performance and sensitivity. Crystalline properties, such as bulk modulus and thermal expansion, are necessary to accurately predict the behaviour of shocked solids using hydrodynamic codes. In order to obtain these values, equations of state of various energetic materials were investigated using synchrotron angle-dispersive x-ray diffraction experiments at static high-pressure and temperature. Intense synchrotron radiation overcomes the weak x-ray scattering of energetic materials in a pressure cell. The samples were hydrostatically compressed using a non-reactive hydrostatic medium and heated using a heated diamond anvil cell. Pressure - volume data for the materials were fit to the Birch-Murnaghan and Vinet formalisms to obtain bulk modulus and its first pressure derivative. Temperature - volume data at ambient pressure were fit to obtain the volume thermal expansion coefficient. Data from several energetic materials will be presented and compared.