Angle-dispersive X-ray Diffraction Data Research Articles

High‐pressure studies of Mn2(C2H6N6)4(NO3)4·2H2O by Raman scattering, infrared absorption, and synchrotron X‐ray diffraction

AbstractMn2(C2H6N6)4(NO3)4·2H2O (Mn) as one of the energetic coordination complexes was chosen for high‐pressure research. In this work, Mn was analyzed by in situ Raman scattering, infrared absorption, and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) technologies up to ~20 GPa at room temperature. The vibrational modes of Mn at ambient pressure were comprehensively resolved based on the experimental results. Detailed spectral analyses revealed that Mn underwent three pressure‐induced phase transitions at 0.5, 2.5, and 5.7 GPa, respectively. ADXRD experiments confirmed the existence of these three phase transitions in Raman and infrared spectra analyses. Based on the analysis of the vibrational spectra and the changes of lattice parameters under pressure, it can be considered that the deformation of the 3‐hydrazino‐4‐amino‐1, 2, 4‐triazole (HATr) ligand led to the first phase transition, and the distortion of the triazole ring induced the second phase transition, and the rearrangement of the hydrogen bonds resulted in the third phase transition. In addition, it can be inferred from Raman spectra and ADXRD data that Mn may have experienced the abnormal expansion during the first phase transition. This work may lay the foundation for further investigating the structure and properties of energetic coordination complexes under pressure.

Pressure-Induced Emission (PIE) and Phase Transition of a Two-dimensional Halide Double Perovskite (BA)4 AgBiBr8 (BA=CH3 (CH2 )3 NH3 + ).

Two-dimensional (2D) halide perovskites have attracted significant attention due to their compositional flexibility and electronic diversity. Understanding the structure-property relationships in 2D double perovskites is essential for their development for optoelectronic applications. In this work, we observed the emergence of pressure-induced emission (PIE) at 2.5 GPa with a broad emission band and large Stokes shift from initially nonfluorescent (BA)4 AgBiBr8 (BA=CH3 (CH2 )3 NH3 + ). The emission intensity increased significantly upon further compression up to 8.2 GPa. Moreover, the band gap narrowed from the starting 2.61 eV to 2.19 eV at 25.0 GPa accompanied by a color change from light yellow to dark yellow. Analysis of combined in situ high-pressure photoluminescence, absorption, and angle-dispersive X-ray diffraction data indicates that the observed PIE can be attributed to the emission from self-trapped excitons. This coincides with [AgBr6 ]5- and [BiBr6 ]3- inter-octahedral tilting which cause a structural phase transition. High-pressure study on (BA)4 AgBiBr8 sheds light on the relationship between the structure and optical properties that may improve the material's potential applications in the fields of pressure sensing, information storage and trademark security.

Exploring the compression behavior of HP-BiNbO4 under high pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 51472171 and 11427810) and the Chinese Academy of Sciences (Grant Nos. KJCX2-SW-NO3 and KJCX2-SW-N20).

In the present work, a third form, the so-called HP-BiNbO4 synthesized at high pressure and high temperature is investigated with the in-situ angle-dispersive x-ray diffraction (ADXRD) measurements under high pressure. We explore the compression behavior and phase stability of HP-BiNbO4. The structure of HP-BiNbO4 is first determined. The x-ray diffraction data reveal that the structure HP-BiNbO4 is stable under pressures up to 24.1 GPa. The ADXRD data yield a bulk modulus Ko = 185(7) GPa with a pressure derivative Ko′ = 2.9(0.8). Furthermore, the data are compared with those of other ABO4 compounds. The results show that the bulk modulus of HP-BiNbO4 (about 185 GPa) is slightly higher than that of tetragonal BiVO4 and significantly greater than those of the tungstates and molybdates.

Pressure-induced disordering and phase transformations in Eu2Zr2O7 pyrochlore

ABSTRACT The structural properties of pyrochlore Eu2Zr2O7 under high pressure have been studied by using Raman spectroscopy and in situ angle-dispersive X-ray diffraction (ADXRD). The results of Raman spectra indicate that Eu2Zr2O7 undergoes a reversible structural change around 21.2 GPa. The results of Rietveld refinements from in situ ADXRD data indicate that the ordered pyrochlore structure (Fd-3m) transforms to the defect-cotunnite structure (Pnma) at 26.5 GPa. The phase transition is irreversible and the transformation process is mainly induced by the accumulations of anti-site defects of the cation sublattice and Frenkel defects on the anion sublattice. Besides, the <Zr–O> bonds should play a more important role than the <Eu–O> bonds in the process of the phase transformation.

Thermal equation of state of natural tourmaline at high pressure and temperature

Synchrotron-based in situ angle-dispersive X-ray diffraction experiments were conducted on a natural uvite-dominated tourmaline sample by using an external-heating diamond anvil cell at simultaneously high pressures and temperatures up to 18 GPa and 723 K, respectively. The angle-dispersive X-ray diffraction data reveal no indication of a structural phase transition over the P–T range of the current experiment in this study. The pressure–volume–temperature data were fitted by the high-temperature Birch–Murnaghan equation of state. Isothermal bulk modulus of K 0 = 96.6 (9) GPa, pressure derivative of the bulk modulus of $$K_{0}^{\prime } = 12.5 \;(4)$$ , thermal expansion coefficient of α 0 = 4.39 (27) × 10−5 K−1 and temperature derivative of the bulk modulus (∂K/∂T) P = −0.009 (6) GPa K−1 were obtained. The axial thermoelastic properties were also obtained with K a0 = 139 (2) GPa, $$K_{a0}^{\prime }$$ = 11.5 (7) and α a0 = 1.00 (11) × 10−5 K−1 for the a-axis, and K c0 = 59 (1) GPa, $$K_{c0}^{\prime }$$ = 11.4 (5) and α c0 = 2.41 (24) × 10−5 K−1 for the c-axis. Both of axial compression and thermal expansion exhibit large anisotropic behavior. Thermoelastic parameters of tourmaline in this study were also compared with that of the other two ring silicates of beryl and cordierite.

Crystal behavior of potassium bromate under compression.

We report on high-pressure angle-dispersive X-ray diffraction data up to 15 GPa and ab initio total-energy calculations up to 242 GPa for KBrO3. No phase transition was found below 15 Pa in contrast to previously reported data. Its experimental bulk modulus in the quasi-hydrostatic regime is B0 = 18.8 (9) GPa with a bulk modulus pressure derivative B'0 = 8.2 (4). However, according to our ab initio calculations, KBrO3 significantly reduces its rhombohedral distortion via small cooperative movements of the atoms and the structure progressively approaches the cubic symmetry, where the KBr subarray would adopt a topology similar to that of the corresponding B2-type bromide. This rearrangement of atoms is directly related to the Buerger's mechanism of the B1-B2 phase transition for halides, confirming that cations (second neighbors) do not arrange in an arbitrary way. The O atoms forming the [BrO3] pyramidal units move smoothly with pressure to the center of the [K8] cube faces, where electron localization function calculations present their maxima in other B2-type compounds, eventually adopting the perovskite-type structure at P ≃ 152 GPa. Our data on KBrO3 has been compared with chemically substituted isostructural halates, providing new insights on the compressibility of this family of compounds.

Crystal Structure of Sinhalite MgAlBO4 under High Pressure

We report on high-pressure angle-dispersive X-ray diffraction data up to 27 GPa for natural MgAlBO4 sinhalite mineral and ab initio total energy calculations. The experimental bulk modulus of sinhalite is B0 = 171(3) GPa with a first-pressure derivative of B0′ = 4.2(3). A comparison with other olivine-type compounds shows that the value for B0 is 27% larger than that of Mg2SiO4 forsterite and 29% smaller than that of Al2BeO4 chrysoberyl. These differences are interpreted, on the basis of our ab initio calculations, in terms of the relative incompressibility of Al–O bonds in AlO6 octahedra (with a calculated bulk modulus of 250(1) GPa) as compared to Mg–O bonds in MgO6 octahedra (with a calculated bulk modulus of 130(1) GPa). The spatial cation distribution in the Pbnm orthorhombic unit cell and different polyhedral compressibilities entails a strong anisotropic compression comparable to that of forsterite. The axial compressibilities are 1.06(2) × 10–3, 2.17(2) × 10–3, and 1.30(3) × 10–3 GPa–1 for a, b, and c axes, respectively. The crystal chemistry of sinhalite under compression is compared to that of other olivine-like compounds. Compressibility trends and possible high-pressure phases are discussed.

Structural Studies on nanocrystalline ZnS and CdS

II-VI semiconductor nanocrystals have attracted much attention due to their size dependent properties ranging from electronic to biological regimes. Herein results of ZnS and CdS ADXRD (Angle dispersive X-ray diffraction) data, recorded in transmission mode, on BL-11 Beamline of INDUS Synchrotron are reported. Semiconductors obtained using wet chemical co-precipitation method, were kept for a few hours in the deep freezer. The wavelength of x-rays was 0.04666 nm (27 keV). A MAR 3450 image plate was used as detector. Sample to detector distance was 185.9178 mm. XRD data were extracted using fit2d. ADXRD pattern was recorded in transmission mode. The fityk program was used to fit pseudo Voigt A function to the ADXRD data to get the half width at half maximum (HWHM) of the peaks. These HWHMs values as well as the Scherrer formula yielded the particle sizes. The Neilson-Riley method was used to refine the lattice parameters. Results of the ADXRD data analyses for both ZnS and CdS are given below:The Particle size (nm), Bravais Lattice, Lattice parameter (nm) and Eg (eV) [UV abs spectra] for ZnS are 2.81, F¯43m, 0.5371 and 3.82 respectively while for CdS these values are 3.03, F¯43m, 0.580, 2.59 respectively. From these data the metal-S and Metal-Metal distances were calculated and were found out for ZnS to be 0.2326 nm and 0.3798 nm while for CdS these distances are 0.251 nm and 0.41 nm respectively. These data match well with the literature/1/. Particle sizes were in agreement with Brus's /2/ method. Acknowledgements: One of the authors (SDD) acknowledges the financial assistance from the University Grant Commission, New Delhi (F-37/147/2009(SR)). The authors are also grateful to Dr. S. K. Deb, Head, INDUS Synchrotron Users' Division, Raja Ramanna Center for Advanced Technology, Indore, (M.P.) India.

Reversible Structural Phase Transition in ZnV2O6 at High Pressures

The structural and electrical properties of ZnV2O6 under high pressure have been studied using Raman spectroscopy, in situ angle dispersive X-ray diffraction (ADXRD), and alternating current (AC) impedance spectroscopy. The results of Raman spectra indicate that ZnV2O6 undergoes a reversible structural change around 16.6 GPa, as evidenced by the appearance of new peaks. The results of Rietveld refinements from in situ ADXRD data indicate that the monoclinic symmetry (C2/m) is retained up to 16.0 GPa and the C2 phase comes to coexist between 16.0 and 16.9 GPa. Above 16.9 GPa, the high-pressure phase can be distinguished only as the C2 structure. The transformation process from the C2/m phase to the C2 phase is mainly caused by the more distorted ZnO6 octahedra and VO6 octahedra at higher pressures. The equal bond distances Zn–O2 and V–O3 in the C2/m phase become unequal in the C2 phase. Furthermore, the measurements of the AC impedance spectroscopy of ZnV2O6 reveal obvious changes in its electrical transpo...

High-pressure synthesis and in-situ high pressure x-ray diffraction study of cadmium tetraphosphide

Pure-phase polycrystalline cadmium tetraphosphide (CdP4) has been successfully synthesized under high pressures in a large volume cubic press, and the pressure–temperature (P-T) formation boundary of CdP4 from the Cd–P binary system has been determined. The equation of state of monoclinic CdP4 has also been evaluated by synchrotron-radiation angle-dispersive X-ray diffraction (ADXRD) under quasihydrostatic compression up to 26.4 GPa in a diamond-anvil cell. The ADXRD data yield a bulk modulus B0 = 94 ± 9 GPa with a pressure derivative B0′ = 8.0. The experimental data are discussed and compared to the results of first-principles calculations.

High-pressure study of the behavior of mineral barite by x-ray diffraction

In this paper, we report the angle-dispersive x-ray diffraction data of barite, BaSO${}_{4}$, measured in a diamond-anvil cell up to a pressure of 48 GPa, using three different fluid pressure-transmitting media (methanol-ethanol mixture, silicone oil, and He). Our results show that BaSO${}_{4}$ exhibits a phase transition at pressures that range from 15 to 27 GPa, depending on the pressure media used. This indicates that nonhydrostatic stresses have a crucial role in the high-pressure behavior of this compound. The new high-pressure (HP) phase has been solved and refined from powder data, having an orthorhombic $P$2${}_{1}$2${}_{1}$2${}_{1}$ structure. The pressure dependence of the structural parameters of both room- and HP phases of BaSO${}_{4}$ is also discussed in light of our theoretical first-principles total-energy calculations. Finally, a comparison between the different equations of state obtained in our experiments is reported.

X-ray diffraction measurements of Mo melting to 119 GPa and the high pressure phase diagram

In this paper, we report angle-dispersive X-ray diffraction data of molybdenum melting, measured in a double-sided laser-heated diamond-anvil cell up to a pressure of 119 GPa and temperatures up to 3400 K. The new melting temperatures are in excellent agreement with earlier measurements up to 90 GPa that relied on optical observations of melting and in strong contrast to most theoretical estimates. The X-ray measurements show that the solid melts from the bcc structure throughout the reported pressure range and provide no evidence for a high temperature transition from bcc to a close-packed structure, or to any other crystalline structure. This observation contradicts earlier interpretations of shock data arguing for such a transition. Instead, the values for the Poisson ratios of shock compressed Mo, obtained from the sound speed measurements, and the present X-ray evidence of loss of long-range order suggest that the 210 GPa (approximately 4100 K) transition in the shock experiment is from the bcc structure to a new, highly viscous, structured melt.

A scanning angle energy-dispersive X-ray diffraction technique for high-pressure structure studies in diamond anvil cells

A scanning angle diffraction technique with an energy-dispersive solid-state detector (SSD) and white synchrotron radiation has been developed for high-pressure structure studies in diamond anvil cells (DACs). This technique is similar to the CAESAR technique [Y. Wang, T. Uchida, R. Von Dreele, M.L. Rivers, N. Nishiyama, K. Funakoshi, A. Nozawa, and H. Kaneko, A new technique for angle-dispersive powder diffraction using an energy-dispersive setup and synchrotron radiation, J. Appl. Cryst. 37 (2004), p. 947] developed for large-volume presses, but extended to DAC applications with high spatial resolution. The main feature of the technique is the well-defined collimation in the beam path to the detector, which improves the signal-to-noise ratio significantly, compared to routine monochromatic angle-dispersive powder diffraction with area detectors. This is particularly useful and essential for low-scattering materials and for amorphous and liquid diffraction/scattering studies using DACs. Data collected from crystalline and amorphous samples in DACs show that a coarse 2θ scan (0.1–0.2° for crystals and 0.5° for amorphous structure) is sufficient to obtain reasonable diffraction resolution. The scanning angle energy-dispersive X-ray diffraction technique provides angle-dispersive X-ray diffraction (ADXD) data in multiple energies. Such multi-energy ADXD data carry much more information than regular single-energy ADXD, which could provide site-specific atomic structure information for full structure refinement.