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1.
Dr. Maxim Bykov Dr. Elena Bykova Dr. Michael Hanfland Dr. Hanns‐Peter Liermann Dr. Reinhard K. Kremer Prof. Dr. Robert Glaum Prof. Dr. Leonid Dubrovinsky Prof. dr. Sander van Smaalen 《Angewandte Chemie (International ed. in English)》2016,55(48):15053-15057
Titanium(III) phosphate, TiPO4 , is a typical example of an oxyphosphorus compound containing covalent P?O bonds. Single‐crystal X‐ray diffraction studies of TiPO4 reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high‐pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO4‐V is the first inorganic phosphorus‐containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO4‐V coexists with TiPO4‐IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO4‐II is found to be an incommensurately modulated phase whereas a lock‐in transition at about 7 GPa leads to TiPO4‐III with a fourfold superstructure compared to the structure of TiPO4‐I at ambient conditions. TiPO4‐II and TiPO4‐III are similar to the corresponding low‐temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin‐Peierls interactions. 相似文献
2.
Pressure‐Dependent Polymorphism and Band‐Gap Tuning of Methylammonium Lead Iodide Perovskite
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Shaojie Jiang Dr. Yanan Fang Dr. Ruipeng Li Dr. Hai Xiao Jason Crowley Dr. Chenyu Wang Prof. Timothy J. White Prof. William A. Goddard III Dr. Zhongwu Wang Dr. Tom Baikie Prof. Jiye Fang 《Angewandte Chemie (International ed. in English)》2016,55(22):6540-6544
We report the pressure‐induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) using in situ synchrotron X‐ray diffraction and laser‐excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin‐orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO3‐type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase‐mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction. 相似文献
3.
Zachary M. Geballe Hanyu Liu Ajay K. Mishra Muhtar Ahart Maddury Somayazulu Yue Meng Maria Baldini Russell J. Hemley 《Angewandte Chemie (International ed. in English)》2018,57(3):688-692
Recent theoretical calculations predict that megabar pressure stabilizes very hydrogen‐rich simple compounds having new clathrate‐like structures and remarkable electronic properties including room‐temperature superconductivity. X‐ray diffraction and optical studies demonstrate that superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. The results match the predicted cubic metallic phase of LaH10 having cages of thirty‐two hydrogen atoms surrounding each La atom. Upon decompression, the fcc‐based structure undergoes a rhombohedral distortion of the La sublattice. The superhydride phases consist of an atomic hydrogen sublattice with H?H distances of about 1.1 Å, which are close to predictions for solid atomic metallic hydrogen at these pressures. With stability below 200 GPa, the superhydride is thus the closest analogue to solid atomic metallic hydrogen yet to be synthesized and characterized. 相似文献
4.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(34):10326-10329
At 80 GPa, phases with the PH2 stoichiometry, which are composed of simple cubic like phosphorus layers capped with hydrogen atoms and layers of H2 molecules, are predicted to be important species contributing to the recently observed superconductivity in compressed phosphine. The electron–phonon coupling in these phases results from the motions of the phosphorus atoms and the hydrogen atoms bound to them. The role of the mobile H2 layers is to decrease the Coulomb repulsion between the negatively charged hydrogen atoms capping the phosphorus layers. An insulating PH5 phase, the structure and bonding of which is reminiscent of diborane, is also predicted to be metastable at this pressure. 相似文献
5.
Dominik Baumann Robin Niklaus Prof. Dr. Wolfgang Schnick 《Angewandte Chemie (International ed. in English)》2015,54(14):4388-4391
The chemical and physical properties of phosphorus oxonitride (PON) closely resemble those of silica, to which it is isosteric. A new high‐pressure phase of PON is reported herein. This polymorph, synthesized by using the multianvil technique, crystallizes in the coesite structure. This represents the first occurrence of this very dense network structure outside of SiO2. Phase‐pure coesite PON (coe‐PON) can be synthesized in bulk at pressures above 15 GPa. This compound was thoroughly characterized by means of powder X‐ray diffraction, DFT calculations, and FTIR and MAS NMR spectroscopy, as well as temperature‐dependent diffraction. These results represent a major step towards the exploration of the phase diagram of PON at very high pressures and the possibly synthesis of a stishovite‐type PON containing hexacoordinate phosphorus. 相似文献
6.
The present paper reports the phase progression in nano-crystalline oxides PrO2 and CeO2 up to pressures of 49 GPa and 35 GPa, respectively, investigated via in situ Raman spectroscopy at room temperature. The samples were characterized at ambient conditions using X-ray diffraction (XRD), AFM, and Raman spectroscopy and were found to be cubic with fluorite structure. With an increase in applied pressure the cubic bands were seen to steadily shift to higher wavenumbers for both the samples. However, we observed the appearance of a number of new peaks around a pressure of about 34.7 GPa in CeO2 and 33 GPa in PrO2 which were characteristic of an orthorhombic α-PbCl2 type structure. The mode Gruneisen parameters for both the phases were obtained from the pressure dependence of frequency shifts. On decompression, the high pressure phase existed down to a total release of pressure. 相似文献
7.
Songhao Guo Yongsheng Zhao Kejun Bu Yongping Fu Hui Luo Mengting Chen Matthew P. Hautzinger Yingqi Wang Song Jin Wenge Yang Xujie Lü 《Angewandte Chemie (International ed. in English)》2020,59(40):17533-17539
A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)2(GA)Pb2I7 (HA=n‐hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non‐luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above‐band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two‐fold higher PL emission compared with the pristine (HA)2(GA)Pb2I7. 相似文献
8.
X‐Ray Diffraction and Mössbauer Spectroscopy Studies of Pressure‐Induced Phase Transitions in a Mixed‐Valence Trinuclear Iron Complex
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Dr. Solveig R. Madsen Dr. Haraldur P. Gunnlaugsson Dr. Stephen A. Moggach Espen Eikeland Dr. Lai‐Chin Wu Dr. Olaf Leupold Dr. Jacob Overgaard Prof. Bo B. Iversen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9616-9623
The mixed‐valence complex Fe3O(cyanoacetate)6(H2O)3 ( 1 ) has been studied by single‐crystal X‐ray diffraction analysis at pressures up to 5.3(1) GPa and by (synchrotron) Mössbauer spectroscopy at pressures up to 8(1) GPa. Crystal structure refinements were possible up to 4.0(1) GPa. In this pressure range, 1 undergoes two pressure‐induced phase transitions. The first phase transition at around 3 GPa is isosymmetric and involves a 60° rotation of 50 % of the cyanoacetate ligands. The second phase transition at around 4 GPa reduces the symmetry from rhombohedral to triclinic. Mössbauer spectra show that the complex becomes partially valence‐trapped after the second phase transition. This sluggish pressure‐induced valence‐trapping is in contrast to the very abrupt valence‐trapping observed when compound 1 is cooled from 130 to 120 K at ambient pressure. 相似文献
9.
About Cesium Trichloromercurate(II) CsHgCl3: Solution of a Complex Superstructure and Behaviour under High Pressure By solving the crystal structure of CsHgCl3 a new uncommon distortion variant of the cubic perovskite type with extremely (2 + 2 + 2)‐distorted HgCl6 octahedra has been found. The trigonal superstructure with space group P32 and ninefold cell contents differs from the aristotype only so far, as 2/3 of the Cl‐atoms are moved away from their ideal positions leading to 3 pairs of different Hg–Cl distances with about 2.35 Å, 2.71 Å and 3.15 Å. The cations Cs+ and Hg2+ and the chloride ions with medium Hg–Cl distance keep the ideal positions of a cubic perovskite lattice. Due to the evenly distribution of the three different bonds in the three directions of cubic space the cell shows an almost perfect cubic metric. Raman spectra and powder diffraction experiments up to pressures of 5 GPa demonstrated that the ideal perovskite arrangement is stabilized with increasing pressure. The shift of the FT‐Raman bands show in agreement with spectra simulations that the Hg–Cl bonds are equalized, leading to a regular octahedral co‐ordination of the Hg atoms. The disappearance of the Raman spectrum at P > 3.4 GPa indicates that the high pressure phase forms an ideal cubic perovskite (a = 5.204(1) Å, Hg–Cl = 2.60 Å). 相似文献
10.
High pressure Raman spectroscopic measurements on nearly zero thermal expansion material TaO2F are carried out up to 19 GPa. Earlier report of high pressure X-ray diffraction studies shows two phase transitions, one at 0.7 and the other at 4 GPa with rhombohedral (R-3c) structure above 4 GPa, but the structure between 0.7 GPa and 4 GPa remained unclear. In high pressure Raman measurements, a reversible, cubic to rhombohedral phase transformation onsets around 0.8 GPa and gets completed at 4.4 GPa with all four predicted normal modes corresponding to R-3c phase and retaining the structure up to 19 GPa. A mixture of cubic and rhombohedral phases is observed between 0.8 and 4.4 GPa. Optically silent modes in the ambient cubic structure exhibit strong, broad Raman bands due to anionic (O/F) disorder in TaO2F altering the local symmetry and allowing for first order Raman scattering. On compression, these disorder induced first order Raman bands gradually decrease in intensity and disappear around 4.4 GPa due to inhibition of local distortion caused by anions, and the modes corresponding to the rhombohedral phase appear. This is a clear evidence of disorder-free rhombohedral single phase exists above 4.4 GPa in agreement with the reported HPXRD results. Temperature dependent Raman measurements reveal that the intensities of Raman bands remain almost unchanged with rise in temperature indicating static disorder in TaO2F. Disorder-induced first order Raman modes at 176, 212, 381 and 485 cm−1 soften with increase in pressure whereas the other modes show low positive Gruneisen parameter. The thermal expansion coefficient calculated using these Gruneisen parameters (−2.91 ppm K−1) is in fair agreement with the reported values (−1 to +1 ppm K−1). On the other hand, all four modes of disorder-free rhombohedral phase show the usual hardening behavior with increase in pressure contributing to positive thermal expansion. 相似文献
11.
Dr. Andrey Yu. Manakov Dr. Anna Yu. Likhacheva Dr. Vladimir A. Potemkin Dr. Andrey G. Ogienko Dr. Alexander V. Kurnosov Dr. Aleksei I. Ancharov 《Chemphyschem》2011,12(13):2476-2484
Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0–2 GPa), xenon (cubic structure I, pressure range 0–1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0–3 GPa) are presented. Approximation of the data using the cubic Birch–Murnaghan equation, P=1.5B0[(V0/V)7/3?(V0/V)5/3], gave the following results: for ethane hydrate V0=1781 Å3, B0=11.2 GPa; for xenon hydrate V0=1726 Å3, B0=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V0=5323 Å3, B0=8.8 GPa. In the last case, the approximation was performed within the pressure range 0–1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch–Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86 % of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen‐bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones. 相似文献
12.
The high‐pressure behavior of Si2N2O is studied for pressures up to 100 GPa using density functional theory calculations. The investigation of a manifold of hypothetical polymorphs leads us to propose two dense phases of Si2N2O, succeeding the orthorhombic ambient‐pressure polymorph at higher pressures:a defect spinel structure at moderate pressures and a corundum‐type structure at very high pressures. Taking into account the formation of silicon oxynitride from silicon dioxide and silicon nitride and its pressure dependence, we propose five pressure regions of interest for Si2N2O within the pseudo‐binary phase diagram SiO2‐Si3N4: (i) stability of the orthorhombic ternary phase of Si2N2O up to 6 GPa, (ii) a phase assemblage of coesite, stishovite, and β‐Si3N4 between 6 and 11 GPa, (iii) a possible defect spinel modification of Si2N2O between 11 and 16 GPa, (iv) a phase assemblage of stishovite and γ‐Si3N4 above 40 GPa, and (v) a possible ternary Si2N2O phase with corundum‐type structure beyond 80 GPa. The existence of both ternary high‐pressure phases of Si2N2O, however, depends on the delicate influence of configurational entropy to the free energy of the solid state reaction. 相似文献
13.
Akira Yoshiasa Genta Yagyu Tomokazu Ito Takamitu Yamanaka Takaya Nagai 《无机化学与普通化学杂志》2000,626(1):36-41
Crystal structures of the ambient pressure and temperature phase (phase I) and high pressure phase (phase II) in CuGeO3 were studied by means of the high pressure single‐crystal X‐ray diffraction method in a diamond anvil cell using high power X‐ray generator and imaging plate detector. The pressure dependence of the atomic displacements in the phase I was investigated under the hydrostatic pressure of 0.1 MPa and 2.9 and 3.9 GPa. The lattice is particularly compressive in the b direction. In phase I the rippled layers are formed by the corner‐shared chains of GeO4 tetrahedra and edge‐linked planar CuO4. Major effects of pressure, directly related to the shortening of the b‐axis, consist of an enhanced folding of the rippled layers towards the b‐direction and of a shortening of the weak Cu–O bond. The crystal structure of phase II is monoclinic, a = 4.935(57), b = 6.754(14), c = 6.208(11) Å, β = 92.67(3)°, space group; P21/c. The transition from phase I to II involves a corrugated arrangement of the both cation with some oxygens around the c‐axis. Ge ion at the transition point of 6.4 GPa changes its coordination number from four‐fold to five‐fold, and Cu ion occupies a position of seven‐fold site. The structure of phase II is explained as a slab structure having unique edge‐ and corner‐sharing arrangements of GeO5 and CuO7 polyhedra. The average Ge–O and Cu–O distances in phase II is 1.92 and 2.17 Å, respectively, at 6.5 GPa. 相似文献
14.
The Local Atomic Structures of Liquid CO at 3.6 GPa and Polymerized CO at 0 to 30 GPa from High‐Pressure Pair Distribution Function Analysis
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Dr. Nadine Rademacher Dr. Lkhamsuren Bayarjargal Dr. Wolfgang Morgenroth Prof. Dr. Björn Winkler Dr. Jennifer Ciezak‐Jenkins Dr. Iskander G. Batyrev Dr. Victor Milman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(36):11531-11539
The local atomic structures of liquid and polymerized CO and its decomposition products were analyzed at pressures up to 30 GPa in diamond anvil cells by X‐ray diffraction, pair distribution function (PDF) analysis, single‐crystal diffraction, and Raman spectroscopy. The structural models were obtained by density functional calculations. Analysis of the PDF of a liquid CO‐rich phase revealed that the local structure has a pronounced short‐range order. The PDFs of polymerized amorphous CO at several pressures revealed the compression of the molecular structure; covalent bond lengths did not change significantly with pressure. Experimental PDFs could be reproduced with simulations from DFT‐optimized structural models. Likely structural features of polymerized CO are thus 4‐ to 6‐membered rings (lactones, cyclic ethers, and rings decorated with carbonyl groups) and long bent chains with carbonyl groups and bridging atoms. Laser heating polymerized CO at pressures of 7 to 9 GPa and 20 GPa resulted in the formation of CO2. 相似文献
15.
The perovskite-related layered structure of La2Ti2O7 has been studied at pressures up to 30 GPa using synchrotron radiation powder X-ray diffraction (XRD) and Raman scattering. The XRD results indicate a pronounced anisotropy for the compressibility of the monoclinic unit cell. The ratio of the relative compressibilities along the [100], [010] and [001] directions is ∼1:3:5. The greatest compressibility is along the [001] direction, perpendicular to the interlayer. A pressure-induced phase transition occurs at 16.7 GPa. Both Raman and XRD measurements reveal that the pressure-induced phase transition is reversible. The high-pressure phase has a close structural relation to the low-pressure monoclinic phase and the phase transition may be due to the tilting of TiO6 octahedra at high pressures. 相似文献
16.
The binary alloy phase ϵ‐Ag7+xMg26–x with x ≈ 1 and small amounts of the β′‐AgMg phase crystallize by annealing of Ag–Mg alloys with starting compositions between 24–28 At‐% Ag at 390 to 420 °C. A model structure for the ϵ‐phase consisting of a fcc packing of Mackay clusters was derived from the known structure of the ϵ′‐Ag17Mg54 phase. Crystals of the ϵ‐phase were obtained by direct melting of the elements and annealing. The examination of a single crystal yielded a face‐centered cubic unit cell, space group Fm3 with a = 1761.2(5) pm. The refinement was started with the parameters of the model: wR2(all) = 0.0925 for 1093 symmetrically independent reflections. A refinement of the occupancy parameters indicated a partial replacement of silver for magnesium at two metal atom sites, resulting in the final composition ϵ‐Ag7+xMg26–x with x = 0.96(2). There are 264 atoms in the unit cell and the calculated density is 3.568 gcm–3. The topology of the model was confirmed. Mackay icosahedra are located at the lattice points of a face‐centered cubic lattice. Differences between model and refined structure and their effects on the powder patterns are discussed. The new binary structure type of ϵ‐Ag7+xMg26–x can be described in terms of the I3‐cluster concept. 相似文献
17.
《Journal of the Less Common Metals》1989,146(1-2):137-143
The variations in the volumes of CeSe and CeBe13 have been determined by powder X-ray diffraction in a diamond anvil cell up to 25 GPa at room temperature. In each case, the bulk modulus and its first pressure derivative have been determined. They do not indicate the presence of any negative contribution due to a Kondo volume-dependent interaction or a pressureinduced valence change. A crystallographic phase transformation to a cubic CsCl-type structure has been evidenced for CeSe above 18 GPa. 相似文献
18.
Jianyan Lin Xin Du Martin Rahm Hong Yu Haiyang Xu Guochun Yang 《Angewandte Chemie (International ed. in English)》2020,59(23):9155-9162
Fluorination is a proven method for challenging the limits of chemistry, both structurally and electronically. Here we explore computationally how pressures below 300 GPa affect the fluorination of several transition metals. A plethora of new structural phases are predicted along with the possibility for synthesizing four unobserved compounds: TcF7, CdF3, OsF8, and IrF8. The Ir and Os octaflourides are both predicted to be stable as quasi‐molecular phases with an unusual cubic ligand coordination, and both compounds formally correspond to a high oxidation state of +8. Electronic‐structure analysis reveals that otherwise unoccupied 6p levels are brought down in energy by the combined effects of pressure and a strong ligand field. The valence expansion of Os and Ir enables ligand‐to‐metal F 2p→M 6p charge transfer that strengthens M?F bonds and decreases the overall bond polarity. The lower stability of IrF8, and the instability of PtF8 and several other compounds below 300 GPa, is explained by the occupation of M?F antibonding orbitals in octafluorides with a metal‐valence‐electron count exceeding 8. 相似文献
19.
Sebastian Vogel Maxim Bykov Elena Bykova Sebastian Wendl Simon D. Kloß Anna Pakhomova Natalia Dubrovinskaia Leonid Dubrovinsky Wolfgang Schnick 《Angewandte Chemie (International ed. in English)》2020,59(7):2730-2734
Owing to its outstanding elastic properties, the nitride spinel γ‐Si3N4 is of considered interest for materials scientists and chemists. DFT calculations suggest that Si3N4‐analog beryllium phosphorus nitride BeP2N4 adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite‐type BeP2N4 by single‐crystal synchrotron X‐ray diffraction and report the phase transition into the spinel‐type phase at 47 GPa and 1800 K in a laser‐heated diamond anvil cell. The structure of spinel‐type BeP2N4 was refined from pressure‐dependent in situ synchrotron powder X‐ray diffraction measurements down to ambient pressure, which proves spinel‐type BeP2N4 a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel‐type BeP2N4 is an ultraincompressible material. 相似文献
20.
We have performed high-pressure synchrotron X-ray diffraction experiments on nanoparticles of pure tin dioxide (particle size ∼30 nm) and 10 mol % Fe-doped tin dioxide (particle size ∼18 nm). The structural behavior of undoped tin dioxide nanoparticles has been studied up to 32 GPa, while the Fe-doped tin dioxide nanoparticles have been studied only up to 19 GPa. We have found that both samples present at ∼13 GPa a second-order structural phase transition from the ambient pressure tetragonal rutile-type structure (P42/mnm) to an orthorhombic CaCl2-type structure (space group Pnnm). No phase coexistence was observed for this transition. Additionally, pure SnO2 presents a phase transition to a cubic structure at ∼24 GPa. The evolution of the lattice parameters with pressure and the room-temperature equations of state are reported for the different phases. The reported results suggest that the partial substitution of Sn by Fe induces an enhancement of the bulk modulus of SnO2. Results are compared with previous studies on bulk and nanocrystalline SnO2. The effects of pressure on Sn-O bonds are also analyzed. 相似文献