High Pressure Structural Stability Research Articles

Thermal equation of state of rhodium characterized by XRD in a resistively heated diamond anvil cell

The high-pressure and high-temperature structural, mechanical, and dinamical stability of rhodium has been investigated via synchrotron X-ray diffraction using a resistively heated diamond anvil cell and density functional theory. The isothermal compression data have been fitted with a Rydberg-Vinet equation of state (EoS) with best-fitting parameters V0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_0$$\\end{document} =55.046(16) Å3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}, K0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_0$$\\end{document} = 251(3) GPa, and K0′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K'_0$$\\end{document} = 5.7(2). The thermal equation of state has been determined based upon the data collected following four different isotherms and has been fitted to a Holland and Powell thermal equation-of-state model with α0=\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha _0=$$\\end{document}3.36(7)x10-5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-5}$$\\end{document}K-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}. The measured equation of state and structural parameters have been compared to the results of ab initio simulations. The agreement between theory and experiments is generally quite good. The present results solve controversies between previous studies which reported values of the bulk modulus from 240 to 300 GPa.

Dual Function of Hydrogen Bond and CEI to Enhanced Lithium-Ion Battery Performance.

The stability of the commercial electrolyte is linked to the internal solvent molecule, particularly in enhancing the stability of these molecules. Hereby, we introduce a dual function strategy involving hydrogen bond induced solvent molecules and the in situ fabrication cathode-electrolyte interphase (CEI) to address this issue. The additive N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide (DOTFA), with its oxazolidinyl and trifluoroacetamide functional units, establishes hydrogen bonds with the solvent, forming CEI films on the cathode surface that enhance the antioxidation ability of the electrolyte. These hydrogen bonds contribute to enhancing the high-pressure structural stability of the solvent molecule. Additionally, the uniform and robust in situ constructed CEI films act as a shield, protecting the cathode from various side reactions and enhancing interface compatibility. By incorporation of the DOTFA additive in the electrolyte, lithium-ion batteries with NCM811 cathodes exhibit excellent cycling performance. The work highlights the significance of dual function in solvent molecules and provides an effective method for enhancing the antioxidation ability of the electrolyte.

A comparative study of the high-pressure structural stability of zirconolite materials for nuclear waste immobilisation

We present a comparative study of the high-pressure behaviours of the nuclear waste immobilisation materials zirconolite-2M, −4M, –3O, and −3T. The materials are studied under high-pressure conditions using synchrotron powder X-ray diffraction. For zirconolite-2M we also performed density-functional theory calculations. A new triclinic crystal structure (space group P1¯), instead of the previously assigned monoclinic structure (space group C2/c) is proposed for zirconolite-2M. We named the triclinic structure as zirconolite-2TR. We also found that zirconolite-2TR undergoes a phase transition at 14.7 GPa to a monoclinic structure described by space group C2/c, which is different than the high-pressure structure previously proposed in the literature. These results are discussed in comparison with previous studies on zirconolite-2M and the related compound calzirtite. For the other three zirconolite structures (4M, 3O, and 3T) this is the first high-pressure study, and we find no evidence for pressure induced phase transitions in any of them. The linear compressibility of the studied compounds, as well as a room-temperature pressure–volume equation of state, are also presented and discussed.

Pressure-Driven Structural and Electronic Transitions in a Two-Dimensional Janus WSSe Crystal.

In this work, we presented the first report on the high-pressure structural stability and electrical transport characteristics in WSSe under different hydrostatic environments through Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy (HRTEM) coupled with first-principles theoretical calculations. For nonhydrostatic conditions, WSSe endured a phase transition at 15.2 GPa, followed by a semiconductor-to-metal crossover at 25.3 GPa. Furthermore, the bandgap closure was accounted for the metallization of WSSe as derived from theoretical calculations. Under hydrostatic conditions, ∼ 2.0 GPa pressure hysteresis was detected for the emergence of phase transition and metallization in WSSe because of the feeble deviatoric stress. Upon depressurization, the reversibility of the phase transition was substantiated by those of microscopic HRTEM observations under different hydrostatic environments. Our high-pressure investigation on WSSe advances the insightful understanding of the crystalline structure and electronic properties for the Janus transition-metal dichalcogenide (TMD) family and boosts prospective developments in functional devices.

Pressure-Induced Reverse Structural Transition of Calcite at Temperatures up to 873 K and Pressures up to 19.7 GPa

In situ Raman scattering and electrical conductivity experiments have been performed to investigate the structural phase transitions of calcite during the compressed and decompressed processes in a diamond anvil cell at temperatures of 298–873 K and pressures up to 19.7 GPa. Upon compression, calcite (CaCO3-I phase) underwent three structural phase transitions from CaCO3-I to CaCO3-II phases at 1.6 GPa, from CaCO3-II to CaCO3-III phases at 2.2 GPa, and from CaCO3-III to CaCO3-VI phases at 16.8 GPa under room temperature conditions, which were evidenced by the evolution of Raman peaks, as well as the discontinuities in the pressure-dependent Raman shifts and electrical conductivity. Upon decompression, the structural phase transitions from CaCO3-VI to CaCO3-III to CaCO3-II to CaCO3-I phases took place at the respective pressures of 5.4, 1.5, and 0.4 GPa, indicating the reversibility of calcite. Furthermore, an obvious ~11 GPa of pressure hysteresis was detected in the CaCO3-VI to CaCO3-III phase transition, whereas other reverse phase transition pressures were very close to those of compressed results. At three given representative pressure conditions (i.e., 10.5, 12.5, and 13.8 GPa), a series of electrical conductivity experiments were performed at temperature ranges of 323–873 K to explore the temperature-dependent relation of CaCO3-III to CaCO3-VI structural phase transition. With increasing pressure, the transition temperature between CaCO3-III and CaCO3-VI phases gradually decreases, which reveals an obviously negative temperature-pressure relation, i.e., P (GPa) = 19.219 (±1.105) − 0.011 (±0.002) T (K). Our acquired phase diagram of calcite can be employed to understand the high-pressure structural transitions and phase stability for carbonate minerals along various subducting slabs in the deep Earth’s interior.

High pressure structural stability of UO2 by evolutionary algorithm

High pressure structural stability of UO2 by evolutionary algorithm

High-pressure structural stability and bandgap engineering of layered tin disulfide

Two-dimensional layered metal dichalcogenides have attracted extensive attention because of their diverse physical properties and potential applications in electronics and optoelectronics. As an eco-friendly and earth abundant semiconductor, SnS2 displays limited optoelectronic applications due to its large and indirect bandgap. Pressure is a powerful tool to tune crystal structures and physical properties of materials. Here, we systematically investigate the structural stability and optical properties of 4H-SnS2 under high pressure. The crystal structure of 4H-SnS2 is stable up to 56 GPa without structural transition and layer sliding. Continuous lattice contraction is accompanied by gradual bandgap narrowing, which is reversible after releasing pressure. The continuous and reversible modulation of the crystal structure and bandgap on 4H-SnS2 suggest promising optoelectronic applications in the range of visible light based on two-dimensional layered metal dichalcogenides.

Structure–compressibility correlation among MoBx

Molybdenum forms a large number of borides with various stoichiometries. In this paper the trends in the compressibility behaviour among MoBx (x: 0.5, 1, 2 and 3) were investigated. High-pressure structural stability studies on MoB3 were carried out up to a pressure of 40 GPa using a Mao–Bell-type diamond anvil cell. The hexagonal structure remained stable up to 40 GPa. High-pressure X-ray diffraction data yielded a bulk modulus of 254 GPa and were in good agreement with computed bulk moduli of 258–295 GPa with various potentials. First-principles calculations were carried out to investigate the structural, elastic and mechanical properties of molybdenum borides based on generalized gradient approximation proposed by Perdew–Burke–Ernzerhof. The compressibility behaviour of MoBx (x = 0.5, 1, 2 and 3) showed parabolic trend and was explained in terms of electronic structure and mainly arose due to the partial charge density of boron.

High-pressure structural stability and melting performance of α-2,4-dinitroanisole

Energetic materials have to face variable environments throughout their life cycle. Therefore, revealing the evolvement of energetic materials under complex conditions is of great importance for their applications. As an energetic material, α-2,4-Dinitroanisole (α-DNAN) exhibits low sensitivity and can be used in the formulation of melt-cast insensitive munitions as a replacement for TNT. Despite numerous studies focusing on DNAN, the high-pressure investigation of DNAN is still limited. Using diamond anvil cell and resistance heating techniques, this study investigates the structural variation and melting performance of α-DNAN at high pressures. The results are as follows. A phase transition occurred at 1.5 ​GPa. The high-pressure phase kept stable and had the tendency to be amorphous at high pressures. The high-temperature and high-pressure Raman measurement and optical photographing illustrated that pressure significantly influenced the melting temperature of α-DNAN. From 0.6 to 1.2 and then to 1.9 ​GPa, the melting point increased from 130 ​°C to 182 ​°C and finally to 285 ​°C. When the pressure reached 1.9 ​GPa, decomposition occurred and was accompanied by a melting process. This high-pressure and high-temperature study of DNAN contributes to deeply understanding the structural stability of DNAN and provides important data for the manufacture and storage of DNAN.

First-principles study of high-pressure structural stability and mechanical properties of Ni2B

The structural stability and mechanical properties of Ni2B with I4/mcm space group under various external pressure are indagated utilizing the first-principle calculations. The calculated phonon dispersion curves, formation enthalpy and elastic constants clarify that I4/mcm phase has dynamical, thermodynamic and elastic stability. The theoretical elastic modulus by stress–strain method shows that the I4/mcm structure has a small anisotropy. The intrinsic mechanism affecting the mechanical properties of Ni2B structure is confirmed according to the calculated the ideal strength values under a series of strains and the two-dimensional electron localization function plots corresponding to the key several structural models. The comprehensive results manifest that the structural failure of Ni2B with I4/mcm symmetry mainly stems from the break of Ni-B covalent bond along the specific shear strain direction.

High pressure photoluminescence properties and structural stability of Eu doped AlN nanowires synthesized via a direct nitridation strategy

High-aspect-ratio Eu doped AlN (AlN:Eu) nanowires (NWs) were synthesized via direct nitridation strategy. The NWs exhibits a strong green emission of the 5d-4f transition under ultraviolet light excitation. Photoluminescence (PL) spectra and synchrotron angle-dispersive X-ray diffraction (ADXRD) for AlN:Eu NWs were performed under hydrostatic pressures up to above 30 GPa. The pressure-induced monotonic red-shift of emission band (dλ/dP ≈ 5.9 nm GPa−1), as well as changes in the emission band widths, have been correlated with pressure for visible-light optical pressure sensors. As the pressure reaches around 20 GPa, the phase transition of AlN:Eu NWs from the wurtzite to rocksalt was found by the appearance of a PL band and ADXRD peak. The enhancement of transition pressure and bulk modulus in AlN:Eu NWs as compared with other ions doped AlN is considered to be caused by co-dopants of Eu2+ and Eu3+ ions. This work provides an effective strategy for doping large-size rare-earth ions into wide band-gap nitride semiconductor, and demonstrates a straightforward pathway for tuning optical properties through pressure without modifying composition.

Exploration of pressure induced phase transitions and thermo-mechanical properties in LuX (X=As, Sb, Bi)

This paper reports the detailed first-principle calculations carried out to investigate the high pressure structural phase stability of lutetium pnictides (LuX, where X = As, Sb and Bi) up to 200 GPa. All of these compounds crystallize in the rocksalt type structure (B1 phase) at ambient condition. In LuAs our calculations suggest the occurrence of orthorhombic structure (Cmcm space group) at ∼ 53 GPa, which is close to the experimentally reported transition pressure of ∼57 GPa to an unresolved structure. This orthorhombic phase further transforms to a tetragonal structure (space group I4/amd) at ∼ 67 GPa. In LuSb and LuBi, B1 phase directly transforms to I4/amd structure at ∼20 GPa and ∼17 GPa, respectively. Upon further compression, in case of LuAs and LuSb, the I4/amd phase remains stable up to 200 GPa, however, in LuBi this tetragonal phase transforms to another tetragonal structure (space group P4/mmm). Also, using quasi-harmonic approximation, the temperature variation of various thermo-physical quantities, namely, bulk modulus, volume, volume thermal expansion coefficient, heat capacity, and Gruneisen parameter of these compounds for the ambient B1 phase have been determined in the present study.

Thermal equation of state of ruthenium characterized by resistively heated diamond anvil cell

The high-pressure and high-temperature structural and chemical stability of ruthenium has been investigated via synchrotron X-ray diffraction using a resistively heated diamond anvil cell. In the present experiment, ruthenium remains stable in the hcp phase up to 150 GPa and 960 K. The thermal equation of state has been determined based upon the data collected following four different isotherms. A quasi-hydrostatic equation of state at ambient temperature has also been characterized up to 150 GPa. The measured equation of state and structural parameters have been compared to the results of ab initio simulations performed with several exchange-correlation functionals. The agreement between theory and experiments is generally quite good. Phonon calculations were also carried out to show that hcp ruthenium is not only structurally but also dynamically stable up to extreme pressures. These calculations also allow the pressure dependence of the Raman-active E2g mode and the silent B1g mode of Ru to be determined.

High pressure structural stability of ThN: ab-initio study

The high pressure structural stability of thorium nitride (ThN) has been examined through first principle total energy calculations. The structural sequence predicted through present theoretical simulation is NaCl type structure (B1) to tetragonal phase (B10) to CsCl type (B2) phase with corresponding transition pressures ∼75 GPa and 120 GPa, respectively. The B1 → B10 transition with volume discontinuity of ∼10% is found to be of first order type, whereas, the B10 → B2 displays second order nature. The predicted high pressure structural sequence in ThN is different from those reported in earlier works [Gupta and Singh, Sol. State Sci., 2010 and Modak and Verma, Phys. Rev. B 2011]. The pressure induced phase transition sequence so obtained is further supported by examining the mechanical and phonon stability of the predicted structures in their structural stability regime. Also, the activation barrier for B1 to B10 transition determined from the calculated Bain path at the transition pressure turns out to be ∼0.75eV/f.u.(72.36 kJ/mol).

High-pressure structure prediction and high-temperature structural stability of periclase

Periclase is the terminal component of the ferropericlase, and its chemical composition is MgO. It is well known that there exists a huge difference between the melting curves of MgO determined experimentally and theoretically. A feasible way to clarify the nature of the melting temperature is to investigate the possible new phase of MgO. Meanwhile, it is very important to study the new phase and the influence of temperature on structural stability of MgO in high-pressure condensed matter physics and geophysics. In the present work, we study in detail the phase stability and the possible existing structures of MgO, which include the structure predicted by particle swarm optimization algorithm through using the first-principles pseudopotential density functional method. We find that MgO crystallizes into a rocksalt structure in a pressure range from 0 to 580 GPa and that the CsCl-type structure is of a high-pressure phase at up to 800 GPa. Although an NiAs-type hexagonal phase perhaps explains the volume discontinuity at (170 ± 10) GPa along the MgO Hugoniot in a shock-compression experiment (Zhang L, Fei Y W 2008 <i>Geophys. Res. Lett</i>. <b>35</b> L13302) and a wurtzite phase perhaps explains the huge difference between the melting curves of MgO determined experimentally and theoretically (Aguado A, Madden P A 2005 <i>Phys. Rev. Lett</i>. <b>94</b> 068501), neither of them is existent in the entire range of pressures studied, according to the thermodynamic stability calculations. The calculations of phonon spectra indicate that the B3, B4, B8<sub>1</sub>, B8<sub>2</sub>, and <i>P</i>3<i>m</i>1 phases of MgO are dynamically stable at zero pressure. That is to say, all of the predicted structures are the metastable structures of MgO. In addition, the high-temperature structural stability of MgO is investigated by using very similar Lewis-Catlow and Stoneham-Sangster shell model potential based on the classical molecular dynamics (MD) simulations. In order to take into account the non-central force in crystal, the breathing shell model is also introduced in simulation. The thermodynamic melting curves are estimated on the basis of the thermal instability MD simulations and compared with the available experimental data and other theoretical results in the pressure range of 0－150 GPa.

High pressure structural stability of the Na-Te system

The ab initio evolutionary algorithm is used to search for all thermodynamically stable Na-Te compounds at extreme pressure. In our calculations, several new structures are discovered at high pressure, namely, Imma Na2Te, Pmmm NaTe, Imma Na8Te2 and P4/mmm NaTe3. Like the known structures of Na2Te (Fm-3m, Pnma and P63/mmc), the Pmmm NaTe, Imma Na8Te2 and P4/mmm NaTe3 structures also show semiconductor properties with band-gap decreases when pressure increased. However, we find that the band-gap of Imma Na2Te structure increases with pressure. We presume that the result may be caused by the increasing of splitting between Te p states and Na s, Na p and Te d states. Furthermore, we think that the strong hybridization between Na p state and Te d state result in the band gap increasing with pressure.

Carbon nanohorns under cold compression to 40 GPa: Raman scattering and X-ray diffraction experiments

We report a high-pressure behavior of carbon nanohorns (CNHs) to 40 GPa at ambient temperature by in situ Raman spectroscopy and synchrotron radiation x-ray diffraction (XRD) in a diamond anvil cell. In Raman measurement, multiple structural transitions are observed. In particular, an additional band at ∼1540 cm−1 indicative of sp3 bonding is shown above 35 GPa, but it reverses upon releasing pressure, implying the formation of a metastable carbon phase having both sp2 and sp3 bonds. Raman frequencies of all bands (G, 2D, D + G, and 2D′) are dependent upon pressure with respective pressure coefficients, among which the value for the G band is as small as ∼2.65 cm−1 GPa−1 above 10 GPa, showing a superior high-pressure structural stability. Analysis based on mode Grüneisen parameter demonstrates the similarity of high-pressure behavior between CNHs and single-walled carbon nanotubes. Furthermore, the bulk modulus and Grüneisen parameter for the G band of CNHs are calculated to be ∼33.3 GPa and 0.1, respectively. In addition, XRD data demonstrate that the structure of post-graphite phase derives from surface nanohorns. Based on topological defects within conical graphene lattice, a reasonable transformation route from nanohorns to the post-graphite phase is proposed.

Hardness and compression behavior of niobium carbide

ABSTRACT We report the combined experimental and theoretical investigations on high pressure structural stability of niobium carbide (NbC). The compressibility of NbC has been measured using angle-dispersive synchrotron X-ray diffraction in a diamond anvil cell (DAC) at room temperature and high pressure (up to 38.0 GPa), complemented with first-principles density-function theory calculations. The results imply that NbC shows bulk modulus of = 281 (6) GPa with a pressure derivative = 6.2 (1.5) for its strong covalent bonding. In addition, indentation testing on the well-sintered bulk NbC obtained at 5.0 GPa/1400°C yielded a Vickers hardness of 19.2 GPa and fracture toughness of 7.7 MPa m1/2 at applied load of 10 kgf, demonstrating that binderless NbC prepared under high pressure should be a prospective hard material.

X-ray diffraction and spectroscopy study of nano-Eu2O3 structural transformation under high pressure

Nanoscale materials exhibit properties that are quite distinct from those of bulk materials because of their size restricted nature. Here, we investigated the high-pressure structural stability of cubic (C−type) nano-Eu2O3 using in situ synchrotron X−ray diffraction (XRD), Raman and luminescence spectroscopy, and impedance spectra techniques. Our high-pressure XRD experimental results revealed a pressure-induced structural phase transition in nano−Eu2O3 from the C−type phase (space group: Ia-3) to a hexagonal phase (A−type, space group: P-3m1). Our reported transition pressure (9.3 GPa) in nano-Eu2O3 is higher than that of the corresponding bulk-Eu2O3 (5.0 GPa), which is contrary to the preceding reported experimental result. After pressure release, the A−type phase of Eu2O3 transforms into a new monoclinic phase (B−type, space group: C2/m). Compared with bulk−Eu2O3, C-type and A-type nano−Eu2O3 exhibits a larger bulk modulus. Our Raman and luminescence findings and XRD data provide consistent evidence of a pressure-induced structural phase transition in nano-Eu2O3. To our knowledge, we have performed the first high-pressure impedance spectra investigation on nano-Eu2O3 to examine the effect of the structural phase transition on its transport properties. We propose that the resistance inflection exhibited at ∼12 GPa results from the phase boundary between the C−type and A−type phases. Besides, we summarized and discussed the structural evolution process by the phase diagram of lanthanide sesquioxides (Ln2O3) under high pressure.

Pressure induced phase transition and thermo-physical properties in LuX (X = N, P)

Detailed total energy calculations have been performed in lutetium pnictides (LuX, where X = N, P) to understand their high pressure structural stability. In LuN, the ambient rocksalt type structure (B1 phase) transforms to a tetragonal structure (B10 phase) at ∼240 GPa; whereas in LuP the orthorhombic structure (B33, space group Cmcm) emerges as a high pressure structure above 48 GPa. Both the transitions are found to be of first-order type with volume discontinuities of ∼6% and 8.2%, respectively. The high pressure phases B10 and B33 are found to be stable up to 400 GPa, respectively. Further, the structural stability predicted from static lattice calculations has been supported by lattice dynamical stability analysis. The present calculations rule out the B1 to B2 (CsCl type) structural phase transitions predicted to occur at 241 GPa in LuN and at 98 GPa in LuP by previous all-electron calculations (Gupta and Bhat 2013 J. Mol. Model 19 5343–54). The temperature dependence of several thermo-physical properties such as volume, bulk modulus, specific heat and thermal expansion coefficient of the rocksalt structure of these compounds calculated in the present study, using quasi-harmonic approximation, awaits confirmation by experimental studies.