Pressure-induced Amorphization Research Articles

Pressure-induced polyamorphism inTiO2nanoparticles

Two different nanometric (6 nm) ${\text{TiO}}_{2}$ compounds, anatase polycrystals and amorphous particles, were investigated under high pressure using Raman spectroscopy. Nanoanatase undergoes a pressure-induced amorphization. The pressure-induced transformations of this mechanically prepared amorphous state are compared with those of a chemically prepared amorphous particles. In the mechanically prepared amorphous state, a reversible transformation from a low-density amorphous state to high-density amorphous state (HDA1) is observed in the range 13--16 GPa. In the chemically prepared sample, a transformation to a new high-density amorphous state (HDA2) is observed at around 21 GPa. Further compression leads to the transformation $\text{HDA}2\ensuremath{\rightarrow}\text{HDA}1$ at $\ensuremath{\sim}30\text{ }\text{GPa}$. We demonstrate that depending on the starting amorphous material, the high-pressure polyamorphic transformations may differ. This observation indicates that pressure is a suited tool to discriminate between nanomaterials apparently similar at ambient conditions.

High pressure stability of bismuth sillenite: A Raman spectroscopic and x-ray diffraction study

High pressure behavior of the compound Bi12SiO20 is investigated using in situ Raman spectroscopic and synchrotron-based angle dispersive x-ray diffraction techniques. Results indicate that the compound remains stable in the ambient pressure cubic structure up to 26 GPa. From the structural studies, bulk modulus B0, and its pressure derivative B′ of Bi12SiO20 are evaluated to be 36 GPa and 16.7 GPa, respectively. Mode Grüneissen parameters of various Raman active modes of Bi12SiO20 are also reported. The stability of Bi12SiO20 at high pressure is discussed in the light of the pressure-induced amorphization reported in bismuth-orthosilicate (Bi4Si3O12) and -orthogermanate. Comparison of the observed phonon behavior with that reported for Bi4Si3O12 reveals that two of the Raman modes in Bi4Si3O12 have negative pressure dependencies clearly indicating dynamic instability while Bi12SiO20 does not show any signatures of zone-center instabilities.

Pressure-Induced Amorphization in Silicon Caused by the Impact of Electrosprayed Nanodroplets

This Letter describes the shock-induced amorphization of single-crystal Si bombarded by nanodroplets. At impact velocities of several kilometers per second, the projectiles trigger strong compression pulses lasting tens of picoseconds. The phase transition, confirmed via transmission electron microscopy and electron backscatter diffraction, takes place when the projectile's stagnation pressure is approximately 15GPa. We speculate that the amorphization results either from the decompression of the β-Sn phase or during the compression of the diamond phase.

Temperature dependence of the pressure-induced amorphization of iceIhstudied by high-pressure neutron diffraction to 30 K

High-pressure neutron diffraction allowed the in situ observation of the pressure-induced amorphization of ordinary ice ${I}_{h}$ between 130 and 30 K, i.e., to lower temperatures than any other diffraction study before. We find that the pressure required for complete transformation into high-density amorphous ice (HDA) increases with decreasing temperature to $\ensuremath{\sim}80\text{ }\text{K}$ but remains approximately constant below. Our findings support earlier evidence of two distinct mechanisms responsible for the pressure-induced amorphization in ice ${I}_{h}$, namely, amorphization due to mechanical melting down to lowest temperatures, and amorphization due to thermal melting at elevated temperatures. Such scenario naturally explains why HDA prepared through compression at 77 K is structurally distinct from the form of HDA obtained by the compression of low-density amorphous ice (LDA) and hence cannot be associated with the hypothesized high-density proxy of liquid water in a two-state model.

Absence of pressure-induced amorphization inLiKSO4

Angle-resolved synchrotron radiation diffraction was used to investigate lithium potassium sulfate(LiKSO4) crystals under high pressure. We confirm that the title compound undergoes three phasetransitions, and , observed at around 0.8 GPa, 4.0 GPa and 7.0 GPa, respectively. Two competitive structures are proposedfor the β-phase after powder diffraction data Rietveld refinements: an orthorhombic (space groupCmc 21) or a monoclinic(space group Cc) structure. These structures correspond to the models of the low temperature phases. Theγ-phase is indexed by a monoclinic structure. Finally, theδ-phase is found to be highly disordered. No evidence of any pressure-induced amorphousphase was observed up to 24 GPa, even under imposed highly non-hydrostatic conditions,contrary to previous propositions.

Deactivation of Pressure-Induced Amorphization in Silicalite SiO2 by Insertion of Guest Species

The incorporation of carbon dioxide or argon stabilizes the structure of the microporous silica polymorph silicalite well beyond the stability range of tetrahedrally coordinated SiO(2) and, in fact, beyond even the metastability range of low-pressure silica polymorphs such as quartz and cristobalite at room temperature. The bulk modulus of silicalite strongly increases as a result of the incorporation of CO(2) or Ar and is equivalent to that of quartz. The insertion of these species deactivates the normal compression and pressure-induced amorphization mechanisms in this material, impeding the softening of low-energy vibrations, amorphization, and the eventual increase in silicon coordination up to at least 25 GPa.

New description of structural disorder in silica glass. II. Application of atomistic energy distribution analysis to pressure effects

Molecular dynamics (MD) simulations have been made to study changes in density, oxygen coordination number and bond exchange during compression and decompression of quartz, cristobalite and silica glass. The interaction energies calculated by MD are analyzed in terms of ‘atomistic energy distribution (AED) with which pair-interaction energies are divided into equal halves allocated to each atom. Therefore, each atom has the summed-up value (‘atomistic potential energy’) of half the pair-interaction energies. The calculated results show different patterns and profiles in first and second moments of AED in the three silica systems, which are used to interpret pressure-induced amorphization of quartz, crystal-crystal transition in cristobalite and densification in silica glass. Making use of a previous AED analysis of thermal effects in silica glass [J. Non-Cryst. Solids. 355 (2009) 694], we finally compare and ascertain structural transformations that are due to either thermal or mechanical effects.

Amorphization of metal-organic framework MOF-5 at unusually low applied pressure

So far, amorphization of solid materials at ambient temperature required a high pressure (several gigapascal). This raises an important question: is it possible to induce amorphization of solid materials by a low pressure at ambient temperature? Herein, our x-ray diffraction measurements demonstrated that ${\text{Zn}}_{4}\text{O}{(\text{BDC})}_{3}$ metal-organic framework (MOF-5) can be irreversibly amorphized at ambient temperature by employing a low compressing pressure of 3.5 MPa, which is 100 times lower than that required for amorphization of other solids. This was further supported by the collapse of pores. Furthermore, the Raman spectra indicated that the irreversible pressure-induced amorphization (PIA) was due to the destroying of some carboxylate groups. One can conclude that the availability of thousands of MOFs can allow ones to reveal relationships between structures and PIA at a low pressure.

Photoluminescence and Raman Spectroscopy Studies of Eu(OH)3 Rods at High Pressures

Eu(OH)3 rods, with diameters of 140 nm and lengths of 100−500 nm were prepared by a hydrothermal method. X-ray diffraction indicated a pure hexagonal phase (space group P63/m) of the rods. The relations between structural and optical properties of Eu(OH)3 rods under high pressures were obtained by photoluminescence (PL) and Raman spectra. Two structural phase-transition points at around 4 and 8 GPa were observed in this work. When a pressure of about 4 GPa was applied to the samples, one new emission peak at 593 nm was observed in the PL spectra, indicating the splitting of the 7F1 Stark level in Eu3+ ions. Such a splitting was attributed to the decrease of site symmetry of Eu3+ ions from C3h to D2 at high pressures. Two new Raman bands appeared under a pressure up to about 8 GPa due to the pressure-induced amorphization. After the pressure was released, the original PL and Raman spectra were recovered.

Equation of state, phase stability, and amorphization ofSnI4at high pressure and temperature

We have measured the pressure-induced amorphization of tin iodide $({\text{SnI}}_{4})$ as a function of temperature and found a small $(<1\text{ }\text{GPa})$ increase in the initiation pressure of the transition from 293 to 523 K. We have also determined the $P\text{\ensuremath{-}}V$ equation of state while the material undergoes the amorphization, including multiple compressions of a single sample, using a diamond-anvil cell and x-ray diffraction. Apparent stiffening upon multiple compression of the sample can be explained by either an increase in nonhydrostaticity during loading or, possibly, changes in the initial crystal structure upon decompression recrystallization. Contrary to previous interpretations of the amorphization being a two-stage process, with ${\text{SnI}}_{4}$ converting to a second (unidentified) crystalline phase before the loss of Bragg intensities, the present experiments show that it is also possible to amorphize ${\text{SnI}}_{4}$ without the appearance of the second crystalline phase. While the new diffraction peaks appear upon the first compression of a sample, subsequent compressions of the same sample do not show these new peaks; instead, long-range ordering of the original cubic crystal structure is lost.

The role of vacancies in the pressure amorphisation phenomenon observed in Ge-Sb-Te phase change alloys

AbstractWe demonstrate, both experimentally and by computer simulation, that while the metastable face-centered cubic (fcc) phase of Ge-Sb-Te becomes amorphous under hydrostatic compression at about 15 GPa, the stable trigonal phase remains crystalline. We present evidences that the pressure-induced amorphisation phenomenon strongly depends on the concentration of vacancies included in the Ge/Sb sublattice, but is thermally insensitive. Upon higher compression, a body-centered cubic phase is obtained in both cases at around 30 GPa. Upon decompression, the amorphous phase is retained when starting with the fcc phase while the initial structure is recovered when starting with the trigonal phase. We argue that the presence of vacancies and the associated subsequent large atomic displacements lead to nanoscale phase separation and the loss of the initial structure memory in the fcc staring phase of Ge-Sb-Te. We futher compare the amorphous phase obtained via the pressure route with the melt quenched amorphous phase.

Pressure-Induced Amorphization and Polyamorphism in One-Dimensional Single-Crystal TiO2 Nanomaterials

The structural phase transitions of single-crystal TiO2−B nanoribbons were investigated in situ at high pressure using synchrotron X-ray diffraction and Raman scattering. Our results have shown a pressure-induced amorphization (PIA) occurred in TiO2−B nanoribbons upon compression, resulting in a high-density amorphous (HDA) form related to the baddeleyite structure. Upon decompression, the HDA form transforms to a low-density amorphous (LDA) form, while the samples still maintain their pristine nanoribbon shape. A high-resolution transmission electron microscopy (HRTEM) image reveals that the LDA phase has an α-PbO2 structure with short-range order. We propose a homogeneous nucleation mechanism to explain the pressure-induced amorphous phase transition in the TiO2−B nanoribbons. Our study demonstrates for the first time that PIA and polyamorphism occurred in the one-dimensional (1D) TiO2 nanomaterials and provides a new method for preparing 1D amorphous nanomaterials from crystalline nanomaterials.

Pressure-Induced Amorphization and Porosity Modification in a Metal−Organic Framework

The impact of modest, industrially accessible pressures (0-1.2 GPa) on the structure and porosity of the zeolitic imidazolate framework Zn(2-methylimidazole)(2), ZIF-8, was investigated using in situ powder X-ray diffraction in combination with sorption measurements for pressure-treated samples. The framework is highly compressible, with a bulk modulus (K = -V partial differential P/partial differential V) of 6.52(35) GPa, the most compressible metal-organic framework (MOF) documented to date. The framework undergoes an irreversible pressure-induced amorphization following compression beyond 0.34 GPa. The pressure-amorphized ZIF-8 remains porous, although the sorption characteristics are distinctly altered compared to the pristine material. As such, pressure can provide a new route to systematically modify the sorption behavior and other functional properties of MOFs, a nontraditional form of postsynthetic modification. Importantly, pressure modification of MOFs is effective at lower pressures than in other porous materials (e.g., zeolites) and, as such, is easily scalable and industrially relevant.

Pressure-induced transformations in crystalline and vitreous [formula omitted

Structural transitions in crystalline and vitreous PbGeO 3 were studied at pressures up to 20 GPa. Crystalline PbGeO 3 was observed to undergo a pressure-induced amorphization between 12–18 GPa. Vitreous PbGeO 3 was found to exhibit an amorphous-to-amorphous transition in a similar pressure range. The structural and thermal properties of the pressure-cycled PbGeO 3 materials were further studied with high-energy x-ray diffraction and differential scanning calorimetry. The properties were then compared to those of thermally quenched glass and ball-milled PbGeO 3 samples. The structure of pressure-amorphized PbGeO 3 was found to closely resemble that of ball-milled PbGeO 3. However, the thermal properties probed by differential scanning calorimetry exhibited significant differences to those of thermally quenched PbGeO 3 glass.

IR study of the pressure-induced amorphization and recrystallization of europium molybdate

Drastic changes of the IR spectra of optical phonons in europium molybdate single crystal were observed after its hydrostatic compression: instead of a series of narrow lines, wide bands were observed and a new band appeared, which can be attributed to the formation of the high pressure phase. Stepped annealing at temperatures from 100 to 550°C transformed the europium molybdate subjected to pressure to the initial β′ phase, the high-pressure phase disappeared, and bands corresponding to the α phase appeared.

Pressure-induced reversible amorphization in superconducting compound FeSe0.5Te0.5

We report pressure-induced amorphization phenomenon in a superconducting compound FeSe0.5Te0.5 to a pressure of 27 GPa in a diamond anvil cell. The synchrotron x-ray diffraction studies reveal that the ambient pressure tetragonal phase (space group P4/nmm) transforms to an amorphous phase at 11.5 GPa during compression and reverts back to the tetragonal phase during decompression at 2.8 GPa. The measured equation of state for the tetragonal phase and the amorphous phase is presented. The disordering of Fe(SeTe)4 tetrahedra under compression is attributed to a kinetic hindrance to a stable phase and is likely to impact its superconducting properties under high pressures.

High-pressure phase transformations, pressure-induced amorphization, and polyamorphic transition of the clathrateRb6.15Si46

The type-I clathrate ${\text{Rb}}_{6.15}{\text{Si}}_{46}$ with partly empty cage sites has been studied up to 36 GPa using Raman spectroscopy, synchrotron x-ray diffraction in diamond-anvil cells, and ab initio total-energy and lattice-dynamics calculations. A first phase transition is observed at $13\ifmmode\pm\else\textpm\fi{}1\text{ }\text{GPa}$ and a ``volume collapse'' transition within the clathrate structure is then observed at $24\ifmmode\pm\else\textpm\fi{}1\text{ }\text{GPa}$. Pressure-induced amorphization into a high-density amorphous (HDA) state occurs above $P=33\ifmmode\pm\else\textpm\fi{}1\text{ }\text{GPa}$. The HDA form transforms into a low-density amorphous polymorph during decompression. During the compression study using angle dispersive synchrotron x-ray diffraction techniques we measured bulk modulus parameters for rocksalt-structured TaO, included adventitiously in the clathrate sample [${K}_{0}=293(3)\text{ }\text{GPa}$ and ${K}_{0}^{\ensuremath{'}}=5.4(3)$].

Structural study of the Eu3+ environments in fluorozirconate glasses: Role of the temperature-induced and the pressure-induced phase transition processes in the development of a rare earth’s local structure model

The correlation between the optical properties of the Eu(3+) ions and their local structures in fluorozirconate glasses and glass-ceramics have been analyzed by means of steady-state and time-resolved site-selective laser spectroscopies. Changes in the crystal-field interaction, ranging from weak to medium strength values, are observed monitoring the luminescence and the lifetime of the Eu(3+) ions in different local environments in the glass. As key roles in this study, the Eu(3+) luminescence in the thermally-induced crystallization of the glass and the pressure-induced amorphization of the crystalline phase of the glass-ceramic experimentally states the existence of a parent local structure for the Eu(3+) ions in the glass, identified as the EuZrF(7) crystalline phase. Starting from the ab initio single overlap model, crystal-field calculations have been performed in the glass and the glass-ceramic. From the site-selective measurements, the crystal-field parameters sets are obtained, giving a suitable simulation of the (7)F(J) (J=0-6) Stark energy level diagram for the Eu(3+) ions in the different environments present in the fluorozirconate glass. A simple geometrical model based on a continuous distortion of the parent structure is proposed for the distribution of local environments of the Eu(3+) ions in the fluorozirconate glass.

Presentation of the Mineralogical Society of America Award for 2008 to James Badro

President Heaney, MSA Members, and guests: It is with great pleasure that I introduce you to the recipient of the Mineralogical Society of America Award for 2008, Jimi Badro. James Badro started with a physics background (B.S., M.S., Ph.D.) at Ecole Normale Superieure de Lyon. At that time, Professors Philippe Gillet and Francis Albarede ran a very successful outreach program called “Geophysics and Geochemistry for Physicists,” that converted Jimi to a mineral physicist. James wrote a series of papers establishing the theoretical basis for the new expanding field of pressure-induced mineral amorphization, including the prediction of fivefold-coordinated silica intermediate phase and the interpretation of memory glass. He also reported strong-to-fragile transition in silica melts and solubility of argon in silicate melts. He collaborated with our group on a high-pressure, XRD, and X-ray imaging experiment that became a cornerstone in advancing ultrahigh-pressure diamond-anvil technique over three megabars. James was one of the very few scientists who had made outstanding contributions in both theoretical and experimental mineral physics, and he had done these before his Ph.D. degree. After receiving Ph.D. degree, Jimi was facing the draft to French military service with an option. In the French system, …

A study of the pressure-induced reversible amorphization of Xe containing-LTA zeolites by energy minimization technique

A previous computational study on dehydrated LTA zeolites [J. Gulín-González, G.B. Suffritti, Micropor. Mesopor. Mater . 69 (2004) 127] suggested the reversible amorphization of calcined LTA samples at pressures below 6 GPa, in agreement with the experimental results. However, the effect of guest molecules on the amorphization process was not evaluated in that study. In this paper, the potential reversible amorphization of Xe containing-LTA samples under high external pressures is studied via energy minimization calculations. The results of the simulations confirmed the pressure-induced amorphization of LTA zeolites at pressures about 2–4 GPa for all the studied samples. Besides, the simulations stressed the importance of the structural topology, particularly of D4R secondary units, for the recovering of the crystalline order. According to our calculations the exchangeable cations (Na + and Li +) play a crucial role in the process of amorphization. Our results suggest that the reversible amorphization is essentially independent on the presence of Xe molecules in the range of the pressures studied ( P ⩽ 6 GPa).