High-pressure Structural Evolution Research Articles

Pressure-induced phase transition in cubic Yb2O3 and phase transition enthalpies

The high pressure structural evolution of cubic Yb2O3 has been studied using in situ synchrotron angle dispersive x-ray diffraction in combination with diamond anvil cell techniques up to 44.1 GPa. The XRD measurements revealed an irreversible reconstructive phase transition from cubic to monoclinic Yb2O3 at 11.2 GPa and extending up to 28.1 GPa with ∼8.1% volume collapse and a subsequent reversible displacive transition from monoclinic to hexagonal phase starting at 22.7 GPa. The monoclinic phase coexists with the hexagonal phase up to 44.1 GPa. After pressure releases, the hexagonal Yb2O3 reverts to the monoclinic structure. The second-order Birch–Murnaghan equation of state fit to the pressure–volume data yields a bulk modulus of 201 (4), 187 (6), and 200 (4) GPa for the cubic, monoclinic, and hexagonal phases, respectively. Furthermore, the effects of the hydrostatic pressure state on the diffraction patterns, bulk modulus, and onset transition pressure of Yb2O3 under high pressure have been discussed. It is concluded that the bulk modulus of the cubic Ln2O3 phase increases with decreasing cation radius due to lanthanide contraction. Another important work in this study is the determination of the enthalpies of the cubic to monoclinic and monoclinic to hexagonal phase transitions of Yb2O3 of 37.0 and 17.4 kJ/mol, respectively, based on the basic thermodynamic equations and using the onset transition pressures and corresponding volume changes obtained from high pressure XRD experiments.

Structure evolution of fluorapophyllite-(K) under high pressure

ABSTRACT The high pressure structural evolution of a natural fluorapophyllite-(K) K0.70(NH4)0.20 Ca3.97Na0.07[Al0.04Si7.96O20]F0.99·(H2O)8.05, Z = 2, a = 8.9757(2), c = 15.7920(2) Å, space group P4/mnc, from Nidym river, East Siberia, Russia, compressed in penetrating (ethanol:water 4:1 mixture) and non-penetrating (paraffin oil) media up to 4.7 GPa, was studied by single-crystal X-ray diffraction with a diamond anvil cell. The compressibility is identical in both media. At the initial stage the compression proceeds mainly within the plane (xy) and less along the z-axis; above 3 GPa the compression becomes almost isometric. Within the whole pressure range there are no signs of the symmetry lowering. The main pressure-induced effect on the tetrahedral layer consists in a cooperative rotation of the 4-fold rings, which provides the structure compression within the (xy) plane. The compression along the z-axis proceeds through the shortening of the interlayer distance, whereas the thickness of silicate layer remains almost unchanged.

Phase transition of potassium sodium niobate under high pressures

As a piezoelectric material, K0.5Na0.5NbO3 (KNN) has broad application prospects in ultrasonic transducers, sensors, and biomedicine areas. Its structure information under high pressures is of great significance for guiding device design. In this study, the high-pressure structural evolution of KNN has been studied. Two structural phase transitions were revealed by high-pressure Raman spectrum. The phase transition boundary was found by Raman vibration mode analysis, with transformation ranges of 2.5–4.6 and 6.8–9.4 GPa. The phase structures were determined by in situ neutron diffraction, with a phase transformation path of orthogonal Amm2 (O) → tetragonal P4mm (T) → cubic Pm3¯m (C) structure at high pressures. Synchrotron x-ray diffraction further confirmed the phase transformation path. During the processes of phase transitions, the path of Nb atom was clearly described as moving toward [1¯01] and then [100] direction. An output power density of KNN ceramic devices was comparable to that of commercially available PZT 95/5. The density of KNN ceramic is approximately half that of PZT 95/5, which means a significant advantage in terms of weight reduction and miniaturization of equipment in global demand. The phase transition of ferroelectric materials under high pressures provides scientific guidance for the development of high-power pulse power devices.

A pressure-induced high-pressure metallic GeTe phase.

As an important phase-change material, GeTe has many high-pressure phases as well, but its phase transitions under pressure are still lack of clarity. It is challenging to identify high-pressure GeTe crystal structures owing to the phase coexistence in a wide pressure range and the reversibility of phase transitions. Hence, first-principles calculations are required to provide further information in addition to limited experimental characterizations. In this work, a new orthorhombic Cmca GeTe high-pressure phase has been predicted via the CALYPSO method as the most energetically favorable phase in the pressure range between ∼30 and ∼38.5GPa, which would update the GeTe high-pressure phase transition sequence. The crystal structure of the Cmca phase is composed of alternate stacking puckered layers of Ge six-membered rings and Te four-membered rings along the b direction. The high density of states near the Fermi level and delocalization of electrons from the two-dimensional electron localization function indicate a strong metallic property of the Cmca phase. Electron-phonon coupling calculations indicate that the Cmca phase is superconductive below ∼4.2K at 35GPa. The simulated x-ray diffraction pattern of the Cmca phase implies that this phase might coexist with the Pnma-boat phase under high pressure. These results offer further understanding on the high-pressure structural evolution and physical properties in GeTe and other IV-VI semiconductors.

The high-pressure structural evolution of ErVO4 investigated by photoluminescence spectroscopy

• The high pressure photoluminescence spectra of ErVO 4 were collected up to ∼ 35 GPa. • The changes of photoluminescence spectra indicate the existence of three phase transitions upon compression. • ErVO 4 experiences zircon to scheelite to fergusonite to post-fergusonite phase transition sequences. • Scheelite-type ErVO 4 is recovered after pressure release. The phase stability of ErVO 4 was investigated by photoluminescence spectroscopy up to ∼ 35 GPa. The changes in spectra at ∼ 7.9 GPa, ∼20 GPa and ∼ 31 GPa suggest the existence of three phase transitions upon compression. With comparison to related rare earth orthovanadates, we suggested ErVO 4 experiences zircon to scheelite to fergusonite to orthorhombic Cmca phase transition sequences. Our study provides the photoluminescence signature for various polymorphs of ErVO 4 , which will refine our understanding of the structural behavior of rare earth orthovanadates.

High-Pressure Structural Evolution of Disordered Polymeric CS2.

Carbon disulfide is an archetypal double-bonded molecule belonging to the class of group IV-group VI, AB2 compounds. It is widely believed that, upon compression to several GPa at room temperature and above, a polymeric chain of type (-(C═S)-S-)n, named Bridgman's black polymer, will form. By combining optical spectroscopy and synchrotron X-ray diffraction data with ab initio simulations, we demonstrate that the structure of this polymer is different. Solid molecular CS2 polymerizes at ∼10-11 GPa. The polymer is disordered and consists of a mixture of 3-fold (C3) and 4-fold (C4) coordinated carbon atoms with some C═C double bonds. The C4/C3 ratio continuously increases upon further compression to 40 GPa. Upon decompression, structural changes are partially reverted, while the sample also undergoes partial disproportionation. Our work uncovers the nontrivial high-pressure structural evolution in one of the simplest molecular systems exhibiting molecular as well as polymeric phases.

High pressure structural evolution of cubic solid solution YbInO3

The structural evolution of cubic (c) solid solution YbInO3 (space group Ia3¯) under pressure has been investigated using synchrotron based angle dispersive x-ray diffraction measurements and density functional theory based first principles calculations. A first order irreversible structural phase transition is observed at ∼15 GPa. The ambient cubic phase coexists with the high pressure phase up to the highest pressure achieved in the experiment, i.e., 42 GPa. Based on experimental and theoretical investigations, the high pressure phase of c-YbInO3 is proposed to be an orthorhombic solid solution structure having the space group Pnma. In the high pressure Pnma phase, the coordination of Yb1/In1 (general site 4c) atoms with respect to O atoms increases from six to eight, while Yb2/In2 (special site 4b) atoms remain in six coordination. Our theoretical calculations show that distorted octahedra (YbO6 and InO6), sitting at the general position in c-YbInO3, change its geometry toward regular octahedra with increasing pressure, which gives rise to the phase transformation.

Probing High-Pressure Structural Evolution in Polyurea with In Situ Energy-Dispersive X-ray Diffraction and Molecular Dynamics Simulations

Polyurea, an elastomer with a phase-segregated microstructure, has been proven as an effective coating in defense applications. To gain a more complete understanding of the high-pressure atomic-level morphology of these phases and to validate molecular dynamics (MD) simulations, multi-angle energy-dispersive X-ray diffraction experiments were performed in situ up to pressures of ∼6 GPa at room temperature. Structure factors were obtained and compared to MD simulations with an average error of less than 5% between major peak positions. The first sharp diffraction peak shifted from 4.56 Å to lower d-spacing with pressure, indicating compression between hard segments. This was further supported by the behavior of a peak at ∼3.86 Å from the pair distribution function (PDF), suspected to represent π-stacking and separation between soft segments. Compression within the hard segments themselves is minimal as low-r peaks in the PDF are not greatly affected by pressure.

The High-Pressure Structural Evolution of Olivine along the Forsterite–Fayalite Join

Structural refinements from single-crystal X-ray diffraction data are reported for olivine with a composition of Fo100 (forsterite Mg2SiO4, synthetic), Fo80 and Fo62 (~Mg1.6Fe0.4SiO4 and ~Mg1.24Fe0.76SiO4, both natural) at room temperature and high pressure to ~8 GPa. The new results, along with data from the literature on Fo0 (fayalite Fe2SiO4), were used to investigate the previously reported structural mechanisms which caused small variations of olivine bulk modulus with increasing Fe content. For all the investigated compositions, the M2 crystallographic site, with its bonding configuration and its larger polyhedral volume, was observed to control the compression mechanisms in olivine. From Fo100 to Fo0, the compression rates for M2–O and M1–O bond lengths were observed to control the relative polyhedral volumes, resulting in a less-compressible M1O6 polyhedral volume, likely causing the slight increase in bulk modulus with increasing Fe content.

High-Pressure Evolution of Crystal Bonding Structures and Properties of FeOOH.

Recent conflicting reports on the high-pressure structural evolution of iron oxide-hydroxide (FeOOH) offer starkly contrasting scenarios for the hydrogen and oxygen cycles in Earth's interior. Here we explore the crystal structures of FeOOH using an advanced search algorithm combined with first-principles calculations. Our results indicate a phase transition around 70 GPa from the known ε-FeOOH to a new pyrite-type FeOOH (P-FeOOH) phase, and the two phases remain nearly degenerate in an unusually large pressure range. These findings clarify and explain the experimentally observed structural evolution and extensive phase coexistence. Moreover, our structure search identifies a previously unknown monoclinic (M-FeOOH) phase that is energetically close to P-FeOOH at pressures near the core-mantle boundary. We further reveal that the high-pressure FeOOH phases exhibit remarkably distinct sound-velocity profiles, providing key material properties essential to interpreting seismic data and elucidating FeOOH's influence on geophysical and geochemical processes in deep Earth.

Structural and electronic properties of MnSi under high pressure: A first-principles calculation

To explore the structure and phase stabilities of transition metal silicides under high pressure, we report a systematic study of the high-pressure structural evolution of MnSi using the CALYPSO structure searching method and first-principles calculations. A novel cubic Pm-3m-structured MnSi with a MnSi8 cube environment is uncovered. Upon increasing the pressure to 41.91GPa, the cubic ε-FeSi-type MnSi transforms into a CsCl structure. Both the ε-FeSi and CsCl phases are shown to be mechanically and dynamically stable. The density of states, electron localization function and Bader charge analysis suggest that both phases of MnSi possess dominant covalent bonding character.

Experimental and theoretical investigation on the compression mechanism of FeF3 up to 62.0 GPa.

VF3-type FeF3 is generally considered as a perovskite with a completely vacant A site. The high-pressure structural evolution of FeF3 has been studied by both X-ray diffraction and theoretical simulation up to 62.0 GPa. Experimental and theoretical results demonstrate that VF3-type FeF3 is stable up to 50 GPa. The structural evolution presents three features at different pressure ranges. At P < 10 GPa, the volume reduction is dominated by the FeF6 octahedral rotation, and a small octahedral strain develops upon compression, which represents an elongation of FeF6 octahedra along the c axis. Between 10 and 25 GPa, the volume reduction is mainly attributed to the Fe-F bond length decreasing, and the octahedral strain gradually disappears. Between 25 and 50 GPa, an octahedral elongation along the a axis quickly develops, resulting in a substantial structural distortion. Structural instability is predicted at P > 51 GPa on the basis of a soft mode occurring in phonon calculations. The pressure-volume relationship is described by a third-order Birch-Murnaghan equation-of-state with B0 = 14 (1) GPa, B0' = 17 (1) by experiment and B0 = 10.45 (1) GPa, B'10 = 12.13 (1) by calculation.

Unraveling Convoluted Structural Transitions in SnTe at High Pressure

The longstanding uncertainty in high-pressure structural evolution of SnTe has greatly impeded the understanding of its complex electronic properties. Here we unravel the convoluted high-pressure phase transitions of SnTe using angle-dispersive synchrotron X-ray diffraction combined with first-principles structural search. We identify three coexisting intermediate phases of Pnma, Cmcm, and GeS type structure and establish the corresponding phase boundaries. We further unveil the intricate pressure-driven evolution of the energetics, kinetics, and lattice dynamics to elucidate its distinct phase-transition mechanisms. These findings resolve structures of SnTe, which have broad implications for other IV–VI semiconductors that likely harbor similar novel high-pressure phases.

First-principles investigation on high-pressure structural evolution of MnTiO3

First-principle calculations using density-functional theory with linearized augmented plane wave method and projector-augmented method have been performed for the high-pressure MnTiO3 polymorphs and their possible dissociation products. Theoretical results demonstrate that ilmenite-type MnTiO3 transforms into perovskite phase at 27GPa and 0K. The lithium niobate phase of MnTiO3 is confirmed to be metastable according to its higher Gibbs free energy compared with that of ilmenite at ambient conditions. In ilmenite and lithium niobate phases, MnO6 octahedra become more distorted while TiO6 octahedra become more regular with increasing pressure. In orthorhombic perovskite phase, the structural distortion deviated from the ideal cubic perovskite is enhanced at higher pressure. Based on the non-spin-polarized calculations, perovskite phase MnTiO3 is predicted to dissociate into Fm3̄m-MnO+P21/c-MnTi2O5 at 29GPa.

Structural evolution of hemimorphite at high pressure up to 4.2 GPa

The high-pressure structural evolution of hemimorphite, Zn4Si2O7(OH)2·H2O, a = 8.3881(13), b = 10.7179(11), c = 5.1311(9) A, V = 461.30(12) A3, space group Imm2, Z = 2, was studied by single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions up to 4.2 GPa. In the pressure range of 0.0001–2.44 GPa, the unit-cell parameters change almost linearly. The phase transition (probably of the second order) with symmetry reduction from Imm2 (hemimorphite-I) to Pnn2 (hemimorphite-II) was found near 2.5 GPa. The structure compressibility increases somewhat above the phase transition. Namely, the initial unit-cell volume decreases by 3.6% at 2.44 GPa and by 7.2% at 4.20 GPa. The hemimorphite framework can be described as built up of secondary building units (SBU) Zn4Si2O7(OH)2. These blocks are combined to form the rods arranged along the c-axis; these rods are multiplied by basic and I-translations of orthorhombic unit cell. The symmetry reduction is caused by the rotation of the rods along their axis. In hemimorphite-I, the compression affects mainly the SBU dimensions, whereas a rectangular section of the channels having mm2 symmetry remains practically unchanged. An appreciable decrease in this section in hemimorphite-II is determined by its oblique distortion with the loss of m planes. It results from opposite rotation of adjacent SBU, which also leads into the loss of I-translation. In hemimorphite-I, the coordination of H2O molecules is fourfold planar; the hydrogen-bonded hydroxyls and H2O molecules form infinite ribbons along the c-axis. In hemimorphite-II, an additional short H2O–O contact appears as a result of asymmetric deformation of the channels. The appearance of this new contact provides the possibility for re-orientation of hydrogen bonds. The planar coordination of H2O molecules changes to tetrahedral and the ribbons are transformed to islands (OH)2–H2O.

High-pressure structural evolution and equation of state of analbite

The volume and unit-cell parameters of analbite (i.e., NaAlSi 3 O 8 with complete Al,Si disorder) have been determined by single-crystal X-ray diffraction to a maximum pressure of ~8.71 GPa. The volume variation with pressure is described by a fourth-order Birch-Murnaghan equation of state with K 0T = 50.3(5) GPa, K 0 ′ = 8.9(5), and K 0 ″ = −2.4(3) GPa −1 . The value of the room-pressure bulk modulus is ~4% lower than that of low albite, and the onset of volume softening in analbite is at ~6.7 GPa, some 1.7 GPa higher than the onset in albite. The anisotropy of compression of analbite is less than that in albite. Single-crystal structure determinations of analbite to ~9.4 GPa show that there is no significant detectable compression of the T-O bonds within the structure, and the compression of the framework of tetrahedra is therefore accommodated by changes in the T-O-T angles, which result in significant compression of the “crankshaft chains” within the framework. No significant shear of the tetrahedral rings of analbite was detected, in contrast to the structural compression of albite. Overall, the structural changes that occur in analbite from 0.0001 to 9.4 GPa resemble those seen in ordered albite over the pressure range 0.0001–4 GPa. Therefore analbite shows a significantly greater structural rigidity than low albite up to pressures of 9.4 GPa.

Structural evolution of a 3T phengite mica up to 10 GPa: an in-situ single-crystal X-ray diffraction study

Abstract The high-pressure structural evolution of a natural 3T-phengite [(K0.90Na0.05)S = 0.95(Al1.51Mg0.32Fe0.18Ti0.03)S = 2.04(Si3.40Al0.60)O10(OH)2, a = b = 5.2279(11) and c = 29.752(7) Å, space group: P3112] from Cima Pal (Sesia Zone, Western Alps, Italy) was studied by single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions up to about 10 GPa. Nine structural refinements were performed at selected pressures within the P-range investigated. The compressional behavior of the same phengite sample was previously studied up to about 27 GPa by synchrotron X-ray powder diffraction, and the corresponding P–V curve was modeled by a third-order Birch–Murnaghan Equation of State (BM-EoS). The significant elastic anisotropy of the 3T-phengite (i.e. β(c) &gt; β(a)) is mainly controlled by the compression of the K-polyhedra. The evolution of the volume of the inter-layer K-polyhedron as a function of P is monotonic, without any evidence of discontinuity. Fitting the P–V data with a truncated second-order BM-EoS, we obtain a bulk modulus value of K 0(K-polyhedron) = 35(3) GPa. The tetrahedra and octahedra in the 3T-phengite structure are significantly less compressible than the K-polyhedron, and behave similarly to rigid units within the P-range investigated. The main P-induced effect on the tetrahedral sheet consists in a cooperative rotation of the tetrahedra, describable by the evolution of the “tetrahedral rotation angle” (or “ditrigonal rotation angle”, α) as a function of P. The value of the ditrigonal rotation angle increases significantly with P: α (°) = α P0 + 0.57(2)P (GPa) [R about 99%]. The volume of the K-polyhedron and the value of ditrigonal rotation parameter (α) are not independent of one another, showing a correlation of about 99%.

Pressure-induced structural deformation and elastic behavior of wairakite

The elastic behavior and the high-pressure structural evolution of the zeolite wairakite [ideal chemical formula Ca(Al 2 Si 4 O 12 )⋅2H 2 O, space group I2/a], the Ca-analog of analcime, have been investigated by means of in-situ synchrotron X-ray powder diffraction from ambient pressure to 7.8 GPa, and upon decompression. No complete X-ray amorphization is observed up to the highest investigated pressure, and the original unit-cell parameters are recovered upon decompression. The Rietveld structural refinements of the powder patterns converged successfully up to 2.5 GPa; above this pressure, a phase transition to triclinic symmetry is observed and only the unit-cell parameters were refined. An overall reduction of about 14% of the unit-cell volume between 0.0001 and 7.0 GPa is observed, demonstrating that wairakite is much more flexible upon compression than upon heating. The pressure dependence of the cell parameters is strongly anisotropic and larger after the transition to the triclinic space group. The elastic parameters refined with a second-order Birch-Murnaghan Equation of State are V 0 = 2536(4) Å 3 , K 0 = 39(3) GPa, and V 0 = 2632(38) Å 3 , K 0 = 24(3) GPa, for the monoclinic and triclinic phases, respectively. The structure distortion of monoclinic wairakite, proceeding via tetrahedral tilting, induces deformations in the 4-, 6-, and 8-membered rings and an increase in the extra-framework Ca coordination number. A comparative discussion of the compressibility behavior of wairakite and analcime is reported.

Elastic behaviour and structural evolution of topaz at high pressure

The elastic behaviour and the high-pressure structural evolution of a natural topaz, Al2.00Si1.05O4.00(OH0.26F1.75), have been investigated by means of in situ single-crystal X-ray diffraction up to 10.55(5) GPa. No phase transition has been observed within the pressure range investigated. Unit-cell volume data were fitted with a third-order Birch-Murnaghan Equation of State (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are: V0=345.57(7) A3, KT0=164(2) GPa and K′=2.9(4). The axial-EoS parameters are: a0=4.6634(3) A, KT0(a)=152(2) GPa, K′(a)=2.8(4) for the a-axis; b0=8.8349(5) A, KT0(b)=224(3) GPa, K′(b)=2.6(6) for the b-axis; c0=8.3875(7) A, KT0(c)=137(2) GPa, K′(c)=2.9(4) for the c-axis. The magnitude and the orientation of the principal Lagrangian unit-strain ellipsoid were determined. At P−P0=10.55 GPa, the ratios e1:e2:e3 are 1.00:1.42:1.56 (with e1||b, e2||a, e3||c and |e3| > |e2| > |e1|). Four structural refinements, performed at 0.0001, 3.14(5), 5.79(5) and 8.39(5) GPa describe the structural evolution in terms of polyhedral distortions.

Anomalous elastic behavior and high-pressure structural evolution of zeolite levyne

Elastic behavior and high-pressure (HP) structural evolution of a natural zeolite levyne, (Ca 0.5 ,Na,K) 6 (Al 6 Si 12 O 36 )·18H 2 O, has been investigated up to 5 GPa by means of in situ single-crystal X-ray diffraction with a diamond-anvil cell using a non-penetrating pressure-transmitting medium. Peculiar elastic behavior has been observed in the range 0–1 GPa: the c parameter decreases between 0 and 0.2 GPa, then increases up to 0.5–0.6 GPa. Above this P -value, the parameter decreases as expected. Anomalous behavior is also shown by the a -parameter, which first increases up to 0.2 GPa, then decreases as expected. However, these anomalous lattice variations are only slightly reflected in the cell volume behavior. The low- P trend ( P P > 1 GPa, refined with a second-order Birch-Murnaghan EoS, yields the following parameters: V 0 = 3539(3) A 3 and K T 0 = 48(1) GPa. Comparison of structural refinements performed at 0.0001, 0.79(5), and 3.00(5) GPa highlights two distinct deformation mechanisms of the Si/Al-framework, one predominant at low pressures (0–1 GPa) and the other at high pressures (1–5 GPa). The extra-framework content does not show any evident modification within the pressure range investigated.