Large Volume Collapse Research Articles

A Novel High-Density Phase and Amorphization of Nitrogen-Rich 1H-Tetrazole (CH2N4) under High Pressure

The high-pressure behaviors of nitrogen-rich 1H-tetrazole (CH2N4) have been investigated by in situ synchrotron X-ray diffraction (XRD) and Raman scattering up to 75 GPa. A first crystalline-to-crystalline phase transition is observed and identified above ~3 GPa with a large volume collapse (∼18% at 4.4 GPa) from phase I to phase II. The new phase II forms a dimer-like structure, belonging to P1 space group. Then, a crystalline-to-amorphous phase transition takes place over a large pressure range of 13.8 to 50 GPa, which is accompanied by an interphase region approaching paracrystalline state. When decompression from 75 GPa to ambient conditions, the final product keeps an irreversible amorphous state. Our ultraviolet (UV) absorption spectrum suggests the final product exhibits an increase in molecular conjugation.

Polymorphism in Strontium Tungstate SrWO4 under Quasi-Hydrostatic Compression.

The structural and vibrational properties of SrWO4 have been studied experimentally up to 27 and 46 GPa, respectively, by angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy measurements as well as using ab initio calculations. The existence of four polymorphs upon quasi-hydrostatic compression is reported. The three phase transitions were found at 11.5, 19.0, and 39.5 GPa. The ambient-pressure SrWO4 tetragonal scheelite-type structure (S.G. I41/a) undergoes a transition to a monoclinic fergusonite-type structure (S.G. I2/a) at 11.5 GPa with a 1.5% volume decrease. Subsequently, at 19.0 GPa, another structural transformation takes place. Our calculations indicate two possible post-fergusonite phases, one monoclinic and the other orthorhombic. In the diffraction experiments, we observed the theoretically predicted monoclinic LaTaO4-type phase coexisting with the fergusonite-type phase up to 27 GPa. The coexistence of the two phases and the large volume collapse at the transition confirm a kinetic hindrance typical of first-order phase transitions. Significant changes in Raman spectra suggest a third pressure-induced transition at 39.5 GPa. The conclusions extracted from the experiments are complemented and supported by ab initio calculations. Our data provides insight into the structural mechanism of the first transition, with the formation of two additional W-O contacts. The fergusonite-type phase can be therefore considered as a structural bridge between the scheelite structure, composed of [WO4] tetrahedra, and the new higher pressure phases, which contain [WO6] octahedra. All the observed phases are compatible with the high-pressure structural systematics predicted for ABO4 compounds using crystal-chemistry arguments such as the diagram proposed by Bastide.

Pressure-induced structural transformation of CaC2

The high pressure structural changes of calcium carbide CaC2 have been investigated with Raman spectroscopy and synchrotron X-ray diffraction (XRD) techniques in a diamond anvil cell at room temperature. At ambient conditions, two forms of CaC2 co-exist. Above 4.9 GPa, monoclinic CaC2-ii diminished indicating the structural phase transition from CaC2-ii to CaC2-i. At about 7.0 GPa, both XRD patterns and Raman spectra confirmed that CaC2-i transforms into a metallic Cmcm structure which contains polymeric carbon chains. Along with the phase transition, the isolated C2 dumbbells are polymerized into zigzag chains resulting in a large volume collapse with 22.4%. Above 30.0 GPa, the XRD patterns of CaC2 become featureless and remain featureless upon decompression, suggesting an irreversible amorphization of CaC2.

High pressure structural, electronic, and optical properties of polymorphic InVO4 phases

In the present work, we report a detailed density functional theory calculation on polymorphic InVO4 phases by means of projector augmented wave method. The computed first-order structural phase transformation from orthorhombic (Cmcm) to monoclinic (P2/c) structure is found to occur around 5.6 GPa along with a large volume collapse of 16.6%, which is consistent with previously reported experimental data. This transformation also leads to an increase in the coordination number of vanadium atom from 4 to 6. The computed equilibrium and high pressure structural properties of both InVO4 phases, including unit cell parameters, equation of state, and bulk moduli, are in good agreement with the available experimental data. In addition, compressibility is found to be highly anisotropic and the b-axis being more compressible than the other for both the structures. Electronic band structures for both the phases were calculated, and the band gaps for orthorhombic and monoclinic InVO4 are found to be 4.02 and 1.67 eV, respectively, within the Tran-Blaha Modified Becke-Johnson potential as implemented in linearized augmented planewave method. We further examined the optical properties such as dielectric function, refractive index, and absorption spectra for both the structures. From the implications of these results, it can be proposed that the high pressure InVO4 phase can be more useful than orthorhombic phase for photo catalytic applications.

Pb・Biを含むペロブスカイト型酸化物の高圧合成と構造，物性

Pb- and Bi- containing perovskites exhibit exotic properties owing to the presence of 6s electrons. High-pressure technique is promising method for synthesizing a wide variety of the perovskites. In this paper, the exotic properties of Pb- or Bi- containing perovskites, such as the origin of a large tetragonal distortion in PbVO3, structural transformation of PbMnO3 under high pressure, a large volume collapse accompanied with spin state transition in BiCoO3, polarization rotation in BiCo1−xFexO3 solid solution, and negative thermal expansion in BiNiO3 based materials are demonstrated. These properties are attributed to the correlation between 6s orbital of Pb and Bi and 3d orbital of transition metal elements.

High-pressure polymorphism as a step towards high density structures of LiAlH4

Two high density structures β- and γ-LiAlH4 are detected in LiAlH4, a promising hydrogen storage compound, upon compression in diamond anvil cells, investigated with synchrotron X-ray diffraction and first-principle calculations. The joint of the experimental and theoretical results has confirmed the sequence of the pressure-induced structural phase transitions from α-LiAlH4 (space group P21/c) to β-LiAlH4 (P21/c-6C symmetry), and then to γ-LiAlH4 (space group Pnc2), which are not reported in previous literatures. At the α to β transition point for LiAlH4, the estimated difference in cell volume is about 20%, while the transformation from β to γ phase is with a volume drop smaller than 1%. The α to β phase transition is accompanied by the local structure change from a AlH4 tetrahedron into a AlH6 octahedron, which contributes to a large volume collapse.

Pressure-Induced Reversible Phase Transformation in Nanostructured Bi2Te3 with Reduced Transition Pressure

High-pressure research on nanostructured materials has been of considerable interest owing to the quantum confinement effect and intrinsic defects in the nanocrystals. Here, we report a pressure-induced reversible structural phase transition in nanostructured Bi2Te3 hierarchical architectures (HAs) that were prepared via a facile solution-phase method. Therein, distinct phases I–IV by respectively adopting crystal structures of rhombohedral (I), monoclinic (II, III), and cubic (IV) were experimentally identified with increasing pressure up to 20.2 GPa in a diamond anvil cell (DAC). It is worthwhile to notice that nanostructured Bi2Te3 HAs ultimately evolved into a fascinating Bi–Te substitutional nonmetallic alloy at pressure even as low as 15.0 GPa, approximately 10 GPa lower than that of the corresponding bulk counterpart. The synergistic effect involving large volume collapse and the unique one-dimensional nanostructures with intrinsic antisite defects was proposed to be responsible for the reduction of transition pressure that is contrary to the general model for most nanomaterials. Our findings may pave a potential pathway for developing future multifunctional nanoalloys that are composed of nonmetallic elements.

Pressure-Induced Valence Change and Semiconductor–Metal Transition in PbCrO3

Pressure-induced valence change and semiconductor–metal transition were revealed in perovskite compound PbCrO3 by X-ray absorption spectroscopy (XAS) and resistance measurements, respectively. The Cr L2,3 edge XAS spectra indicate a charge disproportionation of Cr (3Cr4+ → 2Cr3+ + Cr6+) at ambient pressure, suggesting that the ambient-pressure phase of PbCrO3 has complex local structure and cannot be explained using the simple cubic perovskite structure (Pm-3m). Upon compression up to 4.2 GPa, Cr3+ and Cr6+ ions were converted to Cr4+ via charge transfer, associated with semiconductor–metal transition. The high-pressure metal phase is determined to be cubic perovskite structure (Pm-3m). Compared with the previous X-ray diffraction experiment, the large volume collapse (∼9.8% at 1.6 GPa) may be related to valence change and semiconductor–metal transition.

In situ high-pressure synchrotron X-ray diffraction study of the structural stability in NdVO4 and LaVO4

Room-temperature angle-dispersive X-ray diffraction measurements on zircon-type NdVO4 and monazite-type LaVO4 were performed in a diamond-anvil cell up to 12GPa. In NdVO4, we found evidence for a non-reversible pressure-induced structural phase transition from zircon to a monazite-type structure at 6.5GPa. Monazite-type LaVO4 also exhibits a phase transition but at 8.6GPa. In this case the transition is reversible and isomorphic. In both compounds the pressure induced transitions involve a large volume collapse. Finally, the equations of state and axial compressibilities for the low-pressure phases are also determined.

New Polymorph of InVO4: A High-Pressure Structure with Six-Coordinated Vanadium

A new wolframite-type polymorph of InVO4 is identified under compression near 7 GPa by in situ high-pressure (HP) X-ray diffraction (XRD) and Raman spectroscopic investigations on the stable orthorhombic InVO4. The structural transition is accompanied by a large volume collapse (ΔV/V = -14%) and a drastic increase in bulk modulus (from 69 to 168 GPa). Both techniques also show the existence of a third phase coexisting with the low- and high-pressure phases in a limited pressure range close to the transition pressure. XRD studies revealed a highly anisotropic compression in orthorhombic InVO4. In addition, the compressibility becomes nonlinear in the HP polymorph. The volume collapse in the lattice is related to an increase of the polyhedral coordination around the vanadium atoms. The transformation is not fully reversible. The drastic change in the polyhedral arrangement observed at the transition is indicative of a reconstructive phase transformation. The HP phase here found is the only modification of InVO4 reported to date with 6-fold coordinated vanadium atoms. Finally, Raman frequencies and pressure coefficients in the low- and high-pressure phases of InVO4 are reported.

Structural properties of PbVO3 perovskites under hydrostatic pressure conditions up to 10.6 GPa

High-pressure synchrotron x-ray powder diffraction experiments were performed on PbVO3 tetragonal perovskite in a diamond anvil cell under hydrostatic pressures of up to 10.6 GPa at room temperature. The compression behavior of the PbVO3 tetragonal phase is highly anisotropic, with the c-axis being the soft direction. A reversible tetragonal to cubic perovskite structural phase transition was observed between 2.7 and 6.4 GPa in compression and below 2.2 GPa in decompression. This transition was accompanied by a large volume collapse of 10.6% at 2.7 GPa, which was mainly due to electronic structural changes of the V4+ ion. The polar pyramidal coordination of the V4+ ion in the tetragonal phase changed to an isotropic octahedral coordination in the cubic phase. Fitting the observed P–V data using the Birch–Murnaghan equation of state with a fixed of 4 yielded a bulk modulus K0 = 61(2) GPa and a volume V0 = 67.4(1) Å3 for the tetragonal phase, and the values of K0 = 155(3) GPa and V0 = 58.67(4) Å3 for the cubic phase. The first-principles calculated results were in good agreement with our experiments.

Dynamic compression of cerium in the low-pressure γ − α region of the phase diagram

Plate impact experiments were performed to examine the dynamic response of cerium for loading paths that span the well known γ−α phase transition. The anomalous nature of the γ-phase and the large volume collapse at the γ−α boundary resulted in a ramp-wave followed by a shock jump for shock loading. This structured wave provided a convenient means for locating the phase boundary and determining the volume collapse at the transition. Experiments using a preheat capability were performed to obtain equation-of-state data, to locate and determine the volume compression along the phase boundary, and to determine the location of the critical point. Experimental results show that the ramp-wave peak increased with the initial sample temperature consistent with an increase in the transition stress while the magnitude of the shock jump decreased. The data were analyzed to determine the volume compression along the boundary pointing to a critical point at 1.648 ± 0.075 GPa. Additional experiments using a shock-release configuration were used to obtain data during release. All data were in good agreement with calculations from a multiphase equation-of-state that treats the γ and α phases as a binary alloy.

Large Volume Collapse during Pressure-Induced Phase Transition in Lithium Amide

The structural studies of lithium amide (LiNH2) have been performed by synchrotron X-ray diffraction measurements and ab initio density functional theoretical calculations up to 28.0 GPa. It is revealed that LiNH2 undergoes a reversible pressure-induced phase transitions from tetragonal phase (I-4) into the monoclinic phase (P21), which starts from about 10.3 GPa and completes at about 15.0 GPa. This transition is accompanied by about 11% large volume collapse, and this volume collapse is much larger than other complex ternary hydrides. The experimental pressure–volume data for the two phases of LiNH2 are fitted by third-order Birch–Murnaghan equation of state, yielding B0 of 37.2 (1.7) GPa for the tetragonal phase and 7.6 (4.9) GPa for the monoclinic phase with the pressure derivatives at 3.5. We also have calculated the total and partial density of states of the two phases in order to explore the mechanism of the volume reduction.

Shock melting of cerium

Shock-wave experiments were performed to examine the melt transition for cerium. Despite past work which points to a higher-pressure transition, the large volume collapse associated with the low-pressure $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\alpha}$ phase transition is expected to result in a low-pressure melt transition. Multiple experimental configurations including front-surface impact and transmission experiments using velocimetry were used to obtain Hugoniot data and sound-speed data for impact stresses up to approximately 18 GPa. Sound-speed data exhibit a structured release consisting of a longitudinal wave followed by a slower plastic wave. The difference between these two wave speeds is observed to decrease with increasing impact stress until a single shock wave is observed indicating the onset of the melt transition which was estimated to be $10.24\ifmmode\pm\else\textpm\fi{}0.34\text{ }\text{GPa}$. Additional data show that the sound speed is in agreement with liquid data at approximately 18 GPa likely indicating the completion of the melt transition. Further results and implications are discussed.

Topologically Ordered Amorphous Silica Obtained from the Collapsed Siliceous Zeolite, Silicalite-1-F: A Step toward “Perfect” Glasses

A dense amorphous form of silica was prepared at high pressure from the highly compressible, siliceous zeolite, silicalite-1-F. Reverse Monte Carlo modeling of total X-ray scattering data shows that the structure of this novel amorphous form of SiO(2) recovered under ambient conditions is distinct from vitreous SiO(2) and retains the basic framework topology (i.e., chemical bonds) of the starting crystalline zeolite. This material is, however, amorphous over the different length scales probed by Raman and X-ray scattering due to strong geometrical distortions. This is thus an example of new topologically ordered, amorphous material with a different intermediate-range structure, a lower entropy with respect to a standard glass, and distinct physical and mechanical properties, eventually approaching those of an "ordered" or "perfect" glass. The same process in more complex aluminosilicate zeolites will, in addition, lead to an amorphous material which conserves the framework topology and chemical order of the crystal. The large volume collapse in this material may also be of considerable interest for new applications in shock wave absorption.

Ab‐initio investigation of structural, electronic and optical properties for three phases of ZnO compound

AbstractThe complex density‐functional theory (DFT) calculations of structural, electronic and optical properties for the three phases: wurtzite (B4), zincblende (B3) and rocksalt (B1) of ZnO compound have been reported using the full‐potential linearized‐augmented plane‐wave (FP‐LAPW) method as implemented in the WIEN2k code. We employed both the local‐density approximation (LDA) and the generalized‐gradient approximation (GGA), which is based on exchange–correlation energy optimization to calculate the total energy. Also, we have used the Engel–Vosko GGA formalism, which optimizes the corresponding potential for band‐structure calculations. The 3d orbitals of the Zn atom were treated as the valence band. The calculated structural properties (equilibrium lattice constant, bulk modulus, etc.) of the wurtzite and rocksalt phases are in good agreement with experiment. The B4 structure of ZnO is found to transform to the B1 structure with a large volume collapse of about 17%. The phase transition pressure obtained by using LDA is about 9.93 in good agreement with the experimental data. B1‐ZnO is shown to be an indirect bandgap semiconductor with a bandgap of 1.47 eV, which is significantly smaller than the experimental value (2.45 ± 0.15 eV). While B3 and B1 phases have direct bandgap semiconductors with bandgaps 1.46 and 1.57 eV, respectively. Also, we have presented the results of the effective masses. We present calculations of the frequency‐dependent complex dielectric function ε (ω) and it zero‐frequency limit ε1(0). The optical properties of B4 phase show considerable anisotropic between the two components. The reflectivity spectra has been calculated and compared with the available experimental data. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pressure-induced antifluorite-to-anticotunnite phase transition in lithium oxide

Using synchrotron angle-dispersive x-ray diffraction and Raman spectroscopy on samples of ${\mathrm{Li}}_{2}\mathrm{O}$ pressurized in a diamond anvil cell, we observed a reversible phase change from the cubic antifluorite ($\ensuremath{\alpha}$, Fm-3m) to orthorhombic anticotunnite ($\ensuremath{\beta}$, Pnma) phase at $50(\ifmmode\pm\else\textpm\fi{}5)\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at ambient temperature. This transition is accompanied by a relatively large volume collapse of $5.4\phantom{\rule{0.3em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.8)%$ and large hysteresis upon pressure reversal (${P}_{\mathit{\text{down}}}$ at $\ensuremath{\sim}25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$). Contrary to a recent study, our data suggest that the high-pressure $\ensuremath{\beta}$-phase $({B}_{o}=188\ifmmode\pm\else\textpm\fi{}12\phantom{\rule{0.3em}{0ex}}\mathrm{GPa})$ is substantially stiffer than the low-pressure $\ensuremath{\alpha}$-phase $({B}_{o}=90\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.3em}{0ex}}\mathrm{GPa})$. A relatively strong and pressure-dependent preferred orientation in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}\mathrm{O}$ is observed. The present result is in accordance with the systematic behavior of antifluorite-to-anticotunnite phase transitions occurring in the alkali-metal sulfides.

Structure of nanocrystalline ZnO up to 85GPa

Abstract The structure of nanocrystalline and bulk polycrystalline ZnO were examined up to 85 GPa and 50 GPa, respectively using synchrotron X-rays and diamond anvil cells at ambient conditions. The transition from the wurtzite to the rock salt phase in the nano-ZnO takes place at 10.5 GPa; this transition pressure is 1.5 GPa higher than in bulk ZnO. A large volume collapse of about 17.5% is observed during the transition in both systems. The rocksalt phase is stable and no structural transitions are observed for both compounds at higher pressures up to the experimental limit. On decompression the rocksalt phase is found to co-exist with the wurtzite phase at ambient conditions for the nano-ZnO.

Pressure-induced valence change in the rare earth metals: The case of praseodymium

The rare earth metal praseodymium (Pr) transforms from the d-fcc crystal structure (Pr-III) to α -U one (Pr-IV) at 20 GPa with a large volume collapse ( Δ V / V = 0.16 ), which is associated with the valence change of the Pr ion. The two 4f electrons in the Pr ion is supposed to be itinerant in the Pr-IV phase. In order to investigate the electronic state of the phase IV, we performed the high-pressure electrical resistance measurement using the diamond anvil cell up to 32 GPa. In the Pr-IV phase, the temperature dependence of the resistance shows an upward negative curvature, which is similar to the itinerant 5f electron system in actinide metals and compounds. This suggests the narrow quasiparticle band of the 4f electrons near the Fermi energy. A new phase boundary is found at T 0 in the Pr-IV phase. From the temperature and magnetic field dependences of the resistance at 26 GPa, the ground state of the Pr-IV phase is suggested to be magnetic. Several possibilities for the origin of T 0 are discussed.

Electrical resistivity measurement on the rare earth metal praseodymium under high pressure up to 32 GPa

The rare earth metal praseodymium (Pr) transforms from the d-FCC crystal structure (Pr-III) to the α -U type one (Pr-IV) at 20 GPa with a large volume collapse ( Δ V / V = 0.16 ). It has been considered that the 4f electrons in Pr ion change from the localized to itinerant states across the transition. In order to investigate the electronic state of the phase IV, we performed the high pressure electrical resistivity measurement using the diamond anvil cell (DAC) up to 32 GPa. In the Pr-IV phase, the resistivity shows an upward curvature, which suggests the narrow energy band of the itinerant 4f electrons near Fermi energy. At higher temperature side of the Pr-IV phase, the resistivity shows a small hump-like anomaly at T 0 .