Structural and crystallization behavior of (Ba,Sr)TiO3 borosilicate glasses

Various glass samples were prepared by melt quench technique in the glass system [(Ba_{1? x} Sr _x ) TiO₃]–[2SiO₂–B₂O₃]–[K₂O] doped with 1?mole% of La₂O₃. Infrared spectra show the number of absorption peaks with different spliting in the wave number range from 450 to 4000?cm^?1. Absorption peaks occurs due to asymetric vibrational streching of borate by relaxation of the bond B–O of trigonal BO₃. Raman spectra show the Raman bands due to ring-type metaborate anions, symmetric breathing vibrations BO₃ triangles replaced by BO₄ tetrahedra, and symmetric breathing vibrations of six-member rings. The differential thermal analysis of a glass sample corresponding to composition x?=?0.0 shows crystallization temperature at 847°C and glass transition temperature at 688°C. X-ray diffraction (XRD) pattern of glass ceramic samples shows the major crystalline phase of BaTiO₃ whereas pyrochlore phases of barium titanium silicate. Scanning electron micrographs confirm the results of XRD as barium titanate is major crystalline phase along with pyrochlore phase of barium titanium silicate.     

Measurements of Rayleigh–Taylor instability growth of laser-shocked iron–silicon alloy

The Rayleigh–Taylor (RT) instability of liquid iron alloys is important for understanding the core formation mechanism in the Earth. Here we first report the measurement of RT instability growth for a liquid iron–silicon (Fe–Si) alloy, which is one of the major candidate for the material of the Earth’s core, using a high power laser. We optimized the measurement setup and analytical technique to observe the growth of perturbation on an Fe–Si sample surface. The growth of perturbation amplitude on the Fe–Si alloy under high pressure and temperature was successfully observed using in situ X-ray radiography. The growth rate of the RT instability for the Fe–Si alloy on about 1000?GPa was estimated to be 0.3 ns^?1.     

Studies on Im-3-type KSbO3 using high pressure X-ray diffraction and Raman spectroscopy

In situ X-ray diffraction and Raman scattering experiments using a diamond anvil cell revealed that Im-3-type KSbO₃ remains stable up to 40.5?GPa with a bulk modulus K₀?=?101.6 (7)?GPa. Rietveld structure refinements and mode Grüneisen parameters suggested that the stability mechanism of this three-dimensional cubic tunnel structure was attributed to the isotropic compression for all types of Sb–O bonding in the unit of SbO₆ octahedron. Isotropic structure adjustment with external pressure reflected the nature that Im-3-type KSbO₃ model structure has a high ionic tolerance with a change in the chemical pressure in the isomorphous substitutions.     

Permanent densification of silica glass for pressure calibration between 9 and 20 GPa at ambient temperature

Permanent density increase of silica glass was used to calibrate pressure generation delivered by cupped sintered diamond anvils (‘dimple anvils’) [Haberl B, Molaison JJ, Neuefeind JC, et al. Simple modified Bridgman anvil design for high pressure synthesis and neutron scattering. High Press. Res. submitted] within the Paris-Edinburgh press between approximately 9 and 20?GPa. Raman spectral changes of recovered silica glass with increased density were used to determine the maximum pressure reached by following an established calibration curve [Deschamps T, Kassir-Bodon A, Sonneville C, et al. Permanent densification of compressed silica glass: a Raman-density calibration curve. J. Phys. Condens. Matter. 2013;25:025402]. The monotonic Raman shift of the Main Band spectral region (～200–700?cm^?1) of silica glass recovered from 9 to 20?GPa allows for continuous pressure calibration and is applicable to all presses that operate within this pressure range. Radial & axial Raman profiles were conducted to determine the pressure distribution within the sample chamber. This technique has been verified by in situ resistance measurements of the insulator-to-metal phase transition of ZnS near 15?GPa.     

Physical and mechanical properties of C60 under high pressures and high temperatures

The physical and mechanical properties of a C₆₀ fullerene sample have been investigated under high pressure–high temperature conditions using a designer Diamond Anvil Cell. Electrical resistance measurements show evidence of C₆₀ cage collapse at 20 GPa, which leads to the formation of an insulating phase at higher pressure. Energy dispersive X-ray diffraction (EDXD) data indicated that the characteristic fcc reflections gradually decrease in intensity and eventually disappear above 28 GPa. A C₆₀ sample was laser-heated at a pressure of 35 GPa to a temperature of 1910±100 K and, subsequently, decompressed to ambient conditions. The photoluminescence spectra and the Raman spectrum of the pressure–temperature-treated sample were measured at a low temperature of 80 K. Raman peak at 1322.3 cm^?1 with full-width half-maximum of 2.9 cm^?1 was observed from the sample, which is attributed to the hexagonal diamond phase in the sample. The room temperature photoluminescence spectra showed a symmetric emission band centered in the red spectral range with a peak at 690 nm. The structural analysis of the pressure–temperature-processed C₆₀ sample using EDXD method showed strong internal structure orientation and a phase close to hexagonal diamond. Mechanical properties such as hardness and Young’s modulus were measured by nanoindentation technique and the values were found to be 90±7 and 1215±50 GPa, respectively and these values are characteristic of sp³-bonded carbon materials.     

High pressure effect on structural and spectroscopic properties of Sm3+-doped alkali silicate glasses

Structural and spectroscopic properties of Sm³⁺-doped alkali silicate glasses were investigated after densification at 7.7?GPa in a large volume high pressure apparatus. The glass composition was 33M₂O?+?66SiO₂?+?1Sm₂O₃, where M?=?Li, Na or K. Raman and infrared spectroscopy revealed small changes in the vibrational modes dependent on the alkali ion. Irreversible changes were observed in the optical absorption spectra of Sm³⁺ ions. The Judd–Ofelt parameters were calculated to evaluate the effect of pressure on the local field. For lithium silicate, Ω₂ parameter increased, suggesting the densification increased the local asymmetry of the Sm³⁺ environment. For sodium silicate, this parameter decreased considerably, suggesting the opposite effect on the local field, while for potassium silicate, it remained practically unchanged. The changes induced by high pressure are probably due to the irreversible changes in the distances and bond angles between the rare earth ion and the ligands.     

Pressure-induced phase transitions in gypsum

Abstract

We report high-pressure Raman scattering spectroscopy and energy dispersive X-ray diffraction investigations on gypsum, CaSO₄ · 2H₂O, at room temperature in a diamond cell. With increasing pressure, measurements indicate that CaSO₄ · 2H₂O undergoes two stages of crystalline-state phase transitions at 5 and 9 GPa, and then converts to a disordered phase above 11 GPa. The structures of the three high-pressure phases of gypsum have not been determined yet. These phases are tentatively named as “post-gypsum-I” (PG-I), “post-gypsum-II” (PG-II) and “disordered” according to the sequence of their appearance with pressure.

Gypsum shows anisotropic compressibility along three crystallographic axes with b > c > a below 5 GPa. The difference in the behavior of the two OH stretching modes in gypsum is attributed to the different reduction rate in the hydrogen bonding distances by the anisotropic axial compressibility.     

High pressure X-ray diffraction and Raman spectroscopic studies of the phase change of D2O ice VII at approximately 11 GPa

High pressure experiments were performed on D₂O ice VII using a diamond anvil cell in a pressure range of 2.0–60 GPa at room temperature. In situ X-ray diffractometry revealed that the structure changed from cubic to a low symmetry phase at approximately 11 GPa, based on the observed splitting of the cubic structure's diffraction lines. Heating treatments were added for the samples to reduce the effect of non-hydrostatic stress. After heating, splitting diffraction lines became sharp and the splitting was clearly retained. Although symmetry and structure of the transformed phase have not been determined, change in volumes vs. pressure was calculated, assuming that the low-symmetry phase had a tetragonal structure. The bulk modulus calculated for the low-symmetry phase was slightly larger than that for the cubic structure. In Raman spectroscopy, the squared vibrational frequencies of ν₁ (A_1g), as a function of pressure, showed a clear change in the slope at 11–13 GPa. The full width at half maxima of the O-D modes decreased with increasing pressure, reaching a minimum at approximately 11 GPa, and increased again above 11 GPa. These results evidently support the existence of phase change at approximately 11 GPa for D₂O ice VII.     

Brillouin and raman scattering from glasses under high pressure

Abstract

Brillouin and Raman Scattering Spectra in SiO₂ and GeO₂ glasses have been measured in a diamond anvil cell up to pressures of 14 GPa. The elastic properties and equation of state for each glass type were obtained from the Brillouin scattering measurements with respect to pressure. Both elastic constants and compressibility of SiO₂ and GeO₂ showed anomalous behavior with respect to pressure. This anomalous behavior is reconciled with a model based on the pressure dependent bending of the oxygen angles in both glass types. The Raman measurements corroborate the conclusions from the Brillouin scattering results, namely that the SiO₂ and GeO₂ bond angles are changing with pressure or the oxygen angle distribution is changed without bond breaking.     

Pressure-induced disordering and phase transformations in Eu2Zr2O7 pyrochlore

ABSTRACT

The structural properties of pyrochlore Eu₂Zr₂O₇ under high pressure have been studied by using Raman spectroscopy and in situ angle-dispersive X-ray diffraction (ADXRD). The results of Raman spectra indicate that Eu₂Zr₂O₇ undergoes a reversible structural change around 21.2?GPa. The results of Rietveld refinements from in situ ADXRD data indicate that the ordered pyrochlore structure (Fd-3m) transforms to the defect-cotunnite structure (Pnma) at 26.5?GPa. The phase transition is irreversible and the transformation process is mainly induced by the accumulations of anti-site defects of the cation sublattice and Frenkel defects on the anion sublattice. Besides, the <Zr–O> bonds should play a more important role than the <Eu–O> bonds in the process of the phase transformation.     

Phase transformations in calcite from electrical impedance measurements

The phase transformation in calcite I-IV-V and calcite ? aragonite have been characterized by electrical impedance measurements at temperatures 600–1200°C and pressures 0.5–2.5?GPa in a piston cylinder apparatus. The bulk conductivity σ has been measured from Argand plots in the frequency range 10⁵–10^?2?Hz in an electric cell representing a coaxial cylindrical capacitor. The synthetic polycrystalline powder of CaCO₃ and natural crystals of calcite were used as starting materials. The transformation temperature T_c was identified from resistivity-temperature curves as a kink point of the activation energy. At pressure above 2?GPa in ordered phase calcite I, the activation energy E _σ is c. 1.05?eV, and in disordered phase calcite V E _σ is c. 0.75?eV. The pressure dependence of T_c for the rotational order–disorder transformation in calcite is positive for pressures <1?GPa and negative for pressures >1?GPa. The transformation boundary of calcite 1–IV is observed only during first heating in samples after a long annealing at low temperatures. The activation energy of calcite I???IV decreases gradually from 1.8 to 1.05?eV with the pressure increase from 0.5 to 2?GPa. The kinetics of calcite ? aragonite transformation has been monitored by measuring a time-variation of the electrical resistance of a calcite sample at 10³?Hz in the stability P-T field of aragonite. The variation of the impedance correlates with the degree of phase transformation, estimated from X-ray powder diffraction studies on quenched products of experiments. The kinetics of calcite ? aragonite transformation may be fitted to the Avrami kinetics with the exponent m???1–1.5.     

Strength and equation of state of molybdenum triboride under 80 GPa pressure,using radial X-ray diffraction

The strength and equation of state of molybdenum triboride have been determined under nonhydrostatic compression up to 80?GPa, using an angle-dispersive radial X-ray diffraction technique in a diamond anvil cell (DAC). The RXD data yield a bulk modulus and its pressure derivative as K_0?=?342(6)?GPa with K₀′?=?2.11(17) at ψ?=?54.7°. Analysis of diffraction data using the strain theory indicates that the ratio of differential stress to shear modulus (t/G) ranges from 0.002 to 0.050 at pressures of 4–80?GPa. Together with theoretical results on the high pressure shear modulus, our results here show that molybdenum triboride sample under uniaxial compression can support a differential stress of ～10?GPa when it started to yield with plastic deformation at ～30?GPa. In addition, we draw a conclusion that MoB₃ is not a superhard material but a hard material.     

Raman study of thaumasite Ca3Si(OH)6(SO4)(CO3)⋅12H2O at high pressure

Thaumasite, Ca₃Si(OH)₆(SO₄)(CO₃)⋅12H₂O, is an extraordinary mineral that possibly plays a special role in the carbonate–sulfate–silicate balance of the Earth's crust. Thaumasite, an undesirable component in concrete, remains a material poorly studied at high pressures in various media except for He medium (M. Ardit et al., Mineral. Mag., 2014). In the present Raman study, thaumasite samples were compressed in alcohol–water and KBr media at high pressures up to ~7 GPa: several phase transformations were identified. In samples compressed in alcohol–water, the wavenumbers of intense Raman bands of S O and С О symmetric stretching vibrations at 991 and 1074 cm⁻¹ proved to exhibit similar dependences on pressure: during a first transition I → II at 4.4 GPa, the wavenumbers of both bands exhibited a downward jump; at a second transition II → III, which occurred at 4.9 GPa, each band split in a doublet; and then, at a third transition III → IV, which was observed at 5.4 GPa, each doublet band transformed in a singlet. In KBr medium, these and other Raman bands of thaumasite showed similar (to those in thaumasite at compression in alcohol–water) dependences on pressure, revealing several phase transitions with slightly shifted transition points, the first transition I → II, however, being not distinguished. Taking into account the similar behaviors in both media, the transitions are assumed to be polymorphic: no noticeable overhydration in thaumasite compressed in water–alcohol occurred. In phase IV, gradual widening and weakening of each band were observed; those changes can be attributed to amorphization of the material. Considerable hysteresis was observed at thaumasite decompression. Copyright © 2016 John Wiley & Sons, Ltd.     

High-pressure Raman and X-ray studies of barite,BaSO4

High-pressure Raman spectroscopic and X-ray diffraction experiments of barite, BaSO₄, were carried out in a diamond anvil cell up to 25?GPa at room temperature. On the basis of the changes in the diffraction patterns and the variation of lattice parameters with pressure, it is inferred that barite undergoes a phase transformation at 10?GPa. The phase transition accompanies the change in the force constant of vibrational modes in barite. Further compression beyond the phase transition causes the distortion of SO₄ tetrahedron as indicated by the splitting in the SO₄ stretching modes. Both X-ray and Raman data support that the phase transition in BaSO₄ is reversible. The compression data yield a bulk modulus of 63?±?2?GPa for barite. Barite shows anisotropic compressibility along three crystallographic axes with c being the most compressible axis.     

High-energy X-ray diffraction of a hydrous silicate liquid under conditions of high pressure and temperature in a modified hydrothermal diamond anvil cell

In situ high-energy X-ray diffraction measurements were made for the first time on a water-saturated silicate melt at high pressure and temperature. A modified hydrothermal diamond anvil cell (HDAC), designed to minimize the path length of the X-ray beam within a diamond anvil and to increase the solid angle of the diffracted beam, was used to reduce high background contributions and extend X-ray diffraction data collection in Q space. Quantitative differential pair distribution function (PDF) analysis of X-ray diffraction data show that the first measurable (Si–O) peak is 0.095 Å greater in length in the hydrous melt than in the starting glass. Contributions from the H₂O O–O correlations, as well as from the second nearest neighbor O–O correlations within the silicate melt, are evident within the second peak of the differential PDF. The procedure described opens new opportunities to directly investigate volatile-rich melts at high pressure and temperature.     

High pressure and low-temperature polymorphism in cyclopentanol

The polymorphism of cyclopentanol (C₅H₁₀O) has been investigated as a function of temperature at ambient pressure and as a function of hydrostatic pressures to 3.7?GPa at room temperature. Differential scanning calorimetry (DSC) and Raman spectra reveal that two plastic phases and two fully ordered crystalline phases are formed during cooling. High pressure Raman and infrared spectra show that cyclopentanol undergoes two-phase transformations. At around 0.6?GPa, the liquid cyclopentanol transforms to a solid plastic structure. On further compression to 1.9?GPa, one fully ordered crystalline phase is observed. Based on pieces of evidence such as peak splitting and emergence of new peaks, it can be concluded that the ordered crystalline structure has a lower symmetry. In addition, the decrease in the wavenumber of the O–H stretching modes at low temperature and high pressure suggests the ordered crystalline phases are characterized by the formation of hydrogen-bonded molecular chains.     

Raman and infrared investigations at room temperature of the internal modes behaviour in solid nitromethane‐h3 and ‐d3 up to 45 GPa

Raman and infrared spectra of internal phonons in solid nitromethane‐h₃ and ‐d₃ were measured as a function of pressure in the range 0–40 GPa at room temperature. Experiments were performed in diamond anvil cells. The evolution of the splitting of the various modes in condition of nearly hydrostatic compression supports the maintenance of the P2₁2₁2₁ crystal structure until the material chemically transforms into an amorphous phase. The observed pressure‐induced shifts of vibrational wavenumbers are consistent with computations recently reported in the literature. Infrared and Raman spectroscopies deliver complementary information on the internal modes behaviour. The continuous evolution of the infrared band shapes suggests a weak molecular distortion during the compression process. The strong modifications that are observed in the Raman bands of the nitro group are attributed to polarization effects arising from a rearrangement of the molecules inside the unit cell in the pressure range 10–12 GPa, a consequence of a close intermolecular O…H approach. Copyright © 2007 John Wiley & Sons, Ltd.     

High pressure structural investigations on hexagonal YInO3

Hexagonal (space group P6₃cm) form of YInO₃ has been investigated under high pressure using synchrotron-based angle-dispersive X-ray diffraction and Raman scattering methods. Our experimental investigations suggest that it undergoes the phase transition to a new phase in the pressure range 12–15?GPa, while the ambient hexagonal phase is found to coexist with the new phase up to 29?GPa. DFT based calculations within the LDA approach on the hexagonal phase of YInO₃ showed that the unit cell volume matches well with the experimentally obtained volume at ambient pressure. As the pressure increases, theoretically obtained values of unit cell volume of the hexagonal phase were found to be significantly lower than that of experimentally obtained values. This discrepancy has been corrected using LDA?+?U_In(4d) (Hubbard interaction parameter between Indium 4d electrons) method. We have proposed the high pressure phase of YInO₃ to be orthorhombic with space group Pnma.     

微波ECR磁控溅射制备SiNx薄膜的XPS结构研究

利用微波电子回旋共振等离子体增强非平衡磁控溅射法在不同N₂流量下制备无氢SiN_x薄膜.通过X光电子能谱、纳米硬度仪等表征技术,研究了不同N₂流量下制备的SiN_x薄膜的化学键结构、化学键含量、元素配比及各元素沿深度分布.研究结果表明,N₂流量是影响SiN_x薄膜化学键结构、元素配比、元素延深度分布等性质的主要因素.在N_{2关键词： x}')" href="#">SiN_x 磁控溅射 XPS 化学键结构     

Raman spectra of shortite Na2Ca2(CO3)3 compressed up to 8 GPa

A rare mineral shortite, Na₂Ca₂(CO₃)₃, occurs among groundmass minerals in unaltered kimberlites, which suggests its participation in the evolution of kimberlite system. This work presents a high pressure Raman spectroscopic study of natural shortite (Udachnaya east kimberlites) compressed in KBr up to 8?GPa in a diamond anvil cell. At ambient pressure the spectrum contains two strong bands related to symmetric C-O stretching vibrations, four in-plane bending modes, and several low-frequency modes of lattice vibrations. Upon the pressure increase up to 8?GPa, almost all the bands exhibit positive shift with the rate of 1–4?cm^?1/GPa for the lattice modes and 3.6 and 3.9?cm^?1/GPa for the C-O stretching modes. The shifts of Raman modes are rather regular, which implies the absence of reconstructive phase transitions within the studied pressure range, similarly to the behavior of nyerereite, a related carbonate mineral. However, minor anomalies in the ν/P and FWHM/P dependences, observed at about 2?GPa, suggest some rearrangement and disordering of carbonate groups. The obtained data can be used for the estimation of residual pressure in shortite-bearing inclusions in deep-seated minerals.