Search

We report the results of a study of the polycrystalline powder of the diamond-lonsdaleite from the Popigai crater (Siberia) using UV micro-Raman spectroscopy and high-resolution synchrotron X-ray diffraction. By subtracting two experimental Raman spectra of diamond-lonsdaleite samples with close amounts of diamond and lonsdaleite, we were able to identify the polytypic composition of impact diamonds in contrast to the method of X-ray diffraction. We have managed to get for the first time the spectrum of “pure” lonsdaleite. Its deconvolution has allowed us to identify all the three Raman - active vibrational modes E2g, A1g, and E1g whose positions agree well with the results of ab initio calculations.

Nitrate crystals reveal nonlinear optical properties and could be considered as converters of laser radiation in the short-wave region. The conditions for obtaining and basic properties of K2Ba(NO3)4 double nitrate crystals were investigated. Crystal growth was implemented by slow cooling in the temperature range of 72–49 °C and low rate evaporation. The structural analysis of K2Ba(NO3)4 formation on the basis of two mixed simple nitrate structures is discussed. The main groups of oscillations in K2Ba(NO3)4 crystal were revealed using Raman and IR spectroscopy, and the table of vibrations for this compound was compiled. The electronic structure of K2Ba(NO3)4 was elucidated in the present work from both experimental and theoretical viewpoints. In particular, X-ray photoelectron spectroscopy (XPS) was employed in the present work to measure binding energies of the atoms constituting the titled compound and its XPS valence-band spectrum for both pristine and Ar+ ion-bombarded surfaces. Further, total and partial densities of states of constituent atoms of K2Ba(NO3)4 have been calculated. The calculations reveal that the O 2p states dominate in the total valence-band region of K2Ba(NO3)4 except of its bottom, where K 3p and Ba 5p states are the principal contributors, while the bottom of the conduction band is composed mainly of the unoccupied O 2p states, with somewhat smaller contributions of the N 2p∗ states as well. With respect to the occupation of the valence band by the O 2p states, the present band-structure calculations are confirmed by comparison on a common energy scale of the XPS valence-band spectrum and the X-ray emission O Kα band for the K2Ba(NO3)4 crystal under study. Furthermore, the present calculations indicate that the K2Ba(NO3)4 compound is a direct-gap material.

Knowledge about the stability of hydrous borates and borosilicates at high pressures are of critical importance to our understanding on the boron geochemical cycle. Raman spectroscopic measurements of parasibirskite CaHBO3, containing the [BO2(OH)] groups, have been made to pressures up to 5.4GPa. The Raman data show that a progressive structural evolution from ambient pressure to 5.4GPa can be accounted for by the same monoclinic phase P21/m, where the splitting of several Raman bands observed at some pressures is interpreted as the effect of the complex disordering in the H-bond network that has bifurcated H-bonds and ½-occupied H sites. There is no unambiguous evidence for phase transition to the ordered P21 monoclinic phase predicted by first-principles calculations at T=0K (W. Sun et al., Can. Miner., 2011). On the contrary, the disordering of parasibirskite, evidenced by the widening and attenuating Raman spectra, increases markedly at high pressures above 4.5GPa that results in incipient amorphization. Comparison of theoretical (lattice-dynamical) and experimental Raman spectra allows the reliable interpretation of almost all observed bands. The strongest symmetric B-O stretching band v1 at the wavenumber 908cm-1, which is split into a doublet at high pressures, exhibits a shift rate of 4.22cm-1/GPa for the main component.

Carbonaceous materials in black-shale rock specimens from three gold-ore deposits located in Russia and Kazakhstan have been investigated by micro-Raman spectroscopy using near-ultraviolet, visible, and near-infrared wavelength excitation. Only the 325-nm (3.8 eV) wavelength laser line excitation yielded the Raman spectra for all samples. The first-order Raman spectra of these carbonaceous materials have facilitated the classification of all the samples obtained from the different deposits into two groups: the observed wavenumber of the G-band around 1581 cm−1 with a band halfwidth from 23 to 40 cm−1 was observed in samples of the first type, and the observed wavenumber of the G-band near 1600 cm−1 with a band halfwidth from 46 to 73 cm−1 was characteristic in samples of the second type. From these Raman spectra, it has been possible to estimate the graphitization temperature, which was found to range between 380 and 450°С for samples of the first type and from 250 to 400°С for samples of the second type. It has also been shown that the carbonaceous materials are substantially varied in their structural order both in samples obtained from the same deposit and, to a greater extent, in samples obtained from the black-shale ore deposits of different types. Copyright © 2015 John Wiley & Sons, Ltd.

A study of Carica Papaya L. organs was carried out and was noted that the roots of Carica papaya cultivated in Ryazan under controlled green house conditions contains water-soluble polysaccharides, saponins, fructozanes and essential oils. It has also been established that the essential oil derived consists mainly of phenyl-isothiocyanate and other isothiocynates.

The pressure-induced anomalously high AC conductivity of zeolite NaA mixed with water was measured by impedance spectroscopy at various water/zeolite ratios. The conductivity reaches a maximum value at 0.9–1.4 GPa with increasing water content of up to 20 wt.% in NaA + water. The high ionic conductivity of NaA compressed in water is interpreted to result from cation diffusion in the quasi-liquid Na+–H2O intra-channel system enhanced by the filling of additional H2O sites. The pressure range of anomalously high AC conductivity in NaA enlarges towards higher pressures with decrease of the water/zeolite ratio. An abrupt drop in conductivity observed at P > 1.5 GPa appears to be associated with freezing of intra-channel water. After pressure release, the overhydrated state of the zeolite kept in a closed container can be preserved for a long time, providing abnormally high conductivity which is comparable with that of Na+ β-alumina.

A model of phase transitions in double-well Morse potential is developed. Application of this model to the hydrogen bond is based on ab initio electron density calculations, which proved that the predominant contribution to the hydrogen bond energy originates from the interaction of proton with the electron shells of hydrogen-bonded atoms. This model uses a double-well Morse potential for proton. Analytical expressions for the hydrogen bond energy and the frequency of O–H stretching vibrations were obtained. Experimental data on the dependence of O–H vibration frequency on the bond length were successfully fitted with model-predicted dependences in classical and quantum mechanics approaches. Unlike empirical exponential function often used previously for dependence of O–H vibration frequency on the hydrogen bond length (Libowitzky, Mon. Chem., 1999, vol.130, 1047), the dependence reported here is theoretically substantiated.

Layer silicates F- and OH-apophyllites, KCa4Si8O20(F, OH)·8H2O, have been investigated by Raman spectroscopy at hydrostatic and nonhydrostatic pressures up to ~8 GPa in diamond anvil cells using a 4 : 1 methanol–ethanol mix as pressure-transmitting medium. Our experiments show that at hydrostatic compression, apophyllites retain their crystalline states (i.e. no amorphization) up to 5 GPa. The wavenumbers of most bands exhibit linear dependences on pressure, except for a few ones, e.g. at 162 and 3565 cm–1 in OH-form (160.5 and 3558 cm–1 in F-form) that show nonlinear dependences. Nonhydrostatic compression with additional uniaxial loading induces amorphization of apophyllites. The majority of the bands in OH-apophyllite decreases markedly in intensity and shows considerable broadening under nonhydrostatic compression up to 3–6 GPa. In addition, the wavenumbers of several bands at nonhydrostatic compression exhibit considerable nonlinear dependences on pressure with strong hysteresis. These bands are mainly associated with vibrations of the interlayer ions and molecules and also of stretching and bending silicate sheets, hence being highly sensitive to the interlayer distance. Finally, we have calculated the lattice dynamics of F-apophyllite and interpreted the majority of bands, and these data are used to explain the complex baric behavior of the bands. Copyright © 2011 John Wiley & Sons, Ltd.

The series of phase transitions on increasing pressure and on reverse decompression was followed in crystals of monoclinic and orthorhombic polymorphs of L-cysteine by using Raman spectroscopy, with the samples placed in a diamond anvil cell together to ensure identical pressures on the two samples. The effects of hydrostatic pressure on the two polymorphs are shown to be radically different. Depending on the starting polymorph, different phases are formed under identical compression/decompression conditions. The effect of pressure on the monoclinic polymorph was studied for the first time. Phase transitions in monoclinic L-cysteine (at ∼2.9 and ∼3.9 GPa) are completely reversible without a noticeable hysteresis. The changes in the spectra suggest that the H-bond network is distorted and SH···O bonding dominates over SH···S bonding at high pressures, but the molecular conformations change continuously during these transitions. The data on the orthorhombic polymorph of L-cysteine show that not only the H-bond network is distorted, but also the conformation of the L-cysteine zwitterion changes very substantially. The previously observed discrepancy in the results related to the occurrence of a phase existing between 2.1 and 2.3 GPa reported by Minkov et al. (J. Phys. Chem. B. 2008; 112, 8851) but not observed by Moggach et al. (Acta Crystallogr. B. 2006; 62, 296) could be interpreted; different phases can be formed at the same pressure, depending on how this pressure was reached: on direct compression, or in the compression–decompression–compression cycle. Copyright © 2010 John Wiley & Sons, Ltd.

Experimental investigation of the phase diagram of the system carbon dioxide-water at pressures up to 2.7 GPa has been carried out in order to explain earlier controversial results on the decomposition curves of the hydrates formed in this system. According to X-ray diffraction data, solid and/or liquid phases of water and CO2 coexist in the system at room temperature within the pressure range from 0.8 to 2.6 GPa; no clathrate hydrates are observed. The results of neutron diffraction experiments involving the samples with different CO2/H2O molar ratios, and the data on the phase diagram of the system carbon dioxide-water show that CO2 hydrate of cubic structure I is the only clathrate phase present in this system under studied P-T conditions. We suppose that in the cubic structure I hydrate of CO2 multiple occupation of the large hydrate cavities with CO2 molecules takes place. At pressure of about 0.8 GPa this hydrate decomposes into components indicating the presence of the upper pressure boundary of the existence of clathrate hydrates in the system.

Hydrated and dehydrated zeolites MA (where M=Li, Na and K) with LTA structure have been studied by impedance spectroscopy with scanning frequency from 1 Hz to 1 MHz at high pressure up to 4.5 GPa and high temperature up to 250 °C. Anomalous increase in electrical AC conductivity at about 1.5–2 GPa observed in hydrated zeolites is associated with changes in crystalline structure leading to the formation of high-diffusion state of cation and water stuffing of the channels. In dehydrated zeolites, electrical conductivity is controlled by diffusion of cations (Li + , Na + and K + ), which is determined by cation sites and aluminosilicate ring windows. LiA and NaA zeolites show normal decrease of conductivity with pressure, whereas KA zeolite exhibits the anomalous dependence with considerable increase and then fast decrease of conductivity. The behaviour of KA zeolite is associated with nearly central location of cation site in 8-membered ring, different from that in LiA and NaA zeolites.

Dissociation temperatures of gas hydrate formed in the ethane-water system were studied at pressures up to 1500 MPa. In situ neutron diffraction analysis and X-ray diffraction analysis in a diamond anvil cell showed that the gas hydrate formed in the ethane-water system at 340, 700, and 1840 MPa and room temperature belongs to the cubic structure I (CS-I). Raman spectra of C-C vibrations of ethane molecules in the hydrate phase, as well as the spectra of solid and liquid ethane under high-pressure conditions were studied at pressures up to 6900 MPa. Within 170-3600 MPa Raman shift of the C-C vibration mode of ethane in the hydrate phase did not show any discontinuities, which could be evidence of possible phase transformations. The upper pressure boundary of high-pressure hydrate existence was discovered at the pressure of 3600 MPa. This boundary corresponds to decomposition of the hydrate to solid ethane and ice VII. The type of phase diagram of ethane-water system was proposed in the pressure range of hydrate formation (0-3600 MPa).

Energies and lattice dynamics of cubic and hexagonal phases of RbMnCl3 crystal have been calculated non-empirically within a modified Gordon–Kim model. At normal pressure the crystal has been demonstrated to have a six-layer hexagonal structure. Above 1.1 GPa RbMnCl3 is found to transform into the cubic phase. Calculated lattice vibrational frequencies are compared with available experimental data.

A Raman spectroscopy study has proven, that on increasing hydrostatic pressure up to ∼3 GPa γ-glycine undergoes a phase transition into δ-polymorph, which on decompression down to 0.62 GPa transforms into another form, supposed to be a previously unknown polymorph termed ζ-glycine. The formation of this new form was observed also visually using optical microscopy and is in an agreement with the data from X-ray powder diffraction. On further decompression, δ- and ζ-forms coexisted in the pressure range between 0 and 0.62 GPa. The ζ-form of glycine was preserved at ambient conditions for at least 3 days.

Amorphization of natrolite Na 2 [Al 2 Si 3 O 10 ]2H 2 O (Khibiny, Kola Peninsula, Russia) and edingtonite Ba[Al 2 Si 3 O 10 ]4H 2 O (Bohlet, Sweden) was investigated at high pressures up to 11 GPa, using Raman spectroscopy. Natrolite compressed in a non-penetrating medium of methanol-ethanol shows one apparent crystal-to-crystal transition at approximately 3.7 GPa before amorphization. Amorphization, reflected by decrease of Raman spectrum intensity, starts in the pressure range of 6–7 GPa and is completed by ~9 GPa. Amorphized Na 2 [Al 2 Si 3 O 10 ]2H 2 O exhibits partial reversibility to crystalline natrolite after amorphization at ~7-8 GPa and partially recovers its Raman spectrum after release of pressure. It was shown that amorphization of natrolite begins in soft structural units (water sublattice) and finishes in rigid units (T-O bonds). Comparison of natrolite and edingtonite behaviour at high pressures shows that amorphization of both zeolites begins at similar pressures but differ in their crystalline phase transitions. Edingtonite compressed in methanol-ethanol has no crystalline transition at high pressure. Ba[Al 2 Si 3 O 10 ]4H 2 O amorphized after compression up to higher pressure of ~11 GPa also exhibits partial reversibility to edingtonite crystal structure on release of pressure.

Several examples of the comparative variable-temperature and variable-pressure studies of the small-molecule organic crystals are discussed. Selected systems represent the crystals with non- spherical flexible molecules / molecular fragments and with different types of intermolecular interactions, ranging from van der Waals interactions to hydrogen bonds of various types (OH…O, NH…OH, NH…O=C). A special attention is payed to the studies of solid drugs (polymorphs of paracetamol), amino acids (polymorphs of glycine, L-serine, D,L-serine), and dipeptides (glycilglycine and glycilglycine hydrate) by structural, spectroscopic and calorimetric techniques. The anisotropy of structural distortion within the range of stability of the same phase, as well as the phase transitions induced by changes in temperature or pressure are discussed.

Single crystals of β-glycine were studied at pressures up to 7.6 GPa in a diamond anvil cell (DAC) in situ by Raman spectroscopy and polarized optical microscopy. A reversible phase transition was observed at 0.76 GPa. A boundary between the two phases could be observed in the microscope if the phase transition was slow enough. The phase transition was accompanied by cracking of the crystal. The birefringence in the high-pressure phase 2 was close to that in the starting phase 1, so that the phase transition can be supposed to preserve the monoclinic crystal system. Every vibrational band in the spectrum of the high-pressure phase can be related to a corresponding band in the starting phase, excluding lattice vibrations. The frequencies of most vibrations changed by a jump at the transition point. Low-frequency lattice modes showed linear pressure dependence when pressure increased from 0.76 to 7.6 GPa. This can be a manifestation of the softening of the libration modes of glycine at the phase transition point. At high pressures (in the range of 6.5–7.6 GPa) the shifts of the frequencies of some vibrational bands were nonlinear. This can be related to the rotations and twisting of the zwitter-ions of glycine.

Edingtonite is a ferroelectric material of the Rochelle salt (RS) class and shows large anomalies of different properties in the temperature range of −53 to −133 °C. Classical RS exhibits the low-temperature phase transition P21212–P2111, whereas ammonium RS shows the phase transition P21212–P11211. According to our data, edingtonite blocks this possible symmetry lowering by the phase transition P21212–P112. Edingtonite, similarly to RS crystals, has two sub-lattices of water molecules and exhibits a complex low-temperature behavior. There are at least three anomalies in the low-temperature dependence of the generation of the second optical 0.53-micron harmonics, excited by the 1.06-micron line of a Nd pulse laser. Edingtonite also exhibits significant anomalies in the low-frequency range of its IR spectrum at low temperatures. The maximum IR anomaly is observed in natural edingtonite at −124 °C, whereas in the deuterated sample the same anomaly occurs at −113 °C. The most intense anomalous broad band at 220 cm−1 did not shift due to deuteration. According to the presented lattice-dynamical calculations, this vibration corresponds to a strong deformation of the cavity around the water molecules during the phase transition. Raman study of edingtonite under high pressure in a diamond anvil cell (DAC) at room temperature shows that there is no pressure-induced phase transition up to 6.4 GPa. No amorphization was observed at this pressure range.

Polarized single-crystal Raman scattering and powder infrared absorption spectra of Fdd2 orthorhombic natural natrolite (Na1.88 K0.02 Ca0.04 )(Al1.96 Si3.03 O10)⋅2.03 H2O from Khibiny, Kola peninsula, were measured. Using short-range models, lattice-dynamical calculations were performed for an idealized natrolite structure Na4(Al4Si6O20)4H2O containing 46 atoms in the primitive unit cell (Z = 2). By varying the valence force constants, the calculated frequencies in the Raman and IR spectra were fitted to the observed frequencies. On considering their calculated intensities as well, nearly all the observed bands (especially those corresponding to the A1 modes) could be unambiguously assigned and interpreted. The external vibrations of H2O could be correctly assigned using deuter- ated samples. The strongest Raman band at 534 cm-1 corresponds to a breathing mode of the four-membered alumi- nosilicate ring. The calculated bulk modulus (52.7 GPa at zero pressure) is close to the experimental value of 47 ± 6 GPa. The natrolite structure has some advantages upon other zeolites to understand the amorphization mechanism, because samples of this mineral surrounded by a non-penetrating medium show no crystal phase transitions with increasing pressure. Lattice energy minimization calculated with variable unit-cell dimensions shows the crystal structure to become unstable at about 5.5 GPa, thereby apparently explaining the amorphization process at 4-7 GPa. This instability is connected with shear acoustic modes coupled with soft internal framework vibrations.

Dehydrated, hydrated and superhydrated NaA zeolites have been studied by impedance spectroscopy with scanning frequency from 1 Hz to 1 MHz at high pressure up to 4.5 GPa. A considerable anomalous increase in electrical conductivity in the range of 0.5–1.1 GPa was observed in superhydrated NaA zeolite containing additional water in the channels. A very high mobility of ions in superhydrated zeolite may be associated with the liquid-like state of the water-cation stuffing of zeolite channels. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-pressure synchrotron X-ray powder diffraction measurements of a synthetic zeolite NaA were carried out up to 2.5 GPa using pure water as pressure-transmitting (P) medium to provide non-hydrostatic (wet) conditions in a diamond anvil cell. The compressibility of wet zeolite NaA is similar to that measured at hydrostatic compression in water within the P-range 0-0.8 GPa, whereas between 1-2 GPa the zeolite becomes slightly more compressible and progressively amorphizes due to the non-hydrostatic conditions. Rietveld refinement at 0.37 GPa reveals a selective additional filling of the H 2 O sites in α- and β-cage, leading to about 30% increase of the total water content. The over-hydrated state of the zeolite is partially preserved after the pressure release. The over-hydration of zeolite pores, combined with a partial disordering at the onset of amorphization, apparently provides necessary conditions for the P-induced enhancement of water-cationic diffusion and the corresponding increase of ionic conductivity observed in zeolite NaA in non-hydrostatic water medium.

A series of extended reversible phase transitions at approximately 0.1, 1.5, 2.0, and approximately 5 GPa was observed for the first time in the crystals of dl-cysteine by Raman spectroscopy. These are the first examples of the phase transitions induced by increasing pressure in the racemic crystal of an amino acid. In the crystals of the orthorhombic l-cysteine, a sequence of reversible structural changes in the pressure range between 1.1 and 3 GPa could be observed by Raman spectroscopy, instead of a single sharp phase transition at 1.9 GPa reported previously in ( Moggach, et al. Acta Crystallogr. 2006, B62, 296- 309 ). The role of the movements of the side -CH 2SH groups and of the changes in the hydrogen-bonding type in dl- and l-cysteine during the phase transitions with increasing pressure is discussed and compared with that on cooling down to 3 K.

Publisher Summary This chapter presents lattice-dynamical calculations for the zeolites of natrolite group. Strongest Raman bands of natrolite at 534 cm -1 and edingtonite at 530 cm -1 are related for breathing modes of four-membered rings. Assignment of vibrational spectra of used zeolites is presented for symmetric modes of natrolite and may provide a base for interpretation of vibrations in other zeolites. Calculated natrolite crystal structure exhibits instability at about 5.5 GPa, which corresponds to amorphization observed at a pressure range of 4–7 GPa.

The contribution summarizes the results of recent studies of phase transitions induced by high pressure in a number of molecular organic crystals, such as polymorphs of paracetamol, chlorpropamide, polymorphs of glycine, L- and DL-serine, β-alanine. The main attention is paid to the following topics: (1) Reversible / irreversible transformations; (2) Different behavior of single crystals / powders; (3) The role of pressure-transmitting liquid; (4) The role of the kinetic factors: phase transitions on decompression, or after a long storage at a selected pressure; (5) Isosymmetric phase transitions; (6) The role of the changes in the hydrogen bond networks / intramolecular conformational changes in the phase transitions; (7) Superstructures / nanostructures formed as a result of pressure-induced phase transitions.

In the last 20 years, multilayer optics for x-ray and EUV applications have revolutionized the measurement capabilities and the experimental set ups of synchrotron beamlines. Rigaku Innovative Technologies (formerly Osmic) has pioneered these technologies by designing, engineering and manufacturing of distinctive multilayer coatings. We are experienced and internationally recognized for our innovative technologies.We control our production of specified internal roughness on the atomic level while creating layered materials of defined thickness. These multilayers have d-spacings, synonymous for layer-pair thickness, which we can produce uniform, laterally graded, depth graded or even a combination of both gradients. We guarantee our specifications and we have a wide range of metrology technology in house, enabling us to keep our promised specifications and to expand the technical boundaries in our field of applications. Our core capabilities are the detailed knowledge of distinctive multilayer coating technology including the mounting and alignment of optics. We do direct coating on prefigured substrates or, mostly for applications in analytical laboratories, bonding of thin substrates to flat or curved backings. Having delivered thousands of multilayer structures to the analytical scientific market, we are able to design and engineer multilayers on the basis of numerical and analytical simulations of thickness, roughness, required densities and other optical parameters. This technology gives us the possibility to produce just as one example multilayers with a period of 15 Angstroms, a reflectivity of much better than 30% and an energy resolution of better than 0.4%. We also have coatings and multilayer structures for substrates up to 1400 mm length and 400 mm width. The number of chemically different coatings we are able to perform is very broad. This is starting with the classical W/Si through Mo/B4C to a lot of other material combinations. We also design and produce dual wavelength multilayers, narrowand broad-bandwidth multilayers for energy ranges from 40ev to 40 keV. Please see figure (1) for further details. Here we have shown our calculated values for two different multilayer sandwiches. Further material will be shown. Our actual production quality will also be presented.