Sergei V. Goryainov

Pressure-Induced Phase Transitions in Crystalline l- and dl-Cysteine

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.

Raman Spectroscopy of Water Tracer Diffusion in Zeolite Single Crystals

The water tracer diffusion in single crystals of natrolite, scolecite, mesolite, heulandite, and chabazite has been studied by Raman micro-spectroscopy. A model of water tracer diffusion is proposed. The H2O, HDO, and D2O molecule concentrations are calculated for a crystal of orthorhombic symmetry on deuteration of the initial H2O-sample. A way is shown to find the diffusion coefficients, the constant of equilibrium, and the deuteron-proton exchange rate from experimental data. The water diffusion coefficients for natrolite placed in liquid D2O appeared to be 1.5–2 times higher than those for a sample in vaporous D2O. For natrolite at room temperature, 1.5–1.6 times higher water diffusion occurs along [001] than along [110].

Phase Diagram and High-Pressure Boundary of Hydrate Formation in the Carbon Dioxide−Water System

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.

Hydrostatic Pressure-Induced Phase Transitions in Rb2KInF6 and Rb2KScF6 Crystals: Raman Spectra and Lattice Dynamics Simulations

Raman scattering spectra of Rb2KInF6 and Rb2KScF6 crystals have been studied under hydrostatic pressure up to 5.3 GPa at room temperature. Results are interpreted within semiempirical simulations of the lattice dynamics. Observed phase transitions both in Rb2KInF6 and Rb2KScF6 crystals are associated with condensation of soft F1g phonon mode. High-pressure phases for both crystals are supposed to be of C2/m space group.

Non-hydrostatic compression of zeolite NaA in water medium: connection to anomalous conductivity

Abstract 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 H2O 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.

In situ observation of amorphous-amorphous apparently first-order phase transition in zeolites

In this letter, the authors present the observation of the phase transition between low-density amorphous (LDA) and high-density amorphous (HDA) zeolites using a high pressure Raman spectroscopy. It is found that this transition is apparently of the first order and occurs with a silicon coordination rise. It is shown that the Raman spectra of the LDA-HDA phase transitions in zeolites and in silicon are almost identical, suggesting a generality of amorphous-amorphous transformations both in simple substances and in complex polyatomic materials with tetrahedral configurations.

Role of internal pressure in a ferroelastic phase transition

It is shown that the driving force of a ferroelastic phase transition is internal pressure. The pressure gives rise to symmetric deformation, whose energy accumulates as pressure increases and, at the phase transition point, is partially transferred into the energy of antisymmetric deformations.

Pressure-Induced Phase Transitions in RbMnCl3 Crystal—Raman Spectra and Lattice Dynamics

Raman scattering spectra of RbMnCl 3 crystal has been studied at ambient conditions and under high hydrostatic pressure. Results are interpreted within abinitio lattice dynamics approach. Experimental results agree rather well with numerical simulations at the lower frequencies range, while a bit worse—for higher frequency modes. The first transition was observed at 0.7 GPa in good agreement with earlier measurements, and spectral transformation agrees with transition to the perovskite cubic phase predicted theoretically. New transitions were found at 1.1 GPa and 5 GPa, presumably—to distorted cubic phases.

Raman spectra of shortite Na 2 Ca 2 (CO 3 ) 3 compressed up to 8 GPa

ABSTRACT 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.

Effect of high pressure/low temperature on cysteine, its salts and derivatives

Effect of high-pressure / low temperature on cysteine, its salts and derivatives Vasily S. Minkov,a,b Boris A. Kolesov,a,c Sergey V. Goryainov,a,d Valery A. Drebushchak,a,d Tatyana N. Drebushchak,a,b Andrey G. Ogienko,a,c Elena V. Boldyreva,a,b aREC-008 Novosibirsk State University (Russian Federation). bInstitute of Solid State Chemistry and Mechanochemistry SB RAS (Russian Federation). cInstitute of Inorganic Chemistry SB RAS (Russian Federation). dInstitute of Geology and Mineralogy SB RAS Novosibirsk, (Russian Federation). E-mail: vasilyminkov@yahoo.com