T. Kuribayashi

Pressure dependence of the OH-stretching mode in F-rich natural topaz and topaz-OH

Abstract OH stretching vibration modes for F-rich natural topaz (F-topaz) and for fully hydrated topaz (topaz-OH) synthesized at high pressure, were observed using IR and Raman spectroscopies at pressures up to 30.4 GPa and 17.3 GPa, respectively. In F-topaz, the pressure derivative of the frequency of the OH stretching band observed at 3650 cm-1 at ambient pressure was 0.91(3) cm-1/GPa, which was consistent with the value recently reported by Bradbury and Williams (2003). On the other hand, in topaz-OH, the pressure derivatives of the bands initially at 3599 and 3522 cm-1 were -5.2(2) and -2.56(6) cm-1/GPa, respectively. This contrasting behavior between the two forms of topaz at high pressures suggests that the OH substitution for F in topaz affects the hydrogen-bonding behavior under high pressure.

High-pressure structural study of phase-A, Mg7Si2H6O14 using synchrotron radiation

The specimen used in this study was a single crystal of phase-A Mg6.99Si1.99H6.06O14 synthesized using a multi-anvil apparatus at conditions of 1000°C and 10 GPa. Sets of x-ray diffraction intensities were measured with a single crystal of 60 × 50 × 30 μ m using synchrotron radiation up to 9.4 GPa. The unit-cell parameters observed gave K0 = 105 GPa (assuming that K = 4). With increasing pressure, significant decreases of O–O distances for hydrogen bonds were observed.

Pressure dependence of the hydrogen-bond geometry in topaz-OD from neutron powder diffraction

Abstract The crystal structure of deuterated topaz [topaz-OD; Al2SiO4(OD)2], synthesized at 10 GPa and 800 °C, has been determined using neutron powder diffraction at pressures up to 7.5 GPa. The linear axial compressibilities obtained from regressions of the lattice constants vs. pressure are βa = 1.87(1) × 10-3 GPa-1, βb = 1.71(1) × 10-3 GPa-1, and βc = 2.73(1) × 10-3 GPa-1. The occupancy of the D1 site was found to be greater than that of D2, as shown independently using neutron diffraction and infrared spectra at ambient conditions. A bifurcated hydrogen bond involving the D1 site, O4-D1···O2 and O4- D1···O3, and a trifurcated hydrogen bond involving D2 site, O4-D2···O1, O4-D2···O2, and O4-D2···O4 are proposed for hydrogen-bond donor and acceptor pairs in addition to those reported previously. The observed pressure dependences of the hydrogen-bonding geometry show that these donor and acceptor pairs are classifiable into two types of interaction: (1) those that strengthen as a function of pressure (O4-D1···O3, O4-D2···O2, and O4-D2···O4) and (2) those that weaken (O4-D1···O1 and O4-D2···O1). These results also demonstrate that the reason for the contrasting behavior of the ν(OH) between F-rich natural topaz and topaz-OH are both the cooperative effect, O4-D2···O4-D1···O3, and the increasing Al-O4 distance.

Single-crystal X-ray diffraction study of high-pressure phases of KHCO3

Abstract Monoclinic and triclinic high-pressure phases of KHCO3 were identified using in situ high-pressure single-crystal X-ray analysis. These monoclinic and triclinic phases, designated as phases IV and V, respectively, differ from three previously identified phases: I-III. The lattices of the two phases are superimposed along a*IV = 2 × a*V and hk0 and h0l nets of both phases lie on the same plane, i.e., the (100) plane is common in both lattices in real space. The space group of phase IV is P21/b11 with lattice constants of a = 10.024(3) Å, b = 6.912(5) Å, c = 4.1868(11) Å, α = 115.92(4)°, and V = 260.9(2) Å3. The crystal structure of phase IV, excluding the hydrogen atoms, was successfully determined by direct methods and is isostructural with a cesium hydrogen carbonate CsHCO3

T, 2T and 4T wollastonites derived by the Ge substitution

can be used to perform a two-phase refinement using Jana2006 [6]. Furthermore, domains of the two phases were observed by HT highresolution transmission electron microscopy (TEM) and dark field TEM. The aluminium end-member Ca2Al2O5 shows an isotypic incommensurate structure above 1075(10)K. References [1] Smith, D. K. (1962) Acta Cryst. 15, 1146-1152 [2] Redhammer, G. J., Tippelt, G., Roth, G., Amthauer, G. (2004) Am. Mineral. 89, 405-420 [3] Aggarwal, P. S., Gard, J. A., Glasser, F. P., Biggar, G. M. (1972) Cement Concrete Res. 2, 291-297 [4] Kahlenberg, V., Fischer R. X., Shaw, C. S. J. (2000) Am. Mineral. 85, 1061-1065 [5] Krüger, H., Kahlenberg, V. (2005) Acta Cryst. B61, 656-662 [6] Petricek, V., Dusek, M., Palatinus, L. (2006) Jana2006. Institute of Physics, Prague, Czech Republic

The role of Japanese twin boundary in quartz as a source of Brazil twin

Growth textures and atomic configurations of Japanese twin boundary in quartz were studied by using optical microscopy and computational simulations. Samples from Narushima, Nagasaki Prefecture, Japan were polished, etched by hydro fluoric acid for several minutes, and coated by evaporated silver. From observations by reflection microscopy, hourglass-shaped sectors are found near the composition plane of Japanese twin to have mosaic textures composed of polysynthetic Brazil twin. Especially high concentration of Brazil twin with a repeat scale less than 1 micro meter is observed in a growth sector where composition plane of Japanese twin is a straight {112} plane. Atomic configurations at {112} composition plane of Japanese twin were simulated by using molecular dynamics simulations and the energy minimization method. The initial atomic configurations are two slabs of the bulk crystals and simulations were performed for all the different displacements of slabs. From the simulated structures, the twin displacement vector was determined for each of 10 subtypes of Japanese twin. In the case of Brazil twin, the twin displacement vector is known to be a function of orientation of the composition plane. Therefore, screw dislocations are necessarily present where orientation of Brazil twin boundary changes from one orientation to another. Based on the twin displacement vectors of 10 subtypes of Japanese twin determined in this study, we found that dislocations are also required at stepped boundary of Japanese twin, whereas dislocations are not required where Japanese twin boundaries intersect with Brazil twin boundaries. Observations in this study indicate that {112} composition plane of Japanese twin serves as a source of Brazil twin during the course of crystal growth.

The effects of F-OH replacement on the compression of super hydrous phase B structure

Equimolar cocrystal formation between trimethoprim and sulfamethoxazole by sealed heating methods was carried out. When trimethoprim and sulfamethoxazole were heating at a molar ratio 1:1, new powder X-ray diffraction (PXRD) interferences peaks were observed in addition to PXRD interference peaks of each component. Effect of heating time on trimethoprim-sulfamethoxazole equimolar cocrystal was investigated by using PXRD, diffrential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy. Cocrystal obtained by sealed heating method at temperature 160°C had the same PXRD pattern and DSC thermogram with cocrystal from cocrystallization and melting method. These result indicated that heating could induced the formation of cocrystal.