An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The effect of pressure on the acoustic modes and adiabatic elastic constants of the perovskite-type ($AB$O${}_{3}$) relaxor compound PbSc${}_{1/2}$Ta${}_{1/2}$O${}_{3}$ have been studied by Brillouin spectroscopy at room temperature up to 9.2 GPa. It is shown that the elastic constants are very sensitive to the pressure-induced structural transformations that were established by diffraction and Raman scattering analysis. Changes in the evolution of the pseudocubic elastic constants ${c}_{11}$ and ${c}_{44}$ occur at the two phase-transition pressures ${p}_{c}$${}_{1}$ $=$ 1.9 GPa and ${p}_{c2}$ \ensuremath{\sim} 5.5 GPa. Changes in evolution of ${c}_{12}$ occur at the two characteristic pressures ${p}_{1}$${}^{*}$ $=$ 1.2 GPa and ${p}_{2}$${}^{*}$ \ensuremath{\sim} 3.0 GPa, which mark changes in the local structure that precede the corresponding phase transitions. The elastic anisotropy and the width of the transverse acoustic mode increase in the pressure range between ${p}_{c}$${}_{1}$ and ${p}_{c}$${}_{2}$ with a maximum near ${p}_{2}$${}^{*}$. A strong decrease in the Cauchy parameter is observed at pressures above ${p}_{2}$${}^{*}$, which indicates an enhancement of the covalent character of chemical bonding. Increasing pressure gradually suppresses the central peak typical of the relaxor ergodic state, and the quasielastic scattering vanishes at a pressure slightly above ${p}_{2}$${}^{*}$.
Mineral inclusions entrapped in other minerals may record the local stresses at the moment of their entrapment in the deep Earth. When rocks are exhumed to the surface of the Earth, residual stresses and strains may still be preserved in the inclusion. If measured and interpreted correctly through elastic geobarometry, they give us invaluable information on the pressures (P) and temperatures (T) of metamorphism. Current estimates of P and T of entrapment rely on simplified models that assumes that the inclusion is spherical and embedded in an infinite host, and that their elastic properties are isotropic. We report a new method for elastic geobarometry for anisotropic inclusions in quasi-isotropic hosts. The change of strain in the inclusion is modelled with the axial equations of state of the host and the inclusion. Their elastic interaction is accounted for by introducing a 4th rank tensor, the relaxation tensor, that can be evaluated numerically for any symmetry of the host and the inclusion and for any geometry of the system. This approach can be used to predict the residual strain/stress state developed in an inclusion after exhumation from known entrapment conditions, or to estimate the entrapment conditions from the residual strain measured in real inclusions. In general, anisotropic strain and stress states are developed in non-cubic mineral inclusions such as quartz and zircon, with deviatoric stresses typically limited to few kbars. For garnet hosts, the effect of the mutual crystallographic orientation between the host and the inclusion on the residual strain and stress is negligible when the inclusion is spherical and isolated. Assuming external hydrostatic conditions, our results suggest that the isotropic and the new anisotropic models give estimations of entrapment conditions within 2%.
AbstractA series of model perovskite-type relaxor ferroelectrics (pure and A-/B-site doped PbSc1/2Ta1/2O3 and PbSc1/2Nb1/2O3 as well as of 0.9PbZn1/3Nb2/3O3−0.1PbTiO3) were studied by high pressure diffraction and inelastic light scattering in order to elucidate the mesoscopic-scale ferroic atomic arrangements responsible for the superb macroscopic properties of these materials. The combined analysis of the pressure-enhanced phonon anomalies observed by Raman spectroscopy and the pressure-induced long-range order detected by synchrotron X-ray and neutron diffraction revealed that at ambient conditions antiferrodistortive order coexists with the ferroelectric order on the mesoscopic scale. This suggests that the locally polarized spatial nanoregions known as polar nanoregions are ferrielectric in nature and their abundance and mean size depend on both the antiferrodistortive and ferroelectric coupling, which in turn can be tuned by appropriate chemical variations.Keywords: relaxor ferroelectricsX-ray diffractionRaman spectroscopyperovskitesphase transitions AcknowledgementsFinancial support by the Deutsche Forschungsgemeinschaft (SPP 1236, projects MI 1127/2-1 and MI1127/2-2) is gratefully acknowledged. The DFG-priority project SPP1236 was funded by the Deutsche Forschungsgemeinschaft from 2006 to 2013. The authors thank Marin Gospodinov, Bulgarian Academy of Sciences, for synthesizing the single-crystal samples, Carsten Paulmann and William G. Marshall for the excellent support at F1/DESY and Pearl/ISIS, respectively, Jing Zhao, Virginia Tech, for help in high-precision single-crystal XRD data collection, Claude Ederer, Trinity College Dublin, for DFT calculations, and Hauke Marquardt and Sergio Speziale, GFZ Potsdam, for the collaborative Brillouin spectroscopic study. The authors are also grateful to Björn Winkler, Goethe-Universität Frankfurt, for the opportunity to use the gas loader available in his lab.Notes†This contribution is part of the final report summarizing the results of the DFG-priority project SPP1236, which was funded by the Deutsche Forschungsgemeinschaft from 2006–2013.
Elastic geobarometry makes use of the contrast in elastic proprieties between host and inclusion crystals to determine the entrapment conditions of the inclusions from the residual stress and strain measured in the inclusion when its host is at ambient conditions. The theoretical basis has been developed extensively in the past few years, but an experimental validation of the method is still required. We performed two syntheses experiments with quartz inclusions in pure almandine garnet at eclogitic conditions. Experiment labelled Alm-1 with synthesis performed at P = 3.0 GPa and T = 775 °C and Alm-2 at P = 2.5 GPa and T = 800 °C. All the experiments have been carried out in a piston-cylinder press. Isolated, fully-enclosed quartz inclusions in the recovered garnets have been then measured using micro-Raman spectroscopy. All fully-buried inclusions exhibit Raman peaks at higher frequencies and wavenumbers than those obtained from quartz crystals at ambient pressure. If these peak shifts are interpreted as a remnant pressures by use of hydrostatic calibrations of the Raman shifts of quartz with pressure, the remnant pressures show a large spread in values and lead to significant errors in back-calculated entrapment pressures, of up to 1.4 GPa for inclusions synthesised at 3.0 GPa. These results confirm that quartz inclusions trapped inside garnet are not subject to hydrostatic pressure. We therefore used the phonon-mode Grüneisen tensors of quartz to calculate the full strain state of each inclusion, from which the full anisotropic stress state can be calculated by using the elastic properties of quartz. The mean residual remnant stress of the inclusions determined in this way show a much smaller spread in values. Entrapment pressures calculated from this mean stress with the isotropic model for host-inclusion systems differ from the known experimental values by <0.2 GPa, which is of the order of the combined experimental uncertainties. These results show that the most significant effect of the elastic anisotropy of quartz is on the Raman shifts of the inclusion, and not on the subsequent calculation of entrapment conditions.
Ba 3 CaCuSi 6 O 17 cristallise dans B2mb avec a=14,405, b=16,077, c=7,088 A, Z=4; affinement jusqu'a R=0,050. Formation des cristaux comme etant un sous-produit de la synthese des supraconducteurs Tl−Cu−Ca−Ba. La structure consiste en des tetraedres SiO 4 de sommets communs et formant des cycles deformes a 6 chainons, qui a leur tour sont lies par deux coins aux autres cycles pour former des chaines de cycles a 6 chainons. Les sites des atomes Ca et Ba sont coordonnes 8 fois et celui du Cu est plan carre
The single-crystal X-ray structure of Ru(3)(CO)(12) is reported at 8 pressures ranging from 1 atm (0.0 GPa) to 8.14(5) GPa. Although intramolecular bonding parameters remain relatively constant, intramolecular and intermolecular nonbonding contact distances decrease by an average of 4% and 15%, respectively. At 8.14 GPa, O...O, C...O, and C...C intermolecular distances as short as 2.54(4), 2.64(6), and 3.07(4) A, respectively, are observed, and the unit cell compresses to 75% of the ambient pressure volume. Raman and infrared spectroscopic measurements show that carbonyl stretching frequencies shift to higher wavenumber values by as much as 80 cm(-)(1), even though Ru-C and C-O distances stay roughly constant throughout the entire pressure range studied. Compression of the sample to above 18 GPa with laser radiation results in an irreversible transformation due to either decomposition or a total collapse of D(3)(h) molecular geometry accompanied by color darkening.
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