We report the effect of the crystal field (CF) on the broken symmetry phase transition (BSP) in s... more We report the effect of the crystal field (CF) on the broken symmetry phase transition (BSP) in solid parahydrogen, orthodeuterium, and hydrogen deuteride. The CF was calculated taking into account a distortion from the ideal HCP structure. We find that, in addition to the molecular field generated by the coupling terms in the intermolecular potential, the Hamiltonian of the system contains a crystal-field term, originating from single-molecular terms in the intermolecular potential. Ignoring the CF is the main cause of the systematic underestimation of the transition pressure, characteristic of published theories of the BSP transition. The distortion of the lattice that gives rise to the negative CF in response to the applied pressure is in accord with the general Le Chatelier-Braun principle.
The solid solutions between Fe3O4 and Fe2TiO4 are principal magnetic substance for the rock magne... more The solid solutions between Fe3O4 and Fe2TiO4 are principal magnetic substance for the rock magnetism in the crust. Fe3O4 is ferrimagnetic and Fe2TiO4 is antiferromagnetic. Several models of the cation distribution in Fe3-xTixO4 solid solutions have been proposed. In the present study electron spin states of these solid solutions under high pressures have been investigated by X-ray powder diffraction, X-ray
Very recently a new group promoting High Pressure (HP) research started at the Advanced Photon So... more Very recently a new group promoting High Pressure (HP) research started at the Advanced Photon Source (APS), the High Pressure Synergetic Center (HPSynC). The HPSynC mission is to establish high-pressure environments at many APS beamlines for the users community. This group will be equivalent to a full beamline team of eight scientists/engineers who, working with HP researchers and beamline scientists,
Physics of The Earth and Planetary Interiors, 2011
The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-3... more The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-330 km depth range, has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability. The coesite to stishovite transition of SiOâ matches deeper X-discontinuity depths but requires 5-10% free silica in the mantle to match observed impedance contrast.
The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), ori... more The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), orientational order parameter, and crystal-field parameter in hexagonal close-packed (hcp) lattice of p-H2, o-D2 and n-H2 are calculated using the semi-empirical lattice-dynamic approach. It is shown that the lattice distortion in the J-even species is two order of magnitude smaller compared with that found in n-H2, and n-D2. The difference is due to the splitting of the J-odd rotational levels in the J-even - J-odd mixtures.
High-pressure optical experiments have been performed on midinfrared excitations unique to the la... more High-pressure optical experiments have been performed on midinfrared excitations unique to the layered cuprates, yet whose physical origin has been unresolved. Measurements of high-pressure midinfrared spectra of Sr2CuCl2o2 unambiguously identify the ~2800-cm-1 absorption as an unusual quasibound two-magnon + phonon excitation. We further show that the broad peak centered near ~4000 cm-1 is a four-magnon + phonon excitation, with spectral
Description/Abstract This project is conducting fundamental studies of inorganic H2 clathrates (H... more Description/Abstract This project is conducting fundamental studies of inorganic H2 clathrates (H2O-and CH4-based). Insights gained from these studies could be applied toward the design and synthesis of hydrogen storage materials that meet the DOE 2010 ...
We report measurements of the oxygen isotope effect in BiSrCa{sub n-1}Cu{sub n}O{sub 2n+4+} (n=1,... more We report measurements of the oxygen isotope effect in BiSrCa{sub n-1}Cu{sub n}O{sub 2n+4+} (n=1, 2,3) single crystals. For optimally doped materials the isotope exponent is found to decrease with increasing the number of CuO2 layers in a manner of inversely correlating with the superconducting transition temperature in this homologous family. This behavior is in contrast to the general belief that the isotope effect can be negligible for the optimally doped cuprates. Our results highlight the important role played by phonons and interlayer coupling in the high-temperature superconductivity.
We report the effect of the crystal field (CF) on the broken symmetry phase transition (BSP) in s... more We report the effect of the crystal field (CF) on the broken symmetry phase transition (BSP) in solid parahydrogen, orthodeuterium, and hydrogen deuteride. The CF was calculated taking into account a distortion from the ideal HCP structure. We find that, in addition to the molecular field generated by the coupling terms in the intermolecular potential, the Hamiltonian of the system contains a crystal-field term, originating from single-molecular terms in the intermolecular potential. Ignoring the CF is the main cause of the systematic underestimation of the transition pressure, characteristic of published theories of the BSP transition. The distortion of the lattice that gives rise to the negative CF in response to the applied pressure is in accord with the general Le Chatelier-Braun principle.
The solid solutions between Fe3O4 and Fe2TiO4 are principal magnetic substance for the rock magne... more The solid solutions between Fe3O4 and Fe2TiO4 are principal magnetic substance for the rock magnetism in the crust. Fe3O4 is ferrimagnetic and Fe2TiO4 is antiferromagnetic. Several models of the cation distribution in Fe3-xTixO4 solid solutions have been proposed. In the present study electron spin states of these solid solutions under high pressures have been investigated by X-ray powder diffraction, X-ray
Very recently a new group promoting High Pressure (HP) research started at the Advanced Photon So... more Very recently a new group promoting High Pressure (HP) research started at the Advanced Photon Source (APS), the High Pressure Synergetic Center (HPSynC). The HPSynC mission is to establish high-pressure environments at many APS beamlines for the users community. This group will be equivalent to a full beamline team of eight scientists/engineers who, working with HP researchers and beamline scientists,
Physics of The Earth and Planetary Interiors, 2011
The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-3... more The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-330 km depth range, has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability. The coesite to stishovite transition of SiOâ matches deeper X-discontinuity depths but requires 5-10% free silica in the mantle to match observed impedance contrast.
The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), ori... more The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), orientational order parameter, and crystal-field parameter in hexagonal close-packed (hcp) lattice of p-H2, o-D2 and n-H2 are calculated using the semi-empirical lattice-dynamic approach. It is shown that the lattice distortion in the J-even species is two order of magnitude smaller compared with that found in n-H2, and n-D2. The difference is due to the splitting of the J-odd rotational levels in the J-even - J-odd mixtures.
High-pressure optical experiments have been performed on midinfrared excitations unique to the la... more High-pressure optical experiments have been performed on midinfrared excitations unique to the layered cuprates, yet whose physical origin has been unresolved. Measurements of high-pressure midinfrared spectra of Sr2CuCl2o2 unambiguously identify the ~2800-cm-1 absorption as an unusual quasibound two-magnon + phonon excitation. We further show that the broad peak centered near ~4000 cm-1 is a four-magnon + phonon excitation, with spectral
Description/Abstract This project is conducting fundamental studies of inorganic H2 clathrates (H... more Description/Abstract This project is conducting fundamental studies of inorganic H2 clathrates (H2O-and CH4-based). Insights gained from these studies could be applied toward the design and synthesis of hydrogen storage materials that meet the DOE 2010 ...
We report measurements of the oxygen isotope effect in BiSrCa{sub n-1}Cu{sub n}O{sub 2n+4+} (n=1,... more We report measurements of the oxygen isotope effect in BiSrCa{sub n-1}Cu{sub n}O{sub 2n+4+} (n=1, 2,3) single crystals. For optimally doped materials the isotope exponent is found to decrease with increasing the number of CuO2 layers in a manner of inversely correlating with the superconducting transition temperature in this homologous family. This behavior is in contrast to the general belief that the isotope effect can be negligible for the optimally doped cuprates. Our results highlight the important role played by phonons and interlayer coupling in the high-temperature superconductivity.
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