The iron-57 Mössbauer spectra of YCoFe 3B have been measured between 4.2 and 480 K and reveal tha... more The iron-57 Mössbauer spectra of YCoFe 3B have been measured between 4.2 and 480 K and reveal that YCoFe 3B exhibits an axial orientation of the iron magneti c moments below 450 K and a basal orientation above 4 50 K. This spin reorientation, also observed in the thermomagnetic curves, results from the different signs of the contributions to the magnetic anisotropy of the 2 c and 6i sites that are occupied by iron. The neutron diffraction patterns of YCoFe 3B have been measured at 2 K and between 290 and 770 K and have been successfully an alysed with a model compatible with the magnetic orientation obtained f rom the Mössbauer spectra. The hybridization between the cobalt or iron 3 d orbitals and the boron 2 p orbitals leads to a larger magnetic moment and hyperfine field on the 2c site as compared to the 6 i
Conductive metal-organic frameworks are an emerging class of three-dimensional architectures with... more Conductive metal-organic frameworks are an emerging class of three-dimensional architectures with degrees of modularity, synthetic flexibility and structural predictability that are unprecedented in other porous materials. However, engendering long-range charge delocalization and establishing synthetic strategies that are broadly applicable to the diverse range of structures encountered for this class of materials remain challenging. Here, we report the synthesis of K Fe(BDP) (0 ≤ x ≤ 2; BDP = 1,4-benzenedipyrazolate), which exhibits full charge delocalization within the parent framework and charge mobilities comparable to technologically relevant polymers and ceramics. Through a battery of spectroscopic methods, computational techniques and single-microcrystal field-effect transistor measurements, we demonstrate that fractional reduction of Fe(BDP) results in a metal-organic framework that displays a nearly 10,000-fold enhancement in conductivity along a single crystallographic axi...
The type-I filled germanium clathrates contain ``rattling" atoms... more The type-I filled germanium clathrates contain ``rattling" atoms in two oversized atomic cages, a rattling that provides the phonon glass behavior required for efficient thermoelectric materials. For the Sr and Eu filled clathrates, the guests in the larger cage are located off-center on four subsites, and a jump model between these subsites was proposed to explain their glass-like thermal conductivity.
ABSTRACTIn the filled gallium-germanium clathrates, R8Ga16Ge30, where R is Ba, Sr, or Eu, the gue... more ABSTRACTIn the filled gallium-germanium clathrates, R8Ga16Ge30, where R is Ba, Sr, or Eu, the guests are located in two large cages and are weakly bound to the crystalline clathrate framework. The caged guests exhibit a localized “rattling” vibrational mode that provides an efficient mechanism for reducing the thermal conductivity. Inelastic neutron scattering and nuclear inelastic scattering measurements have yielded the phonon density of states in R8Ga16Ge30; the line width of the localized vibrational modes is found to be an important parameter in determining the lattice thermal conductivity. Neutron diffraction studies on R8Ga16Ge30 have shown that the guests in the larger cage are located off-center, and it was proposed that their jumping about the four off-center locations is responsible for the observed glass-like thermal conductivity at temperatures below 10 K. The detection of such slow guest motion is challenging because the typical time and energy scales involved are ca. ...
The iron-57 Mössbauer spectra of YCoFe 3B have been measured between 4.2 and 480 K and reveal tha... more The iron-57 Mössbauer spectra of YCoFe 3B have been measured between 4.2 and 480 K and reveal that YCoFe 3B exhibits an axial orientation of the iron magneti c moments below 450 K and a basal orientation above 4 50 K. This spin reorientation, also observed in the thermomagnetic curves, results from the different signs of the contributions to the magnetic anisotropy of the 2 c and 6i sites that are occupied by iron. The neutron diffraction patterns of YCoFe 3B have been measured at 2 K and between 290 and 770 K and have been successfully an alysed with a model compatible with the magnetic orientation obtained f rom the Mössbauer spectra. The hybridization between the cobalt or iron 3 d orbitals and the boron 2 p orbitals leads to a larger magnetic moment and hyperfine field on the 2c site as compared to the 6 i
Conductive metal-organic frameworks are an emerging class of three-dimensional architectures with... more Conductive metal-organic frameworks are an emerging class of three-dimensional architectures with degrees of modularity, synthetic flexibility and structural predictability that are unprecedented in other porous materials. However, engendering long-range charge delocalization and establishing synthetic strategies that are broadly applicable to the diverse range of structures encountered for this class of materials remain challenging. Here, we report the synthesis of K Fe(BDP) (0 ≤ x ≤ 2; BDP = 1,4-benzenedipyrazolate), which exhibits full charge delocalization within the parent framework and charge mobilities comparable to technologically relevant polymers and ceramics. Through a battery of spectroscopic methods, computational techniques and single-microcrystal field-effect transistor measurements, we demonstrate that fractional reduction of Fe(BDP) results in a metal-organic framework that displays a nearly 10,000-fold enhancement in conductivity along a single crystallographic axi...
The type-I filled germanium clathrates contain ``rattling" atoms... more The type-I filled germanium clathrates contain ``rattling" atoms in two oversized atomic cages, a rattling that provides the phonon glass behavior required for efficient thermoelectric materials. For the Sr and Eu filled clathrates, the guests in the larger cage are located off-center on four subsites, and a jump model between these subsites was proposed to explain their glass-like thermal conductivity.
ABSTRACTIn the filled gallium-germanium clathrates, R8Ga16Ge30, where R is Ba, Sr, or Eu, the gue... more ABSTRACTIn the filled gallium-germanium clathrates, R8Ga16Ge30, where R is Ba, Sr, or Eu, the guests are located in two large cages and are weakly bound to the crystalline clathrate framework. The caged guests exhibit a localized “rattling” vibrational mode that provides an efficient mechanism for reducing the thermal conductivity. Inelastic neutron scattering and nuclear inelastic scattering measurements have yielded the phonon density of states in R8Ga16Ge30; the line width of the localized vibrational modes is found to be an important parameter in determining the lattice thermal conductivity. Neutron diffraction studies on R8Ga16Ge30 have shown that the guests in the larger cage are located off-center, and it was proposed that their jumping about the four off-center locations is responsible for the observed glass-like thermal conductivity at temperatures below 10 K. The detection of such slow guest motion is challenging because the typical time and energy scales involved are ca. ...
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Papers by Gary Long