S. Heathman | European Commission (original) (raw)
Papers by S. Heathman
Physica B: Condensed Matter, 2005
Journal of Nuclear Science and Technology, 2002
MRS Proceedings, 2003
ABSTRACT One effect of pressure on elements and compounds is to decease their interatomic distanc... more ABSTRACT One effect of pressure on elements and compounds is to decease their interatomic distances, which can bring about dramatic perturbations in their electronic nature and bonding, which can be reflected in changes in physical and/or chemical properties. One important issue in the actinide series of elements is the effect of pressure on the 5f-electrons. We have probed changes in electronic behavior with pressure by monitoring structure by X-ray diffraction, and have studied several actinide metals and compounds from thorium through einsteinium. These studies have employed angle dispersive diffraction using synchrotron radiation, and energy dispersive techniques via conventional X-ray sources. The 5f-electrons of actinide metals and their alloys are often affected significantly by pressure, while with compounds, the structural changes are often not linked to the involvement of 5 f-electron. We shall present some of our more recent findings from studies of selected actinide metals, alloys and compounds under pressure. A discussion of the results in terms of the changes in electronic configurations and bonding with regard to the element's position in the series is also addressed.
Physica B: Condensed Matter, 1997
Physical Review B, 2003
ABSTRACT The structural behavior of α-uranium at room temperature has been studied up to 100 GPa ... more ABSTRACT The structural behavior of α-uranium at room temperature has been studied up to 100 GPa in diamond anvil cells using angle-dispersive x-ray diffraction at a synchrotron source. The orthorhombic Cmcm structure is stable to at least 100 GPa. We present details of the variation of all structural parameters, derived from Rietveld analysis of the diffraction patterns: the lattice parameters a, b, and c, and the positional parameter y, as a function of pressure. Precise data, as well as the use of different media for the pressure transmission, allow us to question previous values of several parameters deduced by x-ray diffraction, especially the bulk modulus, and we obtain a revised bulk modulus of B0=104(2)GPa with B0′=6.2(2). We have also performed accurate (zero-temperature) electronic structure calculations with full structural relaxation up to 100 GPa to test theory against our experimental results. The magnitude and trends of the calculated structural parameters are in reasonable agreement with experiment. In contrast, our bulk modulus calculated at our zero-pressure volume is B0=136GPa and B0′=5.07, in agreement with previous calculations, differing markedly from experimental values.
Journal of the Less Common Metals, 1990
ABSTRACT
Physical Review B, 1996
ABSTRACT
Physical Review B, 2003
ABSTRACT Protactinium occupies an important position in the actinide series of elements, as it re... more ABSTRACT Protactinium occupies an important position in the actinide series of elements, as it represents the first of four elements (Pa-Pu) having 5f-electron character in their bonding at atmospheric pressure. We have determined in experimental studies with synchrotron radiation to 130 GPa, that the tetragonal structure of protactinium (space group I4/mmm) converts to an orthorhombic, alpha-uranium structure (space group Cmcm) at 77(5) GPa, where the atomic volume has been reduced by ∼30%. This structural change is interpreted as reflecting an increase in 5f-electron contribution to the bonding in protactinium over that initially present, becoming more similar to that present in alpha-uranium metal at atmospheric pressure. We determined experimentally that this structural transformation occurred at significantly higher pressures and at a smaller atomic volume than predicted by theory. The experimental results reported here represent the highest pressures under which protactinium metal has been studied.
Physical Review B, 2003
ABSTRACT
Journal of Physics: Condensed Matter, 2002
ABSTRACT X-ray diffraction measurements under pressure have been performed on seven different com... more ABSTRACT X-ray diffraction measurements under pressure have been performed on seven different compositions in the UxLa1−xS system (x = 0, 0.08, 0.40, 0.50, 0.60, 0.80, 1). All the compounds have the same structure (NaCl type) at ambient pressure, but show different behaviours under pressure. A transformation into the CsCl-type structure is only observed for x ≤ 0.60. For x = 0.80 and 1, the high-pressure phase has yet to be determined. We also observe a difference in bulk modulus (for x ≤ 0.50, B0 ≤ 90 GPa whereas for x ≥ 0.60, B0 ~ 100 GPa) and in the transition pressure (~30 GPa for low-uranium-content compounds and from 45 to 80 GPa for high concentrations).
Journal of Physics: Condensed Matter, 2013
The structural behaviour under compression of different lanthanide (La, Gd, Ho, Yb) and actinide ... more The structural behaviour under compression of different lanthanide (La, Gd, Ho, Yb) and actinide (Am) monochalcogenides is studied by means of in situ high-pressure x-ray diffraction. All the investigated compounds crystallize at ambient conditions within a cubic (B1) NaCl-type structure but show different behaviours at high pressures. LaTe and AmTe undergo B1 to B2 (CsCl-type structure) phase transitions, starting at 9 GPa and 12 GPa, respectively. The high-pressure phase of AmTe exhibits an electronic transition, identified by an anomaly in the compression curve which is accompanied by a sample colour change. The other three monochalcogenides studied here show clear evidence of decomposition and amorphization under pressure and are, to the best of our knowledge, the first in the LnTe series to show a pressure-induced amorphization. The bulk moduli of all B1-type structure compounds are calculated using the third-order Birch-Murnaghan equation of state.
Journal of Nuclear Materials, 1989
ABSTRACT
Journal of Magnetism and Magnetic Materials, 2004
ABSTRACT
Physica B: Condensed Matter, 2005
Journal of Nuclear Science and Technology, 2002
MRS Proceedings, 2003
ABSTRACT One effect of pressure on elements and compounds is to decease their interatomic distanc... more ABSTRACT One effect of pressure on elements and compounds is to decease their interatomic distances, which can bring about dramatic perturbations in their electronic nature and bonding, which can be reflected in changes in physical and/or chemical properties. One important issue in the actinide series of elements is the effect of pressure on the 5f-electrons. We have probed changes in electronic behavior with pressure by monitoring structure by X-ray diffraction, and have studied several actinide metals and compounds from thorium through einsteinium. These studies have employed angle dispersive diffraction using synchrotron radiation, and energy dispersive techniques via conventional X-ray sources. The 5f-electrons of actinide metals and their alloys are often affected significantly by pressure, while with compounds, the structural changes are often not linked to the involvement of 5 f-electron. We shall present some of our more recent findings from studies of selected actinide metals, alloys and compounds under pressure. A discussion of the results in terms of the changes in electronic configurations and bonding with regard to the element's position in the series is also addressed.
Physica B: Condensed Matter, 1997
Physical Review B, 2003
ABSTRACT The structural behavior of α-uranium at room temperature has been studied up to 100 GPa ... more ABSTRACT The structural behavior of α-uranium at room temperature has been studied up to 100 GPa in diamond anvil cells using angle-dispersive x-ray diffraction at a synchrotron source. The orthorhombic Cmcm structure is stable to at least 100 GPa. We present details of the variation of all structural parameters, derived from Rietveld analysis of the diffraction patterns: the lattice parameters a, b, and c, and the positional parameter y, as a function of pressure. Precise data, as well as the use of different media for the pressure transmission, allow us to question previous values of several parameters deduced by x-ray diffraction, especially the bulk modulus, and we obtain a revised bulk modulus of B0=104(2)GPa with B0′=6.2(2). We have also performed accurate (zero-temperature) electronic structure calculations with full structural relaxation up to 100 GPa to test theory against our experimental results. The magnitude and trends of the calculated structural parameters are in reasonable agreement with experiment. In contrast, our bulk modulus calculated at our zero-pressure volume is B0=136GPa and B0′=5.07, in agreement with previous calculations, differing markedly from experimental values.
Journal of the Less Common Metals, 1990
ABSTRACT
Physical Review B, 1996
ABSTRACT
Physical Review B, 2003
ABSTRACT Protactinium occupies an important position in the actinide series of elements, as it re... more ABSTRACT Protactinium occupies an important position in the actinide series of elements, as it represents the first of four elements (Pa-Pu) having 5f-electron character in their bonding at atmospheric pressure. We have determined in experimental studies with synchrotron radiation to 130 GPa, that the tetragonal structure of protactinium (space group I4/mmm) converts to an orthorhombic, alpha-uranium structure (space group Cmcm) at 77(5) GPa, where the atomic volume has been reduced by ∼30%. This structural change is interpreted as reflecting an increase in 5f-electron contribution to the bonding in protactinium over that initially present, becoming more similar to that present in alpha-uranium metal at atmospheric pressure. We determined experimentally that this structural transformation occurred at significantly higher pressures and at a smaller atomic volume than predicted by theory. The experimental results reported here represent the highest pressures under which protactinium metal has been studied.
Physical Review B, 2003
ABSTRACT
Journal of Physics: Condensed Matter, 2002
ABSTRACT X-ray diffraction measurements under pressure have been performed on seven different com... more ABSTRACT X-ray diffraction measurements under pressure have been performed on seven different compositions in the UxLa1−xS system (x = 0, 0.08, 0.40, 0.50, 0.60, 0.80, 1). All the compounds have the same structure (NaCl type) at ambient pressure, but show different behaviours under pressure. A transformation into the CsCl-type structure is only observed for x ≤ 0.60. For x = 0.80 and 1, the high-pressure phase has yet to be determined. We also observe a difference in bulk modulus (for x ≤ 0.50, B0 ≤ 90 GPa whereas for x ≥ 0.60, B0 ~ 100 GPa) and in the transition pressure (~30 GPa for low-uranium-content compounds and from 45 to 80 GPa for high concentrations).
Journal of Physics: Condensed Matter, 2013
The structural behaviour under compression of different lanthanide (La, Gd, Ho, Yb) and actinide ... more The structural behaviour under compression of different lanthanide (La, Gd, Ho, Yb) and actinide (Am) monochalcogenides is studied by means of in situ high-pressure x-ray diffraction. All the investigated compounds crystallize at ambient conditions within a cubic (B1) NaCl-type structure but show different behaviours at high pressures. LaTe and AmTe undergo B1 to B2 (CsCl-type structure) phase transitions, starting at 9 GPa and 12 GPa, respectively. The high-pressure phase of AmTe exhibits an electronic transition, identified by an anomaly in the compression curve which is accompanied by a sample colour change. The other three monochalcogenides studied here show clear evidence of decomposition and amorphization under pressure and are, to the best of our knowledge, the first in the LnTe series to show a pressure-induced amorphization. The bulk moduli of all B1-type structure compounds are calculated using the third-order Birch-Murnaghan equation of state.
Journal of Nuclear Materials, 1989
ABSTRACT
Journal of Magnetism and Magnetic Materials, 2004
ABSTRACT