The High-Temperature Phonon Anomalies of α-uranium.

MRS Proceedings ◽

10.1557/opl.2012.894 ◽

2012 ◽

Vol 1444 ◽

Author(s):

Peter S. Riseborough

Keyword(s):

High Temperature ◽

Fermi Energy ◽

Heavy Fermion ◽

Electronic Energy ◽

High Temperature Phase ◽

Energy Scale ◽

Temperature Phase ◽

Resonant Coupling ◽

Heavy Fermion Materials ◽

Increasing Temperature

ABSTRACTThere is a growing body of evidence that a number of mixed-valent and heavy-fermion materials show renormalized hybridization gaps either at the Fermi-energy or close to the Fermi-energy. In the former case, a heavy-fermion semiconducting state occurs and in the later case, the system remains metallic at low temperatures. The magnitudes of the hy-bridization gaps are observed to decrease with increasing temperature. The existence of a low-energy electronic energy scale creates a possibility that the Born-Oppenheimer ap-proximation may fail and that there may be a resonant coupling between the phonons and the electronic excitations. Here we argue that such a mechanism may be the cause of the phonon anomalies observed in neutron scattering experiments on the high-temperature phase of alpha-uranium.

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Short-range ordering of vacancies and Fermi surface of TiO

Acta Crystallographica Section A ◽

10.1107/s0567739471000834 ◽

1971 ◽

Vol 27 (4) ◽

pp. 376-383 ◽

Cited By ~ 53

Author(s):

J. R. Castles ◽

J. M. Cowley ◽

A. E. C. Spargo

Keyword(s):

High Temperature ◽

Fermi Surface ◽

Diffuse Scattering ◽

Short Range ◽

Direct Relationship ◽

Electronic Energy ◽

High Temperature Phase ◽

Titanium Monoxide ◽

Temperature Phase ◽

Short Range Ordering

The structure of the disordered (high-temperature) phase of titanium monoxide has been studied by electron diffraction. Composition-dependent complex distributions of diffuse scattering are observed and interpreted in terms of short-range-ordered configurations of lattice vacancies. The proposition that the form of the diffuse scattering may correspond to ordering under the influence of long-range electronic energy terms and so show a direct relationship to the topology of the Fermi surface is examined.

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Anisotropic thermal expansion in yttrium silicate

Journal of Materials Research ◽

10.1557/jmr.2003.0236 ◽

2003 ◽

Vol 18 (7) ◽

pp. 1715-1722 ◽

Cited By ~ 23

Author(s):

Koichiro Fukuda ◽

Hiroyuki Matsubara

Keyword(s):

Thermal Expansion ◽

High Temperature ◽

Phase Space ◽

Linear Thermal Expansion ◽

High Temperature Phase ◽

Acute Angle ◽

Temperature Phase ◽

Space Group ◽

Anisotropic Thermal Expansion ◽

Increasing Temperature

In this study, crystals of Y2SiO5 were examined by high-temperature powder x-ray diffractometry to determine the changes in unit-cell dimensions with temperatures up to 1273 K for the X1 phase (the low-temperature phase, space group P121/c1) and 1473 K for the X2 phase (the high-temperature phase, space group I12/a1). The lattice deformations of both phases induced by thermal expansion were investigated by matrix algebra analysis to determine the directions and magnitudes of the principal distortions (λi, i = 1, 2, and 3). For the X1 phase, λ1 and λ2 invariably showed a positive thermal expansion. On the other hand, λ3 showed a negative thermal expansion below 1173 K; the maximum contraction of 0.10(4)% occurred at 685 K. The λ2 axis invariably coincides with the crystallographic b axis. The directions of λ1 and λ3, defined by the acute angle λ3 ^ c changed between 53(3)° (T = 394 K) and 45(1)° (T = 788 K). For the X2 phase, all of the principal distortions steadily increased with increasing temperature. The angle λ3 ^ c steadily decreased from 71(2)° to 62.1(1)° with increasing temperature. The mean linear thermal expansion coefficients were, when compared at the same temperatures, necessarily higher for the X1 phase than for the X2 phase. The lattice change of X1–RE2SiO5 (RE = Y and Yb–La), which was induced by the substitution of rare-earth (RE) ions, showed a striking resemblance with the lattice deformation of X1-Y2SiO5, which was caused by the thermal expansion. Because the lattice change of the former must be caused by the isotropic expansion of the RE sites, the anisotropic thermal expansion of the latter would be essentially attributable to the isotropic thermal expansion of the YO9 and YO7 polyhedron.

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SU(2NF) symmetry of confinement in QCD and its observation at high temperature.

EPJ Web of Conferences ◽

10.1051/epjconf/201818202046 ◽

2018 ◽

Vol 182 ◽

pp. 02046 ◽

Cited By ~ 1

Author(s):

L.Ya. Glozman

Keyword(s):

High Temperature ◽

Dirac Operator ◽

Magnetic Interaction ◽

High Temperature Phase ◽

Temperature Phase ◽

Zero Modes ◽

Left Handed ◽

Electric Interaction ◽

The Right ◽

Increasing Temperature

In this talk we first overview lattice results that have led to the observation of new SU(2)CS and SU(2NF) symmetries upon artificial truncation of the near-zero modes of the Dirac operator at zero temperatute and at high temperature without any truncation. These symmetries are larger than the chiral symmetry of the QCD Lagrangian and contain chiral symmetries SU(NF)L x SU(NF)R and U(1)A as subgroups. In addition to the standard chiral transformations the SU(2)CS and SU(2NF) transformations mix the right- and left-handed components of the quark fields. It is a symmetry of the confining chromo-electric interaction while the chromo-magnetic interaction manifestly breaks it. Emergence of these symmetries upon truncation of the near-zero modes of the Dirac operator at T=0 means that all effects of the chromo-magnetic interaction are located exclusively in the near-zero modes, while confining chromo-electric interaction is distributed among all modes. Appearance of these symmetries at high T, where the temperature suppresses the near-zero modes, has radical implications because these symmetries are incompatible with the asymptotically free deconfined quarks at increasing temperature. The elementary objects in the high-temperature phase of QCD should be quarks bound by the pure chromo-electric field that is not accompanied by the chromo-magnetic effects.

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Nuclear magnetic resonance investigations of the structural phase transitions of AlPO4 tridymite

Journal of Materials Research ◽

10.1557/jmr.1995.2586 ◽

1995 ◽

Vol 10 (10) ◽

pp. 2586-2591 ◽

Cited By ~ 3

Author(s):

Yuehui Xiao ◽

R. James Kirkpatrick

Keyword(s):

High Temperature ◽

Bond Angle ◽

Structural Phase ◽

Local Symmetry ◽

Quadrupole Coupling Constant ◽

High Temperature Phase ◽

Temperature Phase ◽

Temperature Structure ◽

Bond Angles ◽

Increasing Temperature

27Al and 31P NMR spectroscopic data are presented for the tridymite polymorph of AlPO4 (AlPO4−1) through its structural phase transition at about 80 °C. The RT 27Al and 31P spectra of AlPO4−t both contain doublets of broad peaks, indicating two well-separated groups of sites in the RT structure with mean Al-O-P bond angles per tetrahedron of ∼ 147.8°and 153.1°(±1). With increasing temperature, the doublets remain the same up to about 74 °C, where the relative intensities of the two peaks start to change. The peak corresponding to smaller Al-O-P bond angles disappears, and above ∼88 °C the 27Al and 31P spectra contain single symmetrical peaks, corresponding to a mean Al-O-P bond angle of 153.4°. This bond angle increases gradually with increasing temperature to 153.7°at ∼150 °C and remains constant to about 500 °C. 27Al quadrupole echo experiments suggests that the 27Al nuclear quadrupole coupling constant (QCC) is small and decreases with increasing temperature. QCC remains nonzero in the high temperature phase of AlPO4−t, consistent with the previously proposed 3m local symmetry of Al in the high-temperature structure.

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