Concerning the High Pressure Allotropic Modification of Cerium

Lawson, A. W.; Tang, Taiwen

doi:10.1103/physrev.76.301

Cited by 263 publications

(56 citation statements)

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“…8,9 That the 4f electrons play an important role in this transition is clear from the large (80%) and abrupt drop in the magnetic susceptibility at 0.7 GPa, 35 thus supporting the Kondo or Mott-Hubbard models. However, recent results also point to the importance of lattice dynamics in Ce's volume collapse.…”

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confidence: 80%

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Different routes to pressure-induced volume collapse transitions in gadolinium and terbium metals

et al. 2013

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The sudden decrease in molar volume exhibited by most lanthanides under high pressure is often attributed to changes in the degree of localization of their 4f -electrons. We give evidence, based on electrical resistivity measurements of dilute Y(Gd) and Y(Tb) alloys to 120 GPa, that the volume collapse transitions in Gd and Tb metals have different origins, despite their being neighbors in the periodic table. Remarkably, the change under pressure in the magnetic state of isolated Pr or Tb impurity ions in the nonmagnetic Y host appears to closely mirror corresponding changes in pure Pr or Tb metals. The collapse in Tb appears to be driven by an enhanced negative exchange interaction between 4f and conduction electrons under pressure (Kondo resonance) which, in the case of Y(Tb), dramatically alters the superconducting properties of the Y host, much like previously found for Y(Pr). In Gd our resistivity measurements suggest that a Kondo resonance is not the main driver for its volume collapse. X-ray absorption and emission spectroscopies clearly show that 4f local moments remain largely intact across both volume collapse transitions ruling out 4f band formation (delocalization) and valence transition models as possible drivers. The results highlight the richness of behavior behind the volume collapse transition in lanthanides and demonstrate the stability of the 4f level against band formation to extreme pressure.

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confidence: 80%

“…In analogy to actinides, the localized character of the lanthanide 4f level is expected to change under sufficient pressure. 7 In particular, a sudden pressure-induced drop in the molar volume, commonly termed "volume collapse", has been observed in Ce (16% volume collapse at 0.7 GPa), 8,9 Pr (9.1% at 21 GPa),…”

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confidence: 99%

Different routes to pressure-induced volume collapse transitions in gadolinium and terbium metals

et al. 2013

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“…The theory and characterization of solid-solid isostructural phase transitions has been an area of intense experimental and theoretical research since they were described in 1949 [1]. What sets these transitions apart from others is that while crystalline properties change-sometimes discontinuously-crystallographic structure does not, making these transitions purely electronic in nature.…”

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confidence: 99%

“…Both first order and continuous transitions are known to exist. A well known example of the former is the γ → α transition in fcc Ce [1], while a magneto-volume instability in fcc Fe is an example of the later [2].…”

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confidence: 99%

Topological Catastrophe and Isostructural Phase Transition in Calcium

2010

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We predict a quantum phase transition in fcc Ca under hydrostatic pressure. Using density functional theory, we find at pressures below 80 kbar, the topology of the electron charge density is characterized by nearest neighbor atoms connected through bifurcated bond paths and deep minima in the octahedral holes. At pressures above 80 kbar, the atoms bond through non-nuclear maxima that form in the octahedral holes. This topological change in the charge density softens the C elastic modulus of fcc Ca, while C44 remains unchanged. We propose an order parameter based on applying Morse theory to the charge density, and we show that near the critical point it follows the expected mean-field scaling law with reduced pressure. PACS numbers:The theory and characterization of solid-solid isostructural phase transitions has been an area of intense experimental and theoretical research since they were described in 1949 [1]. What sets these transitions apart from others is that while crystalline properties change-sometimes discontinuously-crystallographic structure does not, making these transitions purely electronic in nature. Both first order and continuous transitions are known to exist. A well known example of the former is the γ → α transition in fcc Ce [1], while a magneto-volume instability in fcc Fe is an example of the later [2].In the case of Fe, the traditional local order parameter, µ, gave conflicting results computationally, with the transition appearing as first [3] or second [2] order. It was not until the transition was interpreted as a topological change of the elctronic charge density, ρ( r), that the underlying nature of the phase change became apparent [4]. While this approach is promising, no general correlations have been drawn between isostructural phase transitions and ρ( r). We use this approach to predict an isostructural phase transition in calcium under hydrostatic pressure. We then apply Morse theory to the charge density and propose an order parameter for the transition. We show that this order parameter scales in the appropriate way with reduced pressure near the quantum critical point.One of the advantages of casting theories of isostructural phase transition in terms of ρ( r) is that it is a quantum observable. Though ρ( r) is often calculated by way of first principles methods (e.g. density functional theory (DFT)), the total charge density can also be measured via X-ray diffraction techniques, and the spin-polarized charge density can be determined using spin-polarized neutron diffraction. As it is also known that all ground state properties depend on the charge density [5], it seems appropriate to seek relationships between the structure * Electronic address: trjones@mines.edu of ρ( r), changes to that structure, and corresponding changes to properties. We note that previous work has proposed that DFT could be used as a general framework for analyzing quantum phase transitions in electronic systems [6].The electron charge density is a 3 dimensional scalar field. Morse theory tells us the ...

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“…It is perhaps best known for its pressure-and temperatureinduced isostructural transition between two phases ( and ), where the face-centered-cubic (fcc) crystal structure is preserved, but the atomic volume changes by $15% at 0.8 GPa and room temperature [1,2]. The physics of this transition has been, and is to this day, intensely debated.…”

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Lattice Dynamics and Superconductivity in Cerium at High Pressure

et al. 2012

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We have measured phonon dispersion relations of the high-pressure phase cerium-oC(4) (alpha phase with the alpha-uranium crystal structure) at 6.5 GPa by using inelastic x-ray scattering. Pronounced phonon anomalies are observed, which are remarkably similar to those of alpha-U. First-principles electronic structure calculations reproduce the anomalies and allow us to identify strong electron-phonon coupling as their origin. At the low-pressure end of its stability range, Ce-oC4 is on the verge of a lattice-dynamical instability and possibly a charge density wave. The superconducting transition temperatures of the fcc, oC4, and mC4 phases of Ce have been calculated, and the superconductivity observed experimentally by Wittig and Probst is attributed to the oC4 phase.Funding Agencies|United Kingdom Engineering and Physical Sciences Research Council||Wenner-Gren Foundation, Sweden||Swedish Foundation for Strategic Research||European Research Council||eDIKT initiative|41

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Concerning the High Pressure Allotropic Modification of Cerium

Cited by 263 publications

References 1 publication

Different routes to pressure-induced volume collapse transitions in gadolinium and terbium metals

Different routes to pressure-induced volume collapse transitions in gadolinium and terbium metals

Topological Catastrophe and Isostructural Phase Transition in Calcium

Lattice Dynamics and Superconductivity in Cerium at High Pressure

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