Electronic Phase Transitions in F-electron Metals at High Pressures: Synchrotron X-ray Spectroscopic Studies on GD to 10
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1104-NN01-02
ELECTRONIC PHASE TRANSITIONS IN F-ELECTRON METALS AT HIGH PRESSURES: SYNCHROTRON X-RAY SPECTROSCOPIC STUDIES ON GD TO 100 GPa Choong-Shik Yoo1, Brian Maddox2, and Valentin Iota2 1 Department of Chemistry and Institute for Shock Physics, Washington State University, Pullman, WA, 99164 2 Lawrence Livermore National Laboratory, Livermore, CA, 94551 ABSTRACT Unusual phase transitions driven by electron correlation effects occur in many felectron metals (lanthanides and actinides alike) from localized phases to itinerant phases at high pressures. The dramatic changes in atomic volumes and crystal structures associated with some of these transitions signify equally important changes in the underlying electronic structure of these correlated f-electron metals. Yet, the relationships among the crystal structure, electronic correlation and electronic structure in f-electron metals have not been well understood. In this study, utilizing recent advances in thirdgeneration synchrotron x-ray spectroscopies and high-pressure diamond-anvil cell technologies, we describe the pressure-induced spectral changes across the volume collapse transition in Gd at 60 GPa and well above. The spectral results suggest that the felectrons of high-pressure Gd phases are highly correlated even at 100 GPa – consistent with the Kondo volume collapse model and the recent experimental evidence of strong electron correlation of α-Ce. INTRODUCTION The f-electron metals, actinides and lanthanides alike, exhibit a profound change in character, both for individual metals as a function of compression, or across the series as a whole at ambient pressure, as illustrated in Fig. 1 [1]. The early part, from Th-Pu, shows a parabolic behavior of the equilibrium molar volume reminiscent of the d-transition metals, whereas the later part shows a more constant behavior of the specific volume as a function of atomic number. The similarity between the light actinides and the d-transition metals in this regard is governed by the fact that the light actinides and the d-transition metals both have delocalized electrons, f and d respectively. For the heavier actinides
Figure 1. Specific volumes of f- and delectron transition metals plotted as a function of their band actinides occupancy. Divalent Eu and Yb are the exceptions to the systematic behavior of other trivalent rareearth metals.
from americium and on, however, the 5f electrons are localized similar to the lanthanide series and their properties become quite different from that of the earlier actinides. Plutonium, at the central position of the two trends, exhibits a dramatic effect with a subtle change in lattice induced by pressure, temperature and impurities [2]. For example, Pu at ambient conditions crystallizes into low symmetry monoclinic α-Pu with 16 atoms per unit cell suggesting itinerant electrons participating in bonding, whereas at slightly elevated temperatures it undergoes a series of phase transitions to high symmetry fcc δPu with localized 5f electrons. Because of this fundamental d
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