Pressure-induced modification of the electron structure of metallic thorium

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ONIC PROPERTIES OF SOLID

PressureInduced Modification of the Electron Structure of Metallic Thorium A. V. Lukoyanova,b,*, M. O. Zaminevb, and V. I. Anisimova,b a

Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620990 Russia b Ural Federal University, Yekaterinburg, 620002 Russia *email: [email protected] Received July 11, 2013

Abstract—The electronic structure of thorium (Th) in low and hightemperature cubic phases under nor mal conditions and pressure has been studied using the LDA + U + SO method. Since a correct description of the physical properties of Th and other metals of the actinide series requires taking into account both the spin–orbit coupling and Coulomb interactions, the parameters of these interactions have been additionally calculated. It is established that applied pressure leads to broadening of the 5f electron states in metallic Th and causes a significant increase in their population. DOI: 10.1134/S1063776114010105

1. INTRODUCTION Thorium (Th) is a metal of the actinide series, which has been actively studied in recent years because of the possibility of using this metal as a fuel in new generation nuclear reactors [1]. Longlived actinides that form in the thorium cycle are present in lower amounts and are characterized by much shorter decay periods than products that form in the uranium and plutonium cycles. From the standpoint of ecological protection, this is an important factor in developing safe nuclear power engineering. Therefore, investiga tion of the properties of thorium under extremal con ditions (elevated temperatures and pressures, etc.) is an interesting and topical task [2]. The physical properties of metallic thorium have been studied by various experimental methods. Under normal conditions, thorium crystallizes in a facecen tered cubic (fcc) lattice of the lowtemperature alpha phase (αTh) [3]. At temperatures above 1400°C, a bodycentered beta phase (βTh) has been observed [4]. A phase transition from the fcc to a bodycentered tetragonal (bct) lattice takes place at pressures above 100 GPa. However, measurements of the pressure dependence of lattice parameters showed the exist ence of a rather small tetragonal component [5]. Fea tures of the electronic structure of Th have been stud ied experimentally by Xray photoemission and bremsstrahlung isochromat spectroscopy [6]. Earlier, the electronic structure of thorium was studied by band structure calculations with significant restrictions. Initially, the calculations were performed in a simple local density approximation (LDA) and Th was assumed to be a tetravalent dtransition metal with completely occupied 5f states, so that the 5f bands were artificially shifted to higher energies [7]. How

ever, subsequent calculations showed that allowance for 5f electrons provided better agreement with the experimentally measured [7–9] Fermi surface [10, 11]. Linearized muffintin orbital (LMTO) calcula tions [12] led to the conclusion that Th under high pressure is a 5fband met

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