The Valence States of Ytterbium in Dilute Al-Yb Alloys
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ORIGINAL PAPER
The Valence States of Ytterbium in Dilute Al-Yb Alloys Viktor Bykov 1,2 & Sergey Uporov 1,2 Received: 11 September 2020 / Accepted: 1 October 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Magnetic susceptibility of a series of hypoeutectic Al-Yb alloys has been investigated in a wide temperature range from 300 to 1650 K. A step-like drastic change in the magnetic susceptibility at melting point has been discovered for the first time. The anomaly is interpreted as a temperature-induced valence transition. The substitution aluminum by gallium shifts the valence transition to room temperature. The valence states of ytterbium in both systems are discussed for solid and liquid phases. Keywords Mixed-valence state . Magnetic susceptibility . Rare earth . Melts
1 Introduction Valence fluctuation occurring in some rare-earth systems is one of the intriguing phenomena of condensed matter physics. This field is under intensive consideration by many research groups since 1912 [1]. A temperature-and-pressure-induced electronic phase transition was first discovered in cerium metal [2]. This effect is caused by an isomorphic first-order phase transition from γ-Ce to α-Ce. A valence change (VC) in the rare-earth compounds is mostly observed under high pressures and low temperatures [1–4]. For example, samarium compounds as such SmS, SmSe, and SmTe clearly demonstrate the VC due to isostructural first-order semiconductor-metal transition under pressure 10–100 kbar [3]. Up-to-date, the intermediate valence materials, due to their anomalous physical properties, remain a subject of numerous theoretical and experimental researches. A multiplicity of rare-earth substances exhibiting VC behavior under various conditions has already been found. Among them are ytterbium metal and some of its compounds. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10948-020-05713-w) contains supplementary material, which is available to authorized users. * Sergey Uporov [email protected] 1
Institute of Metallurgy, Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia 620016
2
Ural Federal University named after First President of Russia B.N. Yeltsin, Ekaterinburg, Russia 620000
It well known that ytterbium can demonstrate divalent (Yb2+) and trivalent (Yb3+) states. The first state is characterized by closed 4f shell and hence, the Yb atom is non-magnetic, whereas in the second case, it has one vacation in the 4f shell, leading to a magnetic moment of 4.54 μB. A mixedvalence state is frequently observed for Yb compounds. Its valence configuration was found to significantly depend on temperature, pressure, or magnetic field. Owing to the valence fluctuation, the Yb-containing compounds and alloys often exhibit anomalous physical properties. The mixed-valence state in Yb occurs because the 4f band is located closely to the Fermi level, and therefore, weak localized 4f electrons can be involved into chemical interaction. Similar behavior has previ
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