Introduction: It is well known that Lanthanide ions have a common stable valence, 3+. Due to its electron configuration (Xe)4f146s2, a divalent Ytterbium (Yb) ion might be stable. Although EuO with the electron configuration (Xe)4f7 6s2 has been known to be stable and is commercially available, there has been less reports for synthesizing the metastable Ytterbium oxide; YbO. It was suggested that YbO could exist as a metastable phase because the standard Gibbs energy change (⊿G0) was very close to 0 by the theorerical calculation in the reaction (1) as shown in Fig. 1 .
Ln + Ln2O3 → 3 Ln2+O2- (1) Leger et al.  reported the formation of YbO by the reaction Yb + Yb2O3 under very high pressure at 50 kbar, and Fishel er al.  reported its formation by the reaction of oxygen with ytterbium in liquid ammonia. But their methods such as very high pressure and ultralow temperature seems to be unrealistic when considering the industrial production. So far, there has been no report on the synthesis of YbO under the normal pressure.
In this work, the solid-state synthesis of YbO has been investigated by the oxidation of Yb metal under the normal pressure using two methods; 1) heat treatment of Yb metal under Ar gas atmosphere with metal carbonate as an oxygen source, and 2) heat treatment of Yb metal under continuous gas flow using various gas atmospheres, Ar-O2, Ar-CO and Ar-CO2 in the tube furnace changing the ratio of mixed gas, temperature and retention time. A mechanism for the formation of YbO under various gas atmospheres was discussed using the X-ray diffraction (XRD) and Scanning Electron Microscope (SEM).
Authors: Aoi Goto, Yoshio Ohta, and Mikito Kitayama
Keywords: Lanthanides, Solid-State Synthesis, Ytterbium (II) Oxide