Valence of lanthanide oxides

The lanthanide oxides find important applications in the catalysis, lighting, and electronics industries. In particular, the design of advanced devices based upon the integration of lanfhanide oxides with silicon and other semiconductors calls for a defailed undersfanding of the bonding, electronic, and dielectric properties of fhese materials (Scarel et al., 2007). Here, we use the SIC-LSD to address the issue of the lanthanide valence in the dioxides RO2 and sesquioxides R2O3, for R = Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, and Ho. 

FIGURE 16 Energy difference v- ii (in eV per lanthanide ion) between the tetravalent and trivalent lanthanide configurations in dioxides (solid circles) and A-type (hexagonal) sesquioxides (open squares). 

FIGURE 17 Total DOS (solid line) and f-projected DOS (dotted line) for Pr02, with Pr in (A) the pentavalent (f°) configuration, (B) the tetravalent (f ) configuration, and (C) the trivalent (f ) configuration. The SIC localized states are not shown. The energy is in units of eV, with zero marking the Fermi level. 

FIGURE 18 Calculated equilibrium volumes (in A ) of the lanthanide sesquioxides, crystallizing in the hexagonal A-type structure and the cubic C-type structure. The triangles, squares, and circles refer to PAW (Hirosaki et al., 2003), SIC-LSD (present), and experimental results (Eyring, 1978), respectively. 

From experiment, we know that whereas all the lanthanide sesquioxides can be found in nature, the only lanthanide dioxides that occur naturally are Ce02, Pr02, and Tb02. On the other hand, SIC-LSD theory concludes that all the lanthanide sesquioxides prefer the trivalent ground state configuration, whereas the dioxides can be separated into tetravalent light lanthanide dioxides, including 

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