Valence lanthanide sesquioxides

Semiempirical calculations of free energies and enthalpies of hydration derived from an electrostatic model of ions with a noble gas structure have been applied to the ter-valent actinide ions. A primary hydration number for the actinides was determined by correlating the experimental enthalpy data for plutonium(iii) with the model. The thermodynamic data for actinide metals and their oxides from thorium to curium has been assessed. The thermodynamic data for the substoicheiometric dioxides at high temperatures has been used to consider the relative stabilities of valence states lower than four and subsequently examine the stability requirements for the sesquioxides and monoxides. Sequential thermodynamic trends in the gaseous metals, monoxides, and dioxides were examined and compared with those of the lanthanides. A study of the rates of actinide oxidation-reduction reactions showed that, contrary to previous reports, the Marcus equation ... 

In this chapter we have shown that the thermochemistry of the rare-earth oxides is well established for the majority of the stoichiometric compounds. The thermodynamic properties follow clear trends that can be understood in terms of valence states and electronic configurations of the lanthanide ions and metals. For the sesquioxides, the principal group of rare earth compounds, the data are reliable up to 2000 K, an interval in which the A, B and C phases are stable. However, for the high-temperatures, where the H and X phases are stable, no experimental data exist. 

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. 

Rare earth elements are very reactive with ambient oxygen, and the oxides are the most stable form of the element. The lanthanide elements generally acquire a -1-3 valence state and acquire sesquioxide combinations with oxygen to form M2O3 with some variances. For several of the lanthanide elements, the +2 and -1-4 oxidation states are stable. Cerium... 

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