Prediction of thermodynamic stability and electronic structure of novel ternary lanthanide hydrides

We theoretically examine four hypothetical ternary lanthanide hydrides, CsLn(II)H(3) and Cs(2)Ln(II)H(4), where Ln(II) = Yb, Tm. We optimize their crystal unit cells in the BaTiO3 and K2NiF4 structures, respectively, and compute their electronic band structures. Our calculations indicate that the novel hydrides should be unstable with respect to decomposition into binaries (CsH and Ln(II)H(2)); ternaries would form only under elevated pressure (> 7-22 GPa). We predict that significant perturbation of the electronic and magnetic properties of (CsYbH3)-H-II and (Cs2YbH4)-H-II will take place via a progressive exchange of f(14) Yb-II for f(13) Tm-II, while promoting magnetic ordering and valence fluctuations. Analysis of the phonon dispersion for these hydrides suggests that metallic forms of doped CsLn(II)H(3) and Cs(2)Ln(II)H(4) would exhibit substantially high Debye temperatures of similar to 1800 K. This is likely to prompt moderate-T-C superconductivity in these as yet unknown materials.