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

Abstract

We theoretically examine four hypothetical ternary lanthanide hydrides, CsLn^IIH₃ and Cs₂Ln^IIH₄, 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^IIH₂); ternaries would form only under elevated pressure (>7–22 GPa). We predict that significant perturbation of the electronic and magnetic properties of CsYb^IIH₃ and Cs₂Yb^IIH₄ will take place via a progressive exchange of f¹⁴ Yb^II for f¹³ Tm^II, while promoting magnetic ordering and valence fluctuations. Analysis of the phonon dispersion for these hydrides suggests that metallic forms of doped CsLn^IIH₃ and Cs₂Ln^IIH₄ would exhibit substantially high Debye temperatures of ∼1800 K. This is likely to prompt moderate-T_C superconductivity in these as yet unknown materials.