Theoretical study of the electronic properties ofPrM2B2C(M=Co,Ni,Pt)

Abstract

Full substitution of Ni by the transition metals Co and Pt in $\mathrm{Pr}{M}_{2}{\mathrm{B}}_{2}\mathrm{C}$ $(M=\mathrm{Ni},\mathrm{Co},\mathrm{Pt})$ is analyzed using tight binding within the extended Huckel method. Electronic structure calculation, total and projected density of states (PDOS), Mulliken population, and crystal orbital overlap population analysis were examined in order to elucidate the absent or presence of superconductivity. Band-structure calculation shows small differences in $\mathrm{Pr}∕\mathrm{Ni}$ and $\mathrm{Pr}∕\mathrm{Co}$ compounds. The total and PDOS crossing the Fermi energy $({E}_{F})$ is located in a valley and is dominated by $\ensuremath{-}d$ states, which are principally responsible for the metallic character in both compounds. For $\mathrm{Pr}∕\mathrm{Pt}$ compound, the band structure as well as the total and PDOS are fully different, since two sets of bands, the $\ensuremath{-}f$ and $\ensuremath{-}d$ bands, are highly localized at the ${E}_{F}$, contributing both bands to the electronic conduction. Besides, weak hybridization with important contribution of the C $\ensuremath{-}p$ state is observed in $\mathrm{Pr}∕\mathrm{Pt}$ with respect to the $\mathrm{Pr}∕\mathrm{Ni}$ and $\mathrm{Pr}∕\mathrm{Co}$ compound, where in these last compounds, the C $\ensuremath{-}p$ contribution is null. Furthermore, Mulliken population analysis and average net charge indicated unfilled $\ensuremath{-}d$ orbital with charge transference inside the ${M}_{2}{\mathrm{B}}_{2}$ layer for $\mathrm{Pr}∕\mathrm{Ni}(\mathrm{Co})$. The situation is totally different for $\mathrm{Pr}∕\mathrm{Pt}$ superconductor compounds, since an almost filled $\ensuremath{-}d$ orbital and homogeneous charge distribution were observed. These theoretical evidences suggest that the absence of the superconductivity in $\mathrm{Pr}∕\mathrm{Ni}$ and $\mathrm{Pr}∕\mathrm{Co}$ are connected by the remarkable instabilities between $\ensuremath{-}d$, $\ensuremath{-}p$, and $\ensuremath{-}f$ states, with respect to that observed in the superconductor $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ compounds.