Chemical bonding in theUFe1−xNixAl alloys

Chemical bonding in ${\mathrm{UFe}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ni}}_{\mathit{x}}$Al is interpreted within the framework of nonempirical calculations of charge-density distribution, performed by means of the modified statistical method. Maps of constant density in the principal planes of the crystal structure are presented. It is shown that an electron-density (ED) distribution exhibits a pronounced charge transfer from the [Al-Fe(Ni)] plane towards the [U-Fe(Ni)] plane as the Ni concentration in the alloy changes up to x≊0.3. As a result of such a transfer, the ED distribution in the latter plane becomes largely nonuniform. Chemical bonding within the [Al-Fe(Ni)] group of ions shows mostly a covalent character. Thus, such regions determine, to a large extent, the electric-field gradient at the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nuclei. Results of theoretical investigations of chemical bonding peculiarities in the ${\mathrm{UFe}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ni}}_{\mathit{x}}$Al alloys are compared with Mössbauer-effect data. On this basis we have attempted to explain the anomalous behavior of the lattice parameters in the solid solutions ${\mathrm{UFe}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ni}}_{\mathit{x}}$Al.