Possibly Mixed Valency of Uranium in U Ni 5 − x Cu x

This paper reports the lattice constant at room temperature and the susceptibility, specific heat, electrical resistivity, and absolute Seebeck coefficient of compounds $\mathrm{U}{\mathrm{Ni}}_{5\ensuremath{-}x}{\mathrm{Cu}}_{x}$ ($0\ensuremath{\le}x\ensuremath{\le}5$) as a function of temperature. It is suggested that the drastic change in the properties of these compounds when $x$, increasing from 0, comes into the range of 4 to 5 is caused by a change of the uranium ions from a ${\mathrm{U}}^{4+}$ to a mixed ${\mathrm{U}}^{4+}$-${\mathrm{U}}^{3+}$ state.