Physical properties and structural chemistry of Ce(${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$${)}_5$ alloys

The Ce(${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ga}}_{\mathit{x}}$ ${)}_5$ system has been investigated in the range from x=0 to x∼0.6 including measurements of (a) the lattice parameters at room temperature and down to 4 K on samples quenched from 600 or 800 °C, respectively, (b) the magnetic susceptibility in the temperature range 1.5 <T<800 K and magnetization measurements up to 8 T, (c) the electrical resistivity from 4.2 to 300 K, (d) the specific heat from 1.5 to 60 K and (e) x-ray absorption spectroscopy (XAS) and x-ray absorption near-edge structure (XANES) at 10 and ∼290 K. At 800 °C, a continuous solid solution 0≤x≤0.55 is observed crystallizing with the ${\mathrm{CaCu}}_5$ type. Within this solution range a ${\mathrm{HoNi}}_{2.6}$ ${\mathrm{Ga}}_{2.4}$-type low-temperature modification develops with a small homogeneity range around ${\mathrm{CeNi}}_3$ ${\mathrm{Ga}}_2$ and with a maximum congruent transformation point at T≃770 °C. The Ni/Ga substitution leads to a successive occupation of the 3g sites of P6/mmm symmetry by Ga, whereas the 2c sites are Ga free, but ultimately does not reach full atomic order at a hypothetical ‘‘${\mathrm{CeNi}}_2$ ${\mathrm{Ga}}_3$.’’ Magnetism within the solid solution starts with a nonmagnetic ground state of the cerium atoms in ${\mathrm{CeNi}}_5$ but subsequently changes to an intermediate Ce valence as the Ga content increases.