${\mathrm{Eu}}_2$${\mathrm{Ni}}_3$${\mathrm{Si}}_5$: A new valence-fluctuation system

In our search for new valence-fluctuating systems, we have synthesized for the first time the compound ${\mathrm{Eu}}_2$ ${\mathrm{Ni}}_3$ ${\mathrm{Si}}_5$. The powder x-ray-diffraction pattern shows that the compound forms in the orthorhombic ${\mathrm{U}}_2$ ${\mathrm{Co}}_3$ ${\mathrm{Si}}_5$-type structure. The value of the isomer shift of the ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ Mössbauer resonance (-2.8 mm/sec at 300 K) and its strong temperature dependence (-1.1 mm/sec at 4.8 K) clearly establish that the Eu ion in this system is in a valence-fluctuating state. The average valence varies from 2.6 at 300 K to 2.8 at 4.8 K. The valence-fluctuating nature is further confirmed by magnetic-susceptibility studies.