The intermetallic compound ${\mathrm{YbCu}}_2{\mathrm{Si}}_2$ is a well-known nonmagnetic (NM) Yb intermediate-valent compound with a Yb valence of 2.9 at ambient pressure and 300 K. In the present work we have investigated the effect of high pressure on the ground state properties of ${\mathrm{YbCu}}_2{\mathrm{Si}}_2$ on both microscopic and macroscopic levels by using the ${}^{170}\mathrm{Yb}$ Mössbauer effect, electrical resistance, and x-ray diffraction techniques, respectively. High-pressure x-ray diffraction data indicate that the lattice structure of ${\mathrm{YbCu}}_2{\mathrm{Si}}_2$ is stable up to 22.2 GPa. The value of the bulk modulus $[B_0=168\mathrm{}(10\left)\mathrm{}{\mathrm{GPa}}^{-1}\right]$ is found to be close to the value expected for trivalent $R{\mathrm{Cu}}_2{\mathrm{Si}}_2$ compounds. The pressure dependence of the electrical resistance reveals evidence for a pressure-induced magnetic order for $p>~8\hspace{0.5em}\mathrm{GPa}$. From our Mössbauer data, we conclude a crossover from the NM to a magnetically ordered state of localized Yb moments for $p>~8\hspace{0.5em}\mathrm{GPa}$ and below 2 K. The pressure-induced change of the electric quadrupole splitting indicates that this transition is accompanied by a valence change towards the ${\mathrm{Yb}}^{3+}$ state.

• Received 7 December 1998

DOI:https://doi.org/10.1103/PhysRevB.60.3324