High-pressure (HP) electrical resistivity measurements of superconducting quasi-skutterudite Y5Rh6Sn18 single crystals were conducted up to 10.7 GPa using a diamond anvil pressure cell. Additionally, HP synchrotron X-ray powder diffraction (XRPD) studies were performed on Y5Rh6Sn18 up to 8 GPa and Sc5Rh6Sn18 up to 11.7 GPa, along with HP Raman spectroscopy. At ambient conditions, the Y5Rh6Sn18 single crystal shows an onset 3.60 K, which increases to a maximum of 3.94 K at 7.89 GPa. Beyond this pressure, further increases lead to a slight decline in Tc. Furthermore, the bad metal nature of the Y5Rh6Sn18 single crystal is suppressed by external pressure, with the residual resistivity ratio (RRR) value increasing from 0.77 to 0.92. The activation energy for electric conduction (Ea) decreases from 2.74 meV at 0.62 GPa to 0.39 meV at 10.65 GPa, indicating enhanced metallic behaviour. Additionally, four Raman vibrational modes are observed, which exhibit a smooth blue shift with increasing pressure up to 9.6 GPa, similar to that of its sister compound Sc5Rh6Sn18. Both Y5Rh6Sn18 and Sc5Rh6Sn18 crystallize in the tetragonal I41/acd space group. With increasing external pressure up to 7 GPa, these compounds exhibit a smooth reduction in unit-cell volume without any structural phase transitions, as described by a second-order Birch-Murnaghan equation of state. Above 7 GPa, Sc5Rh6Sn18 also shows an upturn in both lattice parameters a and c and unit cell volume, while an upturn in only the lattice parameter c (and consequently on unit cell volume) is observed for Y5Rh6Sn18 at 7 GPa. The deviation in the lattice parameter at higher pressure in Y5Rh6Sn18 seems to correlate with the observed decline in Tc with pressure. First-principles calculations under pressure reveal a moderate increase in the density of states (DOS) up to ~ 10 GPa, followed by a slight decrease for higher pressures, a trend which is similar to the observed critical temperature. Furthermore, from theory it is clear that the structure remains stable up to approximately 30 GPa.
Lingannan et al. (Tue,) studied this question.