Impact of pressure on the structural, Raman, superconducting, and normal state resistivity properties of Y5Rh6Sn18 quasi-skutterudite single crystal

Abstract

Abstract High-pressure (HP) electrical resistivity measurements of superconducting quasi-skutterudite Y 5 Rh 6 Sn 18 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 Y 5 Rh 6 Sn 18 up to 8 GPa and Sc 5 Rh 6 Sn 18 up to 11.7 GPa, along with HP Raman spectroscopy. At ambient conditions, the Y 5 Rh 6 Sn 18 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 T c . Furthermore, the bad metal nature of the Y 5 Rh 6 Sn 18 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 (E a ) 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 Sc 5 Rh 6 Sn 18 . Both Y 5 Rh 6 Sn 18 and Sc 5 Rh 6 Sn 18 crystallize in the tetragonal I 4 1 / 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, Sc 5 Rh 6 Sn 18 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 Y 5 Rh 6 Sn 18 at 7 GPa. The deviation in the lattice parameter at higher pressure in Y 5 Rh 6 Sn 18 seems to correlate with the observed decline in T c 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.