High-pressure, low-temperature studies of phase transitions in SrRuO3 – Absence of volume collapse

We report powder diffraction data measured on SrRuO3 to pressures of 88 ​GPa ​at ambient temperature. The perovskite structure is found to persist up to the highest pressure measured, but the system undergoes a continuous transition consistent with a 2nd order phase transition to the monoclinic space group P21/n near 25 ​GPa. Fitting the P–V data with the 2nd order Birch-Murnaghan EoS yielded a bulk modulus of K0 ​= ​177.4(10) GPa. Four high-pressure low-temperature experiments have been performed to resolve discrepancies in previous studies. SrRuO3 cooled to 6 ​K ​at near-constant pressures of 10 ​GPa and 40 ​GPa showed no volume collapse during cooling. A compression experiment conducted at 6 ​K up to 65 ​GPa, showed a structural transition to the P21/n space group at 28 ​GPa, and fitting the P–V data with a 3rd order Birch-Murnaghan EoS yielded a bulk modulus of K0 ​= ​154(6) GPa. The experimental data have been compared to DFT calculations. In good agreement with experiments, calculations including ferromagnetic interactions show a structural transition to the P21/n space group at 30–40 ​GPa. Surprisingly, calculations show that the SrRuO3 returns to Pbnm symmetry above 90 ​GPa. The magnetic moment on Ru was predicted to disappear above 70 ​GPa and at the same time the RuO6 octahedra was found to become distorted. The present studies provide a solid ground for further studies of phase relations of SrRuO3 and related perovskites.