High-temperature phases of ${\mathrm{SrRuO}}_3$

The crystal structure of ${\mathrm{SrRuO}}_3$ at high temperatures has been studied using powder neutron diffraction and the Rietveld method. It was determined that from 300 K to approximately 820 K the structure of ${\mathrm{SrRuO}}_3$ is orthorhombic $\mathrm{}\left(\mathrm{Pbnm}\right).$ The material then undergoes a phase transition and becomes tetragonal $\mathrm{}(I4/mcm)\mathrm{}$ between ∼820 and 920 K. The high-temperature (>920 K) structure was found to be the standard cubic perovskite $\mathrm{}\left(\mathrm{Pm}3m\right).$ From the neutron-diffraction data and the space group assignments, the orthorhombic to tetragonal phase transition must be first order, while the transition from the tetragonal to cubic phase is consistent with a second-order phase transition.