HIGH-TEMPERATURE PHASES OF SRRUO3

The crystal structure of SrRuO3 at high temperatures has been studied using powder neutron diffraction and the Rietveld method. It was deter mined that from 300 K to approximately 820 K the structure of SrRuO3 i s orthorhombic (Pbnm). The material then undergoes a phase transition and becomes tetragonal (I4/mcm) between similar to 820 and 920 K. The high-temperature (>920 K) structure was found to be the standard cubic perovskite (Pm3m). From the neutron-diffraction data and the space gr oup assignments, the orthorhombic to tetragonal phase transition must be first order, while the transition from the tetragonal to cubic phas e is consistent with a second-order phase transition. [S0163-1829(98)0 5425-3].