Single-crystal neutron diffraction investigations on the phase transitions in CeO1.800 and CeO1.765

Information on the controversial phase diagram of CeOy (1.65 < y less than or equal to 2.0) was obtained by making single-crystal neutron scattering measurements on CeO1.800 and CeO1.765 up to 1064 K. The observed phase transitions at 755 K, 823 K, 866 K, and 898 K when the temperature is raised (or 738 K, 773 K, 845 K, and 898 K when T is lowered) for CeO1.800 as well as the observed phase transition at 911 K (907 K) for CeO1.765 qualitatively confirm the phase diagram proposed previously by Ricken et al. The crystal structures of all the observed phases apparently are of rhombohedral symmetry (space group R (3) over bar). (C) 2000 Academic Press.