The structures of the intermediate phases ZrsSc2013 and Zr3Sc4Ol2 in the system ZrO2-Sc203 have been determined from intensity data obtained with a H/~gg-Guinier focusing X-ray powder camera and Cu Ket radiation. The space group in both cases is R3, and the hexagonal unit-cell dimensions are respectively a=9-53(2), c=17.44(2),~ and a=9.37(8), c=8.71(0)A. Both these structures are derived from the fluorite-type parent MO2 by ordered omission of oxygen atoms; the observed rhombohedral distortion is the result of lattice relaxation. It is possible to recognize structural sub-units from which these and other fluorite-related structures can be built up. Such sub-units are likely to play an important role in any adequate description of grossly non-stoichiometric phases.

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