  Sub-oxides with the anti-perovskite structure constitute a large part of the
interstitial stabilized compounds with novel chemical and physical properties,
especially in the systems containing rare earth elements and/or early
transition metal elements. A new sub-oxide compound,
(Ce$_{0.85}$Ti$_{0.15}$)Ge$_3$O$_{0.5}$, is synthesized by flux growth. The
compound crystallizes in a cubic structure which can be considered as an
ordered vacancy variant of anti-perovskite-structure or an ordered interstitial
variant of the Cu$_3$Au type, with a space group of Fm-3m (225). The structure
is refined from X-ray single crystal methods. The compound may be considered as
a compound stabilized by chemical pressure generated by the substitution and
the interstitials atoms. The stability of the compounds in RTr$_3$ systems (R =
rare earth elements except Pm and Sc, Tr = tetrel elements such as Si, Ge, Sn,
Pb) seem to be highly correlated to the ratio of the rare earth elements' radii
to the main group elements' atomic radii. The magnetic property of the compound
confirms the 4$^+$ valence of the Ce atoms. The resistivity measurement of the
compound shows that it is metallic.
