  We have studied the phase diagram of La$_{1-x}$Ca$_{x}$MnO$_{3}$ for $0.5\leq
x\leq 0.9$ using neutron powder diffraction and magnetization measurements. At
300 K all samples are paramagnetic and single phase with crystallographic
symmetry $Pnma$. As the temperature is reduced a structural transition is
observed which is to a charge-ordered state only for certain x. On further
cooling the material passes to an antiferromagnetic ground state with Neel
temperature $T_N$ that depends on x. For $0.8\leq x\leq 0.9$ the structural
transformation occurs at the same temperature as the magnetic transition.
Overall, the neutron diffraction patterns were explained by considering four
phase boundaries for which La$_{1-x}$Ca$_x$MnO$_3$ forms a distinct phase: the
CE phase at $x=0.5-0.55$, the charge-ordered phase at x=2/3, the monoclinic and
C-type magnetic structure at $x=0.80-0.85$ and the G-type magnetic structure at
x=1. Between these phase boundaries the magnetic reflections suggest the
existence of mixed compounds containing both phases of the adjacent phase
boundaries in a ratio determined by the lever rule.
