  Millimeter-sized single crystals of LaFeAsO, LaFeAsO1-xFx, and LaFe1-xCoxAsO
were grown in NaAs flux at ambient pressure. The detailed growth procedure and
crystal characterizations are reported. The as-grown crystals have typical
dimensions of 3 * 4 * 0.05-0.3 mm3 with the crystallographic c-axis
perpendicular to the plane of the plate-like single crystals. Some crystals
manifest linear dimensions as large as 4-5 mm. X-ray and neutron single crystal
scattering confirmed that LaFeAsO crystals exhibit a structural phase
transition at Ts ~ 154 K and a magnetic phase transition at TSDW ~ 140 K. The
transition temperatures agree with those determined by anisotropic
magnetization, in-plane electrical resistivity and specific heat measurements
and are consistent with previous reports on polycrystalline samples. Co and F
were successfully introduced into the lattice leading to superconducting
LaFe1-xCoxAsO and LaFeAsO1-xFx single crystals, respectively. This growth
protocol has been successfully employed to grow single crystals of NdFeAsO.
Thus it is expected to be broadly applicable to grow other RMAsO (R = rare
earth, M = transition metal) compounds. These large crystals will facilitate
the efforts of unraveling the underlying physics of iron pniticide
superconductors.
