  Single crystals of MgB2 have been grown at high pressure via the peritectic
decomposition of MgNB9. The crystals are of a size up to 1.5x0.9x0.2 mm3 with a
weight up to 0.23 mg, and typically have transition temperatures between 37 and
39 with a width of 0.3-0.5 K. Investigations of the P-T phase diagram prove
that the MgB2 phase is stable at least up to 2190 C at high hydrostatic
pressure in the presence of Mg vapor under high pressure. Small variations of
Tc are caused by doping with metal elements from the precursor or annealing of
defects during the crystal growth process.
