[en] 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 230 μg, and typically have transition temperatures between 37 and 39 K 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 deg. C at high hydrostatic pressure in the presence of Mg vapor under high pressure. Small variations of T_c are caused by doping with metal elements from the precursor or annealing of defects during the crystal growth process