A unibody, multi-piece crucible for use in for use in elemental purification, compounding, and growth of semi-conductor crystals, e.g., in the process of molecular beam epitaxy (MBE) for melting silicon and the like at high temperature. The crucible has an outer coating layer that fixedly joins the multi pieces making up the crucible. The invention also provides a method for making a unibody containing structure comprising pyrolytic boron nitride having a negative draft, which method obviates the need of complicated overhang structure of graphite mandrels or the removal of the graphite mandrels by burning at high temperatures.