Nitrides of boron & silicon are  used to make crucibles because they are stable when this is high
[DOC] [TLE] Crucibles - Dr. Eberl MBE-Komponenten GmbH [PAR] Pyrolytic boron nitride (PBN) crucibles have become the accepted crucible 
material for use in MBE growth of semiconductor materials because of the 
material's high purity, chemical inertness, thermal stability, low outgassing, ... 
tantalum (Ta), pyrolytic graphite (PG), silicon dioxide (quartz), aluminum oxide (Al
2O3), beryllium... [DOC] [TLE] Boron Nitride - Stanford Advanced Materials [PAR] The hexagonal BN is similar with graphite while cubic boron nitride behaves like 
diamonds.