Influence of the initial crystallinity on the high pressure–high temperature phase transition in boron nitride

Abstract The high pressure–high temperature phase transition behavior of boron nitride powders is investigated. These starting materials differ in their initial crystallinity ranging from highly crystalline to amorphous powders. A convenient way to produce structurally disordered phases is mechanical milling. It is shown that quite short milling times are sufficient for nearly complete amorphization. Under high pressure increasing disorder facilitates the transition to the cubic BN phase. The necessary thermodynamic conditions are considerably lowered compared to highly crystalline starting materials.