Hydrothermal hot-pressing induced phase transition in hexagonal boron nitride

The phase transition of hBN nanocrystals induced by hydrothermal hot-pressing process has been investigated by XRD, FTIR, TEM and HRTEM. It was found that a phase transition of hBN → tBN → aBN occurred with increasing hot-pressing temperature, i.e., hBN transformed into tBN at above 270 °C, and followed by another transformation from tBN to aBN at 310 °C. In addition, FTIR spectra and HRTEM images indicate that a small amount of cBN formed directly from the amorphous BN matrix at 75 MPa and 310 °C. This phenomenon is similar to what happened in conventional high temperature and high pressure method, which is believed to promote the phase transition from hBN to cBN.

A transformation of hBN → tBN → aBN may have taken place with the increasing of hot-pressing temperature: hBN transformed into tBN at above 270 °C (d), and followed by another transformation from tBN to aBN at 310 °C (f). Figure optionsDownload as PowerPoint slide