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.

Graphical abstractA 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 full-size imageDownload as PowerPoint slide