Synthesis and in situ high pressure Raman spectroscopy study of AlN dendritic crystal

AlN dendritic crystal was synthesized by the direct current arc discharge apparatus. X-ray diffraction (XRD) patterns indicated that the sample is hexagonal AlN and preferentially grown along the a-axis direction. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) images reveal that the product mainly consists of micron AlN dendritic crystal. In situ high pressure Raman spectra of AlN dendritic crystal has been measured in the pressure ranged from ambient pressure to 32.97 GPa at room temperature by using diamond anvil cell. According to the Raman scattering results, the phase transition from the wurtzite to rock salt was found at about 20.73 GPa by the appearance of a new Raman signal. Above 20.73 GPa, a new Raman signal due to disorder-activated Raman scattering in the rock salt phase was observed. In addition, the pressure coefficients, phase transition criterion, and mode Grüneisen parameters of AlN dendritic crystal, which could be different from that of other AlN, are carefully discussed.