For the first time, we experimentally detected the formation of 6-fold symmetry patterned microcrystals of AlN (aluminum nitride), such as simple prisms, stellar and sectored plates, and stellar and fernlike stellar dendrites. These crystals were formed during combustion of a solid mixture of Al + kAlF3 (k = 0.05-0.1 mol) under a nitrogen atmosphere (PN2 = 2.5 MPa). The combustion temperature recorded with a thermocouple was in the 1700-1900 °C range. We examined the physical mechanisms governing the formation of AlN crystals, and we treated this problem as a case study of the dynamics of crystal growth from the liquid phase. Particular attention was given to the basic theoretical understanding of the subject, utilizing first-principles density functional theory calculations. The Wulff construction method was applied to identify equilibrium structures of nano- and microscale AlN crystals. Energy minimization arguments were used to show that certain crystal planes of AlN are more probable than others, giving the crystal 6-fold symmetry. The integrated experiments and computations form the basis for our proposal of the underlying mechanisms for nucleation and growth of the AlN crystals.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics