Nanoparticles with a rhombohedral boron nitride (r-BN) structure were synthesized by a chemical vapor deposition method from BCl3-NH3-H-2 gas system at a temperature of 1600 degreesC and a total gas pressure of 3-5 Torr on the graphite substrates. The r-BN nanoparticles with the size of 50-1000 nm showed {101}, {113} and {001} twin structures. Cubic BN was also produced from r-BN under high pressure and high temperature, and {111} twin structure was observed. Electron diffraction patterns calculated based on the atomic structure models of these twin structures agreed well with the observations. (C) 2002 Elsevier Science B.V. All rights reserved.