Preferred orientation of TiB₂ plates prepared by CVD of the TiCl₄ + B₂H₆ system

Titanium diboride (TiB₂) plates (about 1 mm maximum thickness) were prepared by chemical vapour deposition (CVD) using a TiCl₄, B₂H₆ and H₂ system at deposition temperatures, T_dep of 1323-1773 K. The B/Ti atomic ratio in the deposits was 2, and the composition is strictly stoichiometric. Chlorine was not detected. The measured lattice parameters were a=0.3029 nm and c=0.3229 nm. Density is in close agreement with the theoretical value (4.50 g cm^-3). Preferred orientation of the CVD TiB₂ plates varies mainly with total gas pressures, P_tot. At P_tot=4 kPa the (1 0 0) plane and at P_tot=40 kPa the (1 1 0) plane is preferably oriented parallel to the substrates. The effect of P_tot on the preferred orientation is discussed thermodynamically, and explained by supersaturation in the gas phase.