A first-principles study of compression twins in h.c.p. zirconium

Using fully self-consistent ab-initio techniques, we have determined values for{1122} and {1011} compression twin-boundary energies in h.c.p. zirconium. Experimentally, c-axis compression produces {1122} twins at temperatures below about 800 K; it has been suggested that this is due to the low energy of this type of twin. We find that the {1011} boundary has a much lower energy than the {1122} boundary, by a factor of four. Thus the ease of {1122} formation at low temperatures must be due to the other causes, such as a low barrier to twin nucleation.