A 1ST-PRINCIPLES STUDY OF COMPRESSION TWINS IN HCP ZIRCONIUM

Using fully self-consistent ab-initio techniques, we have determined v alues for {1122BAR} and {1011BAR} compression twin-boundary energies i n h.c.p. zirconisum. Experimentally, c-axis compression produces {1122 BAR} twins at temperatures below about 800 K; it has been suggested th at this is due to the low energy of this type of twin. We find that th e {1011BAR} boundary has a much lower energy than the {1122BAR} bounda ry, by a actor of four. Thus the ease of {1122BAR} formation at low te mperatures must be due to the other causes, such as a low barrier to t win nucleation.