Based on the designed structures, the calculations of geometry
optimization are performed in first principle theory VASP code. After
full geometry optimization, the structures of
Ti3AlB2 and two designed
Ti2ZrAlB2 keep their symmetry as shown
in Figure 1. And the calculated equilibrium structural data and the bond
lengths are listed in Table 1. For two
Ti2ZrAlB2 structures, it is easy to
understand that the bond lengths of Zr-B and Ti-B are different. But for
Ti3AlB2, the bond lengths of Ti(1)-B and
Ti(2)-B are different, and the former is slightly longer than the
latter. Similar phenomena have been found in
Ti3AlC2 and
Ti3SiC2 [33-34].
Ti3AlB2 can be regarded as formed by
introducing Al element into Ti-B compound. The introduction of this
element changes the bonding environment of Ti atom, and it leads to the
increase of partial bond length and the decrease of partial bond length
of Ti-B bond in the structure. Thus, two types of Ti-B bonds with
different bond lengths appeared in
Ti3AlB2 structure.