Where Is the Unmatched Transition Metal in Substoichiometric Diboride Line Compounds?

The atomic structure and local composition of high quality epitaxial substoichiometric titanium
diboride (TiB1.9) thin film, deposited by unbalanced magnetron sputtering, were studied using
analytical high-resolution scanning transmission electron microscopy, density functional theory
and image simulations. The unmatched Ti is pinpointed to planar defects on {1-100} prismatic
planes and attributed to the absence of B between Ti planes that locally relaxes the structure.
This mechanism allows the line compound to accommodate the off-stoichiometry and remain
a line compound between defects. The planar defects are embedded in otherwise stoichiometric
TiB2 and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond
lengths along and across the faults is observed.
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