  Higher OH concentration is identified in tetragonal barium titanate
(BaTiO$_3$) nanorods synthesized by a hydrothermal method with 10 vol% ethylene
glycol solvent [Inada, M. $et$ $al$. $Ceram.$ $Int.$ $2015$, $41$, 5581-5587].
This is apparently inconsistent with the known fact that higher OH
concentration in the conventional hydrothermal synthesis makes pseudo-cubic
BaTiO$_3$ nanocrystals more stable than the tetragonal one. To understand where
and how the introduced OH anions are located and behave in the nanocrystals, we
applied $ab$ $initio$ analysis to several possible microscopic geometries of OH
locations, confirming the relative stability of the tetragonal distortion over
the pseudo-cubic one due to the preference of trans-type configurations of OH
anions. We also performed FTIR and XRD analysis, all being in consistent with
the microscopic picture established by the $ab$ $initio$ geometrical
optimizations.
