  Dark blue single crystals of Al$_{1.75}^{3+}$ Ti$_{1.0}^{4+}$
Ti$_{0.25}^{3+}$O$_5$ were grown with a novel synthesis method based on the
reaction of a Ti3+/Ti4+ containing langbeinite melt and Al$_2$O$_3$. The
obtained needles crystallize in the pseudobrookite structure and undergo two
reversible phase transitions from orthorhombic Cmcm to C2/m first and
subsequently to C2 symmetry. Like the known aluminum titanate pseudobrookites,
anistropic thermal expansion is observed. The temperature evolution of the
crystal structure reveals some insights into the mechanism leading to the
decomposition of the Al$_{1.75}$Ti$_{1.25}$O$_5$ above 725$^\circ$C. The
magnetic and electrical properties are discussed and compared to other reported
aluminum titanate pseudobrookites.
