Why are titanium oxides lumped in with magnetite for the purposes of analyzing water bubble nucleation?
In iron oxides, titanium commonly substitutes for iron in the crystal structure. Two solid solution series are important: the ulvöspinel-magnetite and ilmenite-hematite series.

The composition of a solution changes continuously, without any change in crystal habit. Your reference indicates its the size of crystals than matter for being efficient nucleation sites. Composition is not expected to be important.