  The conditions whereby epitaxy is achieved are commonly believed to be mostly
governed by misfit strain. We report on a systematic investigation of growth
and interface structure of single crystalline tungsten thin films on two
different metal oxide substrates, Al$_{2}$O$_{3}$ ($11\bar{2}0$) and MgO
($001$). We demonstrate that despite a significant mismatch, enhanced crystal
quality is observed for tungsten grown on the sapphire substrates. This is
promoted by stronger adhesion and chemical bonding with sapphire compared to
magnesium oxide, along with the restructuring of the tungsten layers close to
the interface. The latter is supported by ab initio calculations using density
functional theory. Finally, we demonstrate the growth of magnetic
heterostructures consisting of high-quality tungsten layers in combination with
ferromagnetic CoFe layers, which are relevant for spintronic applications.
