Formation of preferentially oriented Y3Al5O12 film on a reactive sapphire substrate: Phase and texture transitions from Y2O3

Yttrium aluminum garnet (Y3Al5O12, YAG) thin films were synthesized by reacting sol-gel derived Y2O3 <1 1 1>-oriented films with sapphire substrates. Phase development and inheritance of crystallographic orientation during the formation of YAG was investigated. The major sequence of the phase development from Y2O3 to YAG with increasing temperature was Y2O3 → hexagonal yttrium aluminate (YAlO3, YAH) → YAG, showing that the diffusion of Al3+ into Y2O3 films occurred. The highly {101¯1} -textured YAH phase, which was first synthesized in the present study, would inherit the preferred {1 1 1} plane of self-textured Y2O3 with structural similarity. The YAG phase also showed highly preferred <2 1 1> orientation (Lotgering's factor, F = 0.57) only when the films were prepared on the sapphire (0 0 0 1) substrate. X-ray pole figure and electron backscatter diffraction results suggested an epitaxial growth of {2 1 1}-textured YAG, which was supported by the consideration of lattice matching between the planes of YAG (2 1 1) and sapphire (0 0 0 1).