Strain‐Driven Selective Stabilization of Metastable TiO₂ Phases

Stabilizing metastable TiO 2 phases in thin films remains a significant challenge. This paper demonstrates a strain‐driven approach for selectively stabilizing the metastable phases of orthorhombic TiO 2 ‐II and rutile using (111)‐oriented face‐centered cubic (FCC) metal substrates via low‐temperature atomic layer deposition. Epitaxial FCC metal substrates, including Ir and Pt, exhibit a strong preferential (111) orientation and promote the formation of TiO 2 ‐II with a preferential (200) orientation through favorable lattice matching. In contrast, TiO 2 grown on (111)‐textured polycrystalline FCC metals crystallizes into rutile with a preferential (110) orientation despite identical growth conditions, which is attributed to strain relaxation arising from the random in‐plane orientations of FCC metals. Compared to the stable anatase phase, TiO 2 ‐II films exhibit higher density (4.45–4.51 g cm −3 ), higher refractive indices, and higher dielectric constants (≈75–77). These findings reveal that in‐plane strain and lattice matching can be strategically utilized to engineer metastable TiO 2 phases, offering a new approach for the phase‐selective growth of functional oxide films at low temperatures.