Hole Polaronic Confinement in (111) Yttria-Stabilised Zirconia

: Yttria-stabilized zirconia (YSZ) is the benchmark oxygen-ion conductor and is widely regarded as electronically inert under oxidizing conditions. Yet its electrical behavior at the nanoscale remains unsettled. While bulk YSZ exhibits predominantly ionic transport, electronic contributions have only been reported under highly defective, porous, or strong-field conditions. Here, we demonstrate that ultrathin epitaxial YSZ films (<20 nm) exhibit measurable p-type mixed conduction at room temperature arising intrinsically from crystallographically ordered defect-dopant associations. Combined electrical measurements and first-principles modeling show that Y3 +-vacancy complexes stabilize hole polarons confined along specific lattice directions. In (111)-oriented films, interfacial defect ordering produces a high density of confined polarons, enabling directional charge transport and enhanced electro-chemo-mechanical coupling beyond classical electrostriction. These results show that electronic functionality in YSZ can emerge solely from nanoscale defect ordering, redefining its transport behavior beyond the classical purely ionic paradigm and revealing unexpected electromechanical functionality in a canonical ionic oxide.